Kinkazzo Burning
~ reflections & disquisitions
It takes both sunshine and rain to make a rainbow...

Life, the Universe and... What?


Young Planet


The Origin of the Universe, Earth, and Life

The term "evolution" usually refers to the biological evolution of living things. But the processes by which planets, stars, galaxies, and the universe form and change over time are also types of "evolution." In all of these cases there is change over time, although the processes involved are quite different.

In the late 1920s the American astronomer Edwin Hubble made a very interesting and important discovery. Hubble made observations that he interpreted as showing that distant stars and galaxies are receding from Earth in every direction. Moreover, the velocities of recession increase in proportion with distance, a discovery that has been confirmed by numerous and repeated measurements since Hubble's time. The implication of these findings is that the universe is expanding.

Hubble's hypothesis of an expanding universe leads to certain deductions. One is that the universe was more condensed at a previous time. From this deduction came the suggestion that all the currently observed matter and energy in the universe were initially condensed in a very small and infinitely hot mass. A huge explosion, known as the Big Bang, then sent matter and energy expanding in all directions.

This Big Bang hypothesis led to more testable deductions. One such deduction was that the temperature in deep space today should be several degrees above absolute zero. Observations showed this deduction to be correct. In fact, the Cosmic Microwave Background Explorer (COBE) satellite launched in 1991 confirmed that the background radiation field has exactly the spectrum predicted by a Big Bang origin for the universe.

As the universe expanded, according to current scientific understanding, matter collected into clouds that began to condense and rotate, forming the forerunners of galaxies. Within galaxies, including our own Milky Way galaxy, changes in pressure caused gas and dust to form distinct clouds. In some of these clouds, where there was sufficient mass and the right forces, gravitational attraction caused the cloud to collapse. If the mass of material in the cloud was sufficiently compressed, nuclear reactions began and a star was born.

Some proportion of stars, including our sun, formed in the middle of a flattened spinning disk of material. In the case of our sun, the gas and dust within this disk collided and aggregated into small grains, and the grains formed into larger bodies called planetesimals ("very small planets"), some of which reached diameters of several hundred kilometers. In successive stages these planetesimals coalesced into the nine planets and their numerous satellites. The rocky planets, including Earth, were near the sun, and the gaseous planets were in more distant orbits.


Young Star-CLICK to enlarge


The ages of the universe, our galaxy, the solar system, and Earth can be estimated using modern scientific methods. The age of the universe can be derived from the observed relationship between the velocities of and the distances separating the galaxies. The velocities of distant galaxies can be measured very accurately, but the measurement of distances is more uncertain. Over the past few decades, measurements of the Hubble expansion have led to estimated ages for the universe of between 7 billion and 20 billion years, with the most recent and best measurements within the range of 10 billion to 15 billion years.

The age of the Milky Way galaxy has been calculated in two ways. One involves studying the observed stages of evolution of different-sized stars in globular clusters. Globular clusters occur in a faint halo surrounding the center of the Galaxy, with each cluster containing from a hundred thousand to a million stars. The very low amounts of elements heavier than hydrogen and helium in these stars indicate that they must have formed early in the history of the Galaxy, before large amounts of heavy elements were created inside the initial generations of stars and later distributed into the interstellar medium through supernova explosions (the Big Bang itself created primarily hydrogen and helium atoms). Estimates of the ages of the stars in globular clusters fall within the range of 11 billion to 16 billion years.


Solar System


A second method for estimating the age of our galaxy is based on the present abundances of several long-lived radioactive elements in the solar system. Their abundances are set by their rates of production and distribution through exploding supernovas. According to these calculations, the age of our galaxy is between 9 billion and 16 billion years. Thus, both ways of estimating the age of the Milky Way galaxy agree with each other, and they also are consistent with the independently derived estimate for the age of the universe.

Radioactive elements occurring naturally in rocks and minerals also provide a means of estimating the age of the solar system and Earth. Several of these elements decay with half lives between 700 million and more than 100 billion years (the half life of an element is the time it takes for half of the element to decay radioactively into another element). Using these time-keepers, it is calculated that meteorites, which are fragments of asteroids, formed between 4.53 billion and 4.58 billion years ago (asteroids are small "planetoids" that revolve around the sun and are remnants of the solar nebula that gave rise to the sun and planets). The same radioactive time-keepers applied to the three oldest lunar samples returned to Earth by the Apollo astronauts yield ages between 4.4 billion and 4.5 billion years, providing minimum estimates for the time since the formation of the moon.

The oldest known rocks on Earth occur in northwestern Canada (3.96 billion years), but well-studied rocks nearly as old are also found in other parts of the world. In Western Australia, zircon crystals encased within younger rocks have ages as old as 4.3 billion years, making these tiny crystals the oldest materials so far found on Earth.


Arboreal-CLICK to enlarge


The best estimates of Earth's age are obtained by calculating the time required for development of the observed lead isotopes in Earth's oldest lead ores. These estimates yield 4.54 billion years as the age of Earth and of meteorites, and hence of the solar system.

The origins of life cannot be dated as precisely, but there is evidence that bacteria-like organisms lived on Earth 3.5 billion years ago, and they may have existed even earlier, when the first solid crust formed, almost 4 billion years ago. These early organisms must have been simpler than the organisms living today. Furthermore, before the earliest organisms there must have been structures that one would not call "alive" but that are now components of living things. Today, all living organisms store and transmit hereditary information using two kinds of molecules: DNA and RNA. Each of these molecules is in turn composed of four kinds of subunits known as nucleotides. The sequences of nucleotides in particular lengths of DNA or RNA, known as genes, direct the construction of molecules known as proteins, which in turn catalyze biochemical reactions, provide structural components for organisms, and perform many of the other functions on which life depends. Proteins consist of chains of subunits known as amino acids. The sequence of nucleotides in DNA and RNA therefore determines the sequence of amino acids in proteins; this is a central mechanism in all of biology.

Experiments conducted under conditions intended to resemble those present on primitive Earth have resulted in the production of some of the chemical components of proteins, DNA, and RNA. Some of these molecules also have been detected in meteorites from outer space and in interstellar space by astronomers using radiotelescopes. Scientists have concluded that the "building blocks of life" could have been available early in Earth's history.

An important new research avenue has opened with the discovery that certain molecules made of RNA, called ribozymes, can act as catalysts in modern cells. It previously had been thought that only proteins could serve as the catalysts required to carry out specific biochemical functions. Thus, in the early prebiotic world, RNA molecules could have been "autocatalytic"--that is, they could have replicated themselves well before there were any protein catalysts (called enzymes). Laboratory experiments demonstrate that replicating autocatalytic RNA molecules undergo spontaneous changes and that the variants of RNA molecules with the greatest autocatalytic activity come to prevail in their environments. Some scientists favor the hypothesis that there was an early "RNA world," and they are testing models that lead from RNA to the synthesis of simple DNA and protein molecules. These assemblages of molecules eventually could have become packaged within membranes, thus making up "protocells"--early versions of very simple cells.

For those who are studying the origin of life, the question is no longer whether life could have originated by chemical processes involving nonbiological components. The question instead has become which of many pathways might have been followed to produce the first cells.

Will we ever be able to identify the path of chemical evolution that succeeded in initiating life on Earth? Scientists are designing experiments and speculating about how early Earth could have provided a hospitable site for the segregation of molecules in units that might have been the first living systems. The recent speculation includes the possibility that the first living cells might have arisen on Mars, seeding Earth via the many meteorites that are known to travel from Mars to our planet.

Of course, even if a living cell were to be made in the laboratory, it would not prove that nature followed the same pathway billions of years ago. But it is the job of science to provide plausible natural explanations for natural phenomena. The study of the origin of life is a very active research area in which important progress is being made, although the consensus among scientists is that none of the current hypotheses has thus far been confirmed. The history of science shows that seemingly intractable problems like this one may become amenable to solution later, as a result of advances in theory, instrumentation, or the discovery of new facts.


The Sun-CLICK to enlarge


Creationist Views of the Origin of the Universe, Earth, and Life

Many religious persons, including many scientists, hold that God created the universe and the various processes driving physical and biological evolution and that these processes then resulted in the creation of galaxies, our solar system, and life on Earth. This belief, which sometimes is termed "theistic evolution," is not in disagreement with scientific explanations of evolution. Indeed, it reflects the remarkable and inspiring character of the physical universe revealed by cosmology, paleontology, molecular biology, and many other scientific disciplines.

The advocates of "creation science" hold a variety of viewpoints. Some claim that Earth and the universe are relatively young, perhaps only 6,000 to 10,000 years old. These individuals often believe that the present physical form of Earth can be explained by "catastrophism," including a worldwide flood, and that all living things (including humans) were created miraculously, essentially in the forms we now find them.

Other advocates of creation science are willing to accept that Earth, the planets, and the stars may have existed for millions of years. But they argue that the various types of organisms, and especially humans, could only have come about with supernatural intervention, because they show "intelligent design."

In this piece, both these "Young Earth" and "Old Earth" views are referred to as "creationism" or "special creation."

There are no valid scientific data or calculations to substantiate the belief that Earth was created just a few thousand years ago. This piece of mine has summarized the vast amount of evidence for the great age of the universe, our galaxy, the solar system, and Earth from astronomy, astrophysics, nuclear physics, geology, geochemistry, and geophysics. Independent scientific methods consistently give an age for Earth and the solar system of about 5 billion years, and an age for our galaxy and the universe that is two to three times greater. These conclusions make the origin of the universe as a whole intelligible, lend coherence to many different branches of science, and form the core conclusions of a remarkable body of knowledge about the origins and behavior of the physical world.

Nor is there any evidence that the entire geological record, with its orderly succession of fossils, is the product of a single universal flood that occurred a few thousand years ago, lasted a little longer than a year, and covered the highest mountains to a depth of several meters. On the contrary, intertidal and terrestrial deposits demonstrate that at no recorded time in the past has the entire planet been under water. Moreover, a universal flood of sufficient magnitude to form the sedimentary rocks seen today, which together are many kilometers thick, would require a volume of water far greater than has ever existed on and in Earth, at least since the formation of the first known solid crust about 4 billion years ago. The belief that Earth's sediments, with their fossils, were deposited in an orderly sequence in a year's time defies all geological observations and physical principles concerning sedimentation rates and possible quantities of suspended solid matter.

Geologists have constructed a detailed history of sediment deposition that links particular bodies of rock in the crust of Earth to particular environments and processes. If petroleum geologists could find more oil and gas by interpreting the record of sedimentary rocks as having resulted from a single flood, they would certainly favor the idea of such a flood, but they do not. Instead, these practical workers agree with academic geologists about the nature of depositional environments and geological time. Petroleum geologists have been pioneers in the recognition of fossil deposits that were formed over millions of years in such environments as meandering rivers, deltas, sandy barrier beaches, and coral reefs.

The example of petroleum geology demonstrates one of the great strengths of science. By using knowledge of the natural world to predict the consequences of our actions, science makes it possible to solve problems and create opportunities using technology. The detailed knowledge required to sustain our civilization could only have been derived through scientific investigation.

The arguments of creationists are not driven by evidence that can be observed in the natural world. Special creation or supernatural intervention is not subjectable to meaningful tests, which require predicting plausible results and then checking these results through observation and experimentation. Indeed, claims of "special creation" reverse the scientific process. The explanation is seen as unalterable, and evidence is sought only to support a particular conclusion by whatever means possible.


Colliding Worlds-CLICK to enlarge


Evidence Supporting Biological Evolution

A long path leads from the origins of primitive "life," which existed at least 3.5 billion years ago, to the profusion and diversity of life that exists today. This path is best understood as a product of evolution.

Contrary to popular opinion, neither the term nor the idea of biological evolution began with Charles Darwin and his foremost work, On the Origin of Species by Means of Natural Selection (1859). Many scholars from the ancient Greek philosophers on had inferred that similar species were descended from a common ancestor. The word "evolution" first appeared in the English language in 1647 in a nonbiological connection, and it became widely used in English for all sorts of progressions from simpler beginnings. The term Darwin most often used to refer to biological evolution was "descent with modification," which remains a good brief definition of the process today.

Darwin proposed that evolution could be explained by the differential survival of organisms following their naturally occurring variation--a process he termed "natural selection." According to this view, the offspring of organisms differ from one another and from their parents in ways that are heritable--that is, they can pass on the differences genetically to their own offspring. Furthermore, organisms in nature typically produce more offspring than can survive and reproduce given the constraints of food, space, and other environmental resources. If a particular off spring has traits that give it an advantage in a particular environment, that organism will be more likely to survive and pass on those traits. As differences accumulate over generations, populations of organisms diverge from their ancestors.

Darwin's original hypothesis has undergone extensive modification and expansion, but the central concepts stand firm. Studies in genetics and molecular biology--fields unknown in Darwin's time--have explained the occurrence of the hereditary variations that are essential to natural selection. Genetic variations result from changes, or mutations, in the nucleotide sequence of DNA, the molecule that genes are made from. Such changes in DNA now can be detected and described with great precision.

Genetic mutations arise by chance. They may or may not equip the organism with better means for surviving in its environment. But if a gene variant improves adaptation to the environment (for example, by allowing an organism to make better use of an available nutrient, or to escape predators more effectively--such as through stronger legs or disguising coloration), the organisms carrying that gene are more likely to survive and reproduce than those without it. Over time, their descendants will tend to increase, changing the average characteristics of the population. Although the genetic variation on which natural selection works is based on random or chance elements, natural selection itself produces "adaptive" change--the very opposite of chance.


An essential duo: Einstein & Darwin


Scientists also have gained an understanding of the processes by which new species originate. A new species is one in which the individuals cannot mate and produce viable descendants with individuals of a preexisting species. The split of one species into two often starts because a group of individuals becomes geographically separated from the rest. This is particularly apparent in distant remote islands, such as the Galápagos and the Hawaiian archipelago, whose great distance from the Americas and Asia means that arriving colonizers will have little or no opportunity to mate with individuals remaining on those continents. Mountains, rivers, lakes, and other natural barriers also account for geographic separation between populations that once belonged to the same species.

Once isolated, geographically separated groups of individuals become genetically differentiated as a consequence of mutation and other processes, including natural selection. The origin of a species is often a gradual process, so that at first the reproductive isolation between separated groups of organisms is only partial, but it eventually becomes complete. Scientists pay special attention to these intermediate situations, because they help to reconstruct the details of the process and to identify particular genes or sets of genes that account for the reproductive isolation between species.

A particularly compelling example of speciation involves the 13 species of finches studied by Darwin on the Galápagos Islands, now known as Darwin's finches. The ancestors of these finches appear to have emigrated from the South American mainland to the Galápagos. Today the different species of finches on the island have distinct habitats, diets, and behaviors, but the mechanisms involved in speciation continue to operate. A research group led by Peter and Rosemary Grant of Princeton University has shown that a single year of drought on the islands can drive evolutionary changes in the finches. Drought diminishes supplies of easily cracked nuts but permits the survival of plants that produce larger, tougher nuts. Droughts thus favor birds with strong, wide beaks that can break these tougher seeds, producing populations of birds with these traits. The Grants have estimated that if droughts occur about once every 10 years on the islands, a new species of finch might arise in only about 200 years.

The following sections consider several aspects of biological evolution in greater detail, looking at paleontology, comparative anatomy, biogeography, embryology, and molecular biology for further evidence supporting evolution.


Galaxy - CLICK to enlarge


The Fossil Record

Although it was Darwin, above all others, who first marshalled convincing evidence for biological evolution, earlier scholars had recognized that organisms on Earth had changed systematically over long periods of time. For example, in 1799 an engineer named William Smith reported that, in undisrupted layers of rock, fossils occurred in a definite sequential order, with more modern-appearing ones closer to the top. Because bottom layers of rock logically were laid down earlier and thus are older than top layers, the sequence of fossils also could be given a chronology from oldest to youngest. His findings were confirmed and extended in the 1830s by the paleontologist William Lonsdale, who recognized that fossil remains of organisms from lower strata were more primitive than the ones above. Today, many thousands of ancient rock deposits have been identified that show corresponding successions of fossil organisms.

Thus, the general sequence of fossils had already been recognized before Darwin conceived of descent with modification. But the paleontologists and geologists before Darwin used the sequence of fossils in rocks not as proof of biological evolution, but as a basis for working out the original sequence of rock strata that had been structurally disturbed by earthquakes and other forces.

In Darwin's time, paleontology was still a rudimentary science. Large parts of the geological succession of stratified rocks were unknown or inadequately studied.

Darwin, therefore, worried about the rarity of intermediate forms between some major groups of organisms.

Today, many of the gaps in the paleontological record have been filled by the research of paleontologists. Hundreds of thousands of fossil organisms, found in well-dated rock sequences, represent successions of forms through time and manifest many evolutionary transitions. As mentioned earlier, microbial life of the simplest type was already in existence 3.5 billion years ago. The oldest evidence of more complex organisms (that is, eucaryotic cells, which are more complex than bacteria) has been discovered in fossils sealed in rocks approximately 2 billion years old. Multicellular organisms, which are the familiar fungi, plants, and animals, have been found only in younger geological strata. The following list presents the order in which increasingly complex forms of life appeared:

----------------------------------------------------------------

Life Forms & Millions of Years Since First Known Appearance
(Approximate)
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Microbial (procaryotic cells)........ 3,500
Complex (eucaryotic cells)......... 2,000
First multicellular animals............ 670
Shell-bearing animals................. 540
Vertebrates (simple fishes)......... 490
Amphibians.............................. 350
Reptiles.................................. 310
Mammals................................ 200
Nonhuman primates................... 60
Earliest apes............................ 25
Australopithecine....................... 4 [ancestors of humans]
Modern humans........................ 0.15 (150,000 years)

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Cosmos - CLICK to enlarge


So many intermediate forms have been discovered between fish and amphibians, between amphibians and reptiles, between reptiles and mammals, and along the primate lines of descent that it often is difficult to identify categorically when the transition occurs from one to another particular species. Actually, nearly all fossils can be regarded as intermediates in some sense; they are life forms that come between the forms that preceded them and those that followed.

The fossil record thus provides consistent evidence of systematic change through time--of descent with modification. From this huge body of evidence, it can be predicted that no reversals will be found in future paleontological studies. That is, amphibians will not appear before fishes, nor mammals before reptiles, and no complex life will occur in the geological record before the oldest eucaryotic cells. This prediction has been upheld by the evidence that has accumulated until now: no reversals have been found.

Common Structures

Inferences about common descent derived from paleontology are reinforced by comparative anatomy. For example, the skeletons of humans, mice, and bats are strikingly similar, despite the different ways of life of these animals and the diversity of environments in which they flourish. The correspondence of these animals, bone by bone, can be observed in every part of the body, including the limbs; yet a person writes, a mouse runs, and a bat flies with structures built of bones that are different in detail but similar in general structure and relation to each other.

Scientists call such structures homologies and have concluded that they are best explained by common descent. Comparative anatomists investigate such homologies, not only in bone structure but also in other parts of the body, working out relationships from degrees of similarity. Their conclusions provide important inferences about the details of evolutionary history, inferences that can be tested by comparisons with the sequence of ancestral forms in the paleontological record.

The mammalian ear and jaw are instances in which paleontology and comparative anatomy combine to show common ancestry through transitional stages. The lower jaws of mammals contain only one bone, whereas those of reptiles have several. The other bones in the reptile jaw are homologous with bones now found in the mammalian ear. Paleontologists have discovered intermediate forms of mammal-like reptiles (Therapsida) with a double jaw joint--one composed of the bones that persist in mammalian jaws, the other consisting of bones that eventually became the hammer and anvil of the mammalian ear.


Ocean Life - CLICK to enlarge


The Distribution of Species

Biogeography also has contributed evidence for descent from common ancestors. The diversity of life is stupendous. Approximately 250,000 species of living plants, 100,000 species of fungi, and one million species of animals have been described and named, each occupying its own peculiar ecological setting or niche; and the census is far from complete. Some species, such as human beings and our companion the dog, can live under a wide range of environments. Others are amazingly specialized. One species of a fungus (Laboulbenia) grows exclusively on the rear portion of the covering wings of a single species of beetle (Aphaenops cronei) found only in some caves of southern France. The larvae of the fly Drosophila carcinophila can develop only in specialized grooves beneath the flaps of the third pair of oral appendages of a land crab that is found only on certain Caribbean islands.

How can we make intelligible the colossal diversity of living beings and the existence of such extraordinary, seemingly whimsical creatures as the fungus, beetle, and fly described above? And why are island groups like the Galápagos so often inhabited by forms similar to those on the nearest mainland but belonging to different species? Evolutionary theory explains that biological diversity results from the descendants of local or migrant predecessors becoming adapted to their diverse environments. This explanation can be tested by examining present species and local fossils to see whether they have similar structures, which would indicate how one is derived from the other. Also, there should be evidence that species without an established local ancestry had migrated into the locality.


Porcupine in full bloom!

Wherever such tests have been carried out, these conditions have been confirmed. A good example is provided by the mammalian populations of North and South America, where strikingly different native organisms evolved in isolation until the emergence of the isthmus of Panama approximately 3 million years ago. Thereafter, the armadillo, porcupine, and opossum -- mammals of South American origin -- migrated north, along with many other species of plants and animals, while the mountain lion and other North American species made their way across the isthmus to the south.

The evidence that Darwin found for the influence of geographical distribution on the evolution of organisms has become stronger with advancing knowledge. For example, approximately 2,000 species of flies belonging to the genus Drosophila are now found throughout the world. About one-quarter of them live only in Hawaii. More than a thousand species of snails and other land mollusks also are found only in Hawaii. The biological explanation for the multiplicity of related species in remote localities is that such great diversity is a consequence of their evolution from a few common ancestors that colonized an isolated environment. The Hawaiian Islands are far from any mainland or other islands, and on the basis of geological evidence they never have been attached to other lands. Thus, the few colonizers that reached the Hawaiian Islands found many available ecological niches, where they could, over numerous generations, undergo evolutionary change and diversification. No mammals other than one bat species lived in the Hawaiian Islands when the first human settlers arrived; similarly, many other kinds of plants and animals were absent.

The Hawaiian Islands are not less hospitable than other parts of the world for the absent species. For example, pigs and goats have multiplied in the wild in Hawaii, and other domestic animals also thrive there. The scientific explanation for the absence of many kinds of organisms, and the great multiplication of a few kinds, is that many sorts of organisms never reached the islands, because of their geographic isolation. Those that did reach the islands diversified over time because of the absence of related organisms that would compete for resources.

Similarities During Development

Embryology, the study of biological development from the time of conception, is another source of independent evidence for common descent. Barnacles, for instance, are sedentary crustaceans with little apparent similarity to such other
crustaceans as lobsters, shrimps, or copepods. Yet barnacles pass through a free-swimming larval stage in which they look like other crustacean larvae. The similarity of larval stages supports the conclusion that all crustaceans have homologous parts and a common ancestry.

Similarly, a wide variety of organisms from fruit flies to worms to mice to humans have very similar sequences of genes that are active early in development. These genes influence body segmentation or orientation in all these diverse groups. The presence of such similar genes doing similar things across such a wide range of organisms is best explained by their having been present in a very early common ancestor of all of these groups.


Ending - CLICK to enlarge


New Evidence from Molecular Biology

The unifying principle of common descent that emerges from all the foregoing lines of evidence is being reinforced by the discoveries of modern biochemistry and molecular biology.

The code used to translate nucleotide sequences into amino acid sequences is essentially the same in all organisms. Moreover, proteins in all organisms are invariably composed of the same set of 20 amino acids. This unity of composition and function is a powerful argument in favor of the common descent of the most diverse organisms.

In 1959, scientists at Cambridge University in the UK determined the three-dimensional structures of two proteins that are found in almost every multicelled animal: hemoglobin and myoglobin. Hemoglobin is the protein that carries oxygen in the blood. Myoglobin receives oxygen from hemoglobin and stores it in the tissues until needed. These were the first three-dimensional protein structures to be solved, and they yielded some key insights. Myoglobin has a single chain of 153 amino acids wrapped around a group of iron and other atoms (called "heme") to which oxygen binds. Hemoglobin, in contrast, is made of up four chains: two identical chains consisting of 141 amino acids, and two other identical chains consisting of 146 amino acids. However, each chain has a heme exactly like that of myoglobin, and each of the four chains in the hemoglobin molecule is folded exactly like myoglobin. It was immediately obvious in 1959 that the two molecules are very closely related.

During the next two decades, myoglobin and hemoglobin sequences were determined for dozens of mammals, birds, reptiles, amphibians, fish, worms, and molluscs. All of these sequences were so obviously related that they could be compared with confidence with the three-dimensional structures of two selected standards--whale myoglobin and horse hemoglobin. Even more significantly, the differences between sequences from different organisms could be used to construct a family tree of hemoglobin and myoglobin variation among organisms. This tree agreed completely with observations derived from paleontology and anatomy about the common descent of the corresponding organisms.

Similar family histories have been obtained from the three-dimensional structures and amino acid sequences of other proteins, such as cytochrome c (a protein engaged in energy transfer) and the digestive proteins trypsin and chymotrypsin. The examination of molecular structure offers a new and extremely powerful tool for studying evolutionary relationships. The quantity of information is potentially huge -- as large as the thousands of different proteins contained in living organisms, and limited only by the time and resources of molecular biologists.


DNA structure

As the ability to sequence the nucleotides making up DNA has improved, it also has become possible to use genes to reconstruct the evolutionary history of organisms. Because of mutations, the sequence of nucleotides in a gene gradually changes over time. The more closely related two organisms are, the less different their DNA will be. Because there are tens of thousands of genes in humans and other organisms, DNA contains a tremendous amount of information about the evolutionary history of each organism.

Genes evolve at different rates because, although mutation is a random event, some proteins are much more tolerant of changes in their amino acid sequence than are other proteins. For this reason, the genes that encode these more tolerant, less constrained proteins evolve faster. The average rate at which a particular kind of gene or protein evolves gives rise to the concept of a "molecular clock." Molecular clocks run rapidly for less constrained proteins and slowly for more constrained proteins, though they all time the same evolutionary events.

The figure on this page compares three molecular clocks: for cytochrome c proteins, which interact intimately with other macromolecules and are quite constrained in their amino acid sequences; for the less rigidly constrained hemoglobins, which interact mainly with oxygen and other small molecules; and for fibrinopeptides, which are protein fragments that are cut from larger proteins (fibrinogens) when blood clots. The clock for fibrinopeptides runs rapidly; 1 percent of the amino acids change in a little longer than 1 million years. At the other extreme, the molecular clock runs slowly for cytochrome c; a 1 percent change in amino acid sequence requires 20 million years. The hemoglobin clock is intermediate.

The concept of a molecular clock is useful for two purposes. It determines evolutionary relationships among organisms, and it indicates the time in the past when species started to diverge from one another. Once the clock for a particular gene or protein has been calibrated by reference to some event whose time is known, the actual chronological time when all other events occurred can be determined by examining the protein or gene tree.

An interesting additional line of evidence supporting evolution involves sequences of DNA known as "pseudogenes." Pseudogenes are remnants of genes that no longer function but continue to be carried along in DNA as excess baggage. Pseudogenes also change through time, as they are passed on from ancestors to descendants, and they offer an especially useful way of reconstructing evolutionary relationships.

With functioning genes, one possible explanation for the relative similarity between genes from different organisms is that their ways of life are similar -- for example, the genes from a horse and a zebra could be more similar because of their similar habitats and behaviours than the genes from a horse and a tiger. But this possible explanation does not work for pseudogenes, since they perform no function. Rather, the degree of similarity between pseudogenes must simply reflect their evolutionary relatedness. The more remote the last common ancestor of two organisms, the more dissimilar their pseudogenes will be.


Whale breaking

The evidence for evolution from molecular biology is overwhelming and is growing quickly. In some cases, this molecular evidence makes it possible to go beyond the paleontological evidence. For example, it has long been postulated that whales descended from land mammals that had returned to the sea. From anatomical and paleontological evidence, the whales' closest living land relatives seemed to be the even-toed hoofed mammals (modern cattle, sheep, camels, goats, etc.). Recent comparisons of some milk protein genes (beta-casein and kappa-casein) have confirmed this relationship and have suggested that the closest land-bound living relative of whales may be the hippopotamus. In this case, molecular biology has augmented the fossil record.

Creationism and the Evidence for Evolution

Some creationists cite what they say is an incomplete fossil record as evidence for the failure of evolutionary theory. The fossil record was incomplete in Darwin's time, but many of the important gaps that existed then have been filled by subsequent paleontological research. Perhaps the most persuasive fossil evidence for evolution is the consistency of the sequence of fossils from early to recent. Nowhere on

Earth do we find, for example, mammals in Devonian (the age of fishes) strata, or human fossils coexisting with dinosaur remains. Undisturbed strata with simple unicellular organisms predate those with multicellular organisms, and invertebrates precede vertebrates; nowhere has this sequence been found inverted. Fossils from adjacent strata are more similar than fossils from temporally distant strata. The most reasonable scientific conclusion that can be drawn from the fossil record is that descent with modification has taken place as stated in evolutionary theory.

Special creationists argue that "no one has seen evolution occur." This misses the point about how science tests hypotheses. We don't see Earth going around the sun or the atoms that make up matter. We "see" their consequences. Scientists infer that atoms exist and Earth revolves because they have tested predictions derived from these concepts by extensive observation and experimentation.

Furthermore, on a minor scale, we "experience" evolution occurring every day. The annual changes in influenza viruses and the emergence of antibiotic-resistant bacteria are both products of evolutionary forces. Indeed, the rapidity with which organisms with short generation times, such as bacteria and viruses, can evolve under the influence of their environments is of great medical significance. Many laboratory experiments have shown that, because of mutation and natural selection, such microorganisms can change in specific ways from those of immediately preceding generations.

On a larger scale, the evolution of mosquitoes resistant to insecticides is another example of the tenacity and adaptability of organisms under environmental stress. Similarly, malaria parasites have become resistant to the drugs that were used extensively to combat them for many years. As a consequence, malaria is on the increase, with more than 300 million clinical cases of malaria occurring every year.


human eye

Molecular evolutionary data counter a recent proposition called "intelligent design theory." Proponents of this idea argue that structural complexity is proof of the direct hand of God in specially creating organisms as they are today. These arguments echo those of the 18th century cleric William Paley who held that the vertebrate eye, because of its intricate organization, had been specially designed in its present form by an omnipotent Creator. Modern-day intelligent design proponents argue that molecular structures such as DNA, or molecular processes such as the many steps that blood goes through when it clots, are so irreducibly complex that they can function only if all the components are operative at once. Thus, proponents of intelligent design say that these structures and processes could not have evolved in the stepwise mode characteristic of natural selection.

However, structures and processes that are claimed to be "irreducibly" complex typically are not on closer inspection. For example, it is incorrect to assume that a complex structure or biochemical process can function only if all its components are present and functioning as we see them today. Complex biochemical systems can be built up from simpler systems through natural selection. Thus, the "history" of a protein can be traced through simpler organisms. Jawless fish have a simpler hemoglobin than do jawed fish, which in turn have a simpler hemoglobin than mammals.

The evolution of complex molecular systems can occur in several ways. Natural selection can bring together parts of a system for one function at one time and then, at a later time, recombine those parts with other systems of components to produce a system that has a different function. Genes can be duplicated, altered, and then amplified through natural selection. The complex biochemical cascade resulting in blood clotting has been explained in this fashion.

Similarly, evolutionary mechanisms are capable of explaining the origin of highly complex anatomical structures. For example, eyes may have evolved independently many times during the history of life on Earth. The steps proceed from a simple eye spot made up of light-sensitive retinula cells (as is now found in the flatworm), to formation of individual photosensitive units (ommatidia) in insects with light focusing lenses, to the eventual formation of an eye with a single lens focusing images onto a retina. In humans and other vertebrates, the retina consists not only of photoreceptor cells but also of several types of neurons that begin to analyze the visual image. Through such gradual steps, very different kinds of eyes have evolved, from simple light-sensing organs to highly complex systems for vision.


Infinity - CLICK to enlarge


Human Evolution

Studies in evolutionary biology have led to the conclusion that human beings arose from ancestral primates. This association was hotly debated among scientists in Darwin's day. But today there is no significant scientific doubt about the close evolutionary relationships among all primates, including humans.

Many of the most important advances in paleontology over the past century relate to the evolutionary history of humans. Not one but many connecting links -- intermediate between and along various branches of the human family tree -- have been found as fossils. These linking fossils occur in geological deposits of intermediate age. They document the time and rate at which primate and human evolution occurred.

Scientists have unearthed thousands of fossil specimens representing members of the human family. A great number of these cannot be assigned to the modern human species, Homo sapiens. Most of these specimens have been well dated, often by means of radiometric techniques. They reveal a well-branched tree, parts of which trace a general evolutionary sequence leading from ape-like forms to modern humans.

Australopithecus Africanus Paleontologists have discovered numerous species of extinct apes in rock strata that are older than four million years, but never a member of the human family at that great age. Australopithecus, whose earliest known fossils are about four million years old, is a genus with some features closer to apes and some closer to modern humans. In brain size, Australopithecus was barely more advanced than apes. A number of features, including long arms, short legs, intermediate toe structure, and features of the upper limb, indicate that the members of this species spent part of the time in trees. But they also walked upright on the ground, like humans. Bipedal tracks of Australopithecus have been discovered, beautifully preserved with those of other extinct animals, in hardened volcanic ash. Most of our Australopithecus ancestors died out close to two-and-a-half million years ago, while other Australopithecus species, which were on side branches of the human tree, survived alongside more advanced hominids for another million years.

Trackways made by Australopithecus in volcanic ash: about 4 m.y. oldDistinctive bones of the oldest species of the human genus, Homo, date back to rock strata about 2.4 million years old. Physical anthropologists agree that Homo evolved from one of the species of Australopithecus. By two million years ago, early members of Homo had an average brain size one-and-a-half times larger than that of Australopithecus, though still substantially smaller than that of modern humans. The shapes of the pelvic and leg bones suggest that these early Homo were not part-time climbers like Australopithecus but walked and ran on long legs, as modern humans do. Just as Australopithecus showed a complex of ape-like, human-like, and intermediate features, so was early Homo intermediate between Australopithecus and modern humans in some features, and close to modern humans in other respects. The earliest stone tools are of virtually the same age as the earliest fossils of Homo. Early Homo, with its larger brain than Australopithecus, was a maker of stone tools.

The fossil record for the interval between 2.4 million years ago and the present includes the skeletal remains of several species assigned to the genus Homo. The more recent species had larger brains than the older ones. This fossil record is complete enough to show that the human genus first spread from its place of origin in Africa to Europe and Asia a little less than two million years ago. Distinctive types of stone tools are associated with various populations. More recent species with larger brains generally used more sophisticated tools than more ancient species.

Molecular biology also has provided strong evidence of the close relationship between humans and apes. Analysis of many proteins and genes has shown that humans are genetically similar to chimpanzees and gorillas and less similar to orangutans and other primates.

Neanderthal skullDNA has even been extracted from a well-preserved skeleton of the extinct human creature known as Neanderthal, a member of the genus Homo and often considered either as a subspecies of Homo sapiens or as a separate species. Application of the molecular clock, which makes use of known rates of genetic mutation, suggests that Neanderthal's lineage diverged from that of modern Homo sapiens less than half a million years ago, which is entirely compatible with evidence from the fossil record.

Based on molecular and genetic data, evolutionists favor the hypothesis that modern Homo sapiens, individuals very much like us, evolved from more archaic humans about 100,000 to 150,000 years ago. They also believe that this transition occurred in Africa, with modern humans then dispersing to Asia, Europe, and eventually Australasia and the Americas.

Discoveries of hominid remains during the past three decades in East and South Africa, the Middle East, and elsewhere have combined with advances in molecular biology to initiate a new discipline--molecular paleoanthropology. This field of inquiry is providing an ever-growing inventory of evidence for a genetic affinity between human beings and the African apes.

Opinion polls show that many people believe that divine intervention actively guided the evolution of human beings. Science cannot comment on the role that supernatural forces might play in human affairs. But scientific investigations have concluded that the same forces responsible for the evolution of all other life forms on Earth can account for the evolution of human beings.


Uhmmm...er...yeah


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Wikilink
~ Main e-reference: Wikipedia (thank you, Wiki!)



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So then, here's how life originated

Ta-taaaa: The Origin of Life!
[N.B.: Here and now I admit that I have a direct line with God]

The Problem

The question to be considered here is not how living bodies originate now. With respect to the present everyone admits biogenesis as a law, i.e., not a single instance is known of a living body which did not come into existence through a process of generation from another living body. The experiments of Pasteur and others have conclusively shown that in all instances where life seemed to originate from inanimate matter, microscopically small organisms gave rise to the new living bodies.

Our problem is concerned with the possibility of living bodies originating from inanimate matter. To a certain extent this problem refers to the future, but its main interest lies still in the past. It refers to the future insofar as the question can be raised whether or not laboratory experiments will ever succeed in producing a living organism, no matter how primitive, from inanimate matter. It refers to the past insofar as all available evidence points to the fact that once life on earth was physically impossible, so that at some time in the distant past living bodies must have made their first appearance on earth. Because observation of this first appearance is evidently impossible, the question how this life originated may be studied philosophically by an investigation of the various possibilities and the elimination of any position that is not in accordance with reason. In this way it will perhaps be possible to arrive at the conclusion that only one position is in agreement with the demands of reason, or that one position offers a great degree of probability than others.

Possible Positions Concerning the Origin of Life

Omitting pantheistic and occasionalistic hypotheses with respect to the origin of life, the following may be formulated:


  • 1. Living bodies did not originate in time, but have always existed.


  • 2. The first living bodies came to the earth from other planets.


  • 3. The first living bodies were created directly by God. By direct creation is meant that God produced from nothing both body and soul of the first living bodies.


  • 4. The first living bodies were produced by God's positive intervention in the existing order of nature. Suspending the laws of nature, He directly produced in inanimate matter the conditions which made matter proximately disposed for actuation by a soul. This soul was educed from the potency of matter, except in the case of man, whose soul was created directly by God.


  • 5. Living bodies can be produced from inanimate matter by the sole forces of matter, without any influence of extraneous causes. In this hypothesis, physical and chemical reactions are considered to be the adequate explanation for the origin of life.


  • 6. Living bodies can originate from inanimate matter under the influence of the Primary Cause (God), acting through causes that are intrinsic to matter.


  • 7. Living bodies can originate from inanimate matter under the influence of a secondary cause, extraneous to matter, acting upon inanimate matter.
  • Michelangelo's Creation: CLICK to enlarge
    Examination of the Various Positions with Respect to the Origin of Life
    The first two of these positions need not be considered to any great extent. Even if living bodies had always existed they would need a cause to explain their existence, for their essence is not their "to be," and therefore, they do not have in themselves a sufficient reason for their existence. Moreover, the earth has not always been suitable for life, because at one time in the past it was so hot that no living bodies could have existed upon it. To explain the origin of living bodies by claiming that they came form other planets, as is done by the second position, merely shifts the problem to another planet. Moreover, in passing from another planet to the earth, any form of physical life would have been exposed to certain death because of ultraviolet rays and the heat resulting from its passage through the atmosphere.

    Direct Creation. There cannot be any doubt concerning the possibility that living bodies were directly created by God, for anything which is not a contradiction in terms can be done by God. The point, however, is that it would be unreasonable to suppose that God created new bodies when plenty of matter was available for the formation of these bodies. It does not seem in accordance with wisdom to make new material where an abundance of suitable material is available. But inanimate matter contains all the necessary material for the physical organization required by a living body.

    Divine Intervention as the Sole Organizing Cause of Matter. Again, there cannot be any doubt that God has the power directly to organize matter in such a way that it is immediately disposed for actuation by a soul. However, it would seem unreasonable to attribute directly to God what can be brought about through the activity of the natural forces of inanimate matter acting in accordance with the laws of nature. If the Author of nature has endowed matter with forces that can naturally lead to the emergence of living bodies, it would seem unreasonable to suppose that He positively intervened in the process of natural development by suspending the activity of these forces and directly organizing inanimate matter. We say if, for it remains to be seen whether or not living bodies can have originated from inanimate matter acting in accordance with the laws of nature. Should the answer to this question be negative, then it would seem to be more consonant with divine wisdom to give rise to living bodies by organizing existing matter than by the creation of new matter.

    Emergence of Life from Matter Alone. Can the physical forces of inanimate matter alone serve as an adequate explanation for the emergence of life? At first sight it would seem that the forces of inanimate matter can never give rise to a living body, because any material cause acts in accordance with its nature and therefore its effect cannot be greater than itself. But a living body is essentially more perfect than a nonliving body; hence it would seem that no forces of inanimate matter can give rise to a living body.

    However, this answer fails to take into consideration the possibility of many material causes combining to produce an effect. Admittedly, if it is possible to introduce into a body the material dispositions making it proximately disposed for actuation by a soul, the cause or causes introducing these dispositions are the cause of a living body. The question, therefore, is whether or not it would be impossible for a combination of material forces to cause these dispositions in nonliving matter. The enormous complexity of the necessary dispositions excludes the possibility that a single line of material causality would ever produce these dispositions. But it is a well-known fact that physical causality, as it occurs in nature, is a very complex process in which many different lines of causality constantly interfere with one another.

    Now the interference of different lines of causality may result in an effect which is proportioned to none of the interfering causes taken separately. Conceivably such an effect could be even more perfect than any of the producing causes, precisely because the combination of these causes could happen to be equal to the material causality normally exercised by one cause of a higher nature. If the material forces operating in a living body, which the soul combines into a single unit, are able to cause the necessary dispositions for life and thus produce a new living body, why would it be impossible for these forces to be united "by chance" into an operational unit and thus give rise to a living body? If such a thing did happen a living body would have been produced from inanimate matter. Thus it would not be impossible for a combination of inanimate forces to give rise to a living body.

    Granted that such a combination is a possibility, does it provide an adequate explanation for the origin of life? An adequate explanation is one which takes into consideration all the causes that are at work in the production of an effect. No one admits that in the present state of science it is possible to indicate even all the physical forces that are necessary for the production of the dispositions of matter required for actuation by a soul. But supposing that a time will come when man will know all the material causes whose combination results in the production of a living body, will he have an adequate explanation for the origin of living bodies? The answer is in the negative, because he has failed to indicate the cause which led to the combination of these causes by unifying their activity.

    But could not this unification be brought about by chance, as was suggested above? We must answer that an appeal to chance is not an explanation. Chance refers to the unpredictability of an effect produced by causes whose combined action cannot be foreseen, because the cause of their combination is not known. To deny that their combination has a cause is tantamount to a denial of the principle of causality. Therefore, an appeal to chance is an admission that the known physical forces of inanimate matter cannot explain the origin of life.

    But, perhaps, at a future date science will discover the cause or causes which combine the forces of inanimate matter and make them produce in a nonliving body the necessary dispositions for actuation by a soul. Then, at least, science will have given an adequate explanation for the emergence of life by the sole forces of inanimate matter. Again, however, our answer has to be in the negative. Granted that perhaps a material agent causing the unification of these forces will be discovered, there still remains the principle of finality, i.e., the metaphysical law that every agent acts for a definite purpose. An agent can act for a purpose either because it is made to act for this purpose by an intelligent being, or because the agent himself is an intelligent being and directs his activity to a definite end.

    If the cause of the unification is purely material, it cannot be an intelligent agent; therefore it acts towards a purpose merely because it is made to act in this way by an intelligent being. This intelligent being, qua intelligent, is extraneous to matter, for any intellect is immaterial. If, on the other hand, the agent is immaterial, it is of course extraneous to matter. Our final conclusion, therefore, is that the physical forces of inanimate matter alone cannot give an adequate explanation for the origin of living bodies.

    Emergence of Life from Matter Under the Directing Influence of God. This position combines certain aspects of the two preceding hypotheses and discards others. It agrees with the theory of divine intervention insofar as it demands God's influence upon matter in the production of living bodies; it differs from it in that it does not require a suspension of the deterministic laws of nature (a miraculous intervention), but merely that God act through causes which are intrinsic to matter.

    It agrees with the theory that life originates from matter alone insofar as it admits that the physical forces of inanimate matter can produce life, but differs from it because it requires that these causes be directed by the Primary Cause. Does this new position offer a satisfactory explanation for the origin of living bodies?

    There is no reason to suppose that God cannot exercise influence upon the forces of inanimate matter without suspending the deterministic laws of nature. All that is necessary is that God make use of the intrinsic forces of matter, which act in accordance with these laws, by directing their activity to the purpose He intends, viz., the production of the necessary conditions for the actuation of matter by a soul. The question, however, is whether God can give such a direction to the forces of matter without producing in existing matter a tendency previously nonexistent in it, for such a production would be a positive intervention in the existing order of nature.

    To this question, we answer that the existence of such a tendency in matter allows a double explanation -- either God created it in matter which previously did not have it, or He concreated it in matter when matter itself was created. In the first case there would have been a positive intervention, and the whole explanation would be identical with the position that the divine Cause organizes matter by suspending the existing laws of nature. In the second alternative, however, this tendency would belong to the very essence of the material world, as planned and created by God.

    Therefore, the directing influence of this tendency would not be an intervention in the established order of nature, but merely the execution of the order of nature established by divine providence. In this theory inanimate matter from its very beginning would have possessed all the forces necessary for the emergence of life, because God Himself planned the whole course of nature in such a way that life followed of necessity when the planned combination of inanimate forces occurred.

    If this position were true the human observer of nature would be faced with effects emerging "by chance" from a concurrence of causes, because he does not see this concurrence takes place according to plan. Consequently, upon his level of explanation, he would be justified in speaking about life as emerging from a chance meeting of inanimate causes. He would be mistaken, however, if from his observations he would conclude that his explanation gives an adequate account for the origin of life.

    It would seem that this theory does not violate any physical or metaphysical principles. Although it does not postulate a special intervention of God in the origin of life, it does not deny that life could originate only as a result of God's planning and providence. It certainly would be a more splendid manifestation of God's power if life were produced in this way rather than by a miraculous intervention in the established order of nature.

    Emergence of Life from Matter Under the Directing Influence of a Secondary Cause. If the preceding theory offers an explanation for the emergence of life, there seems to be no reason why it should be impossible for an intelligent secondary cause to direct the forces of matter in the production of the material conditions required for actuation by a soul. Of course, such a cause would need to have a far greater knowledge of matter than is possessed by man at this time. It would not seem impossible, however, that ultimately man will succeed in acquiring this knowledge and be able to utilize it to obtain the desired effect. In that case man would be able to produce living bodies artificially. Nevertheless, it would not be a case of life being produced by the sole forces of matter, because these forces would be under the direction of man, who is an intelligent being. Moreover, even in this case God's action would not be excluded, because man's activity does not escape the directing influence of God.

    A similar theory for the emergence of life from inanimate matter was offered by ancient and medieval philosophers, including St Thomas, as an explanation of the supposedly spontaneous generation of maggots in decaying flesh. They though that in this case the forces of inanimate matter, as acted upon by the sun or other celestial bodies under the direction of spiritual substances, made matter proximately disposed for actuation of a soul.

    Conclusion

    Of the seven positions formulated above with respect to the first origin of life only the third, fourth, sixth, and seventh offer reasonable possibilities. However, the third (direct creation of the whole living body) is less probable, although it cannot be called impossible. The seventh (directing influence of a secondary cause) does not apply to the first origin of living bodies, if man is supposed to be this cause. Hence, the choice seems to be mainly between the fourth position (God as the sole organizing cause of matter) and the sixth (emergence of life under the influence of God acting through causes that are intrinsic to matter). Of course, it is impossible to say what actually did happen, unless there is a reliable report of a witness. But if there is such a report, its contents escape from the domain of philosophy and physical science.

    Do YOU have the report?



    ~ ~ ~ ~ ~ ~ ~


    Historical Notes

    The eternal existence of living bodies was defended by Arrhenius (1859-1927), Preyer (1831-1897), and a few others. Keyserling (born 1880), Lord Kelvin (1827-1907), and Helmholtz (1821-1894) held that the first germs of life on earth had come from outer space. Most authors who defend the eternal existence of living bodies combine the second position with the first.

    The origin of "imperfect animals" from inanimate matter under the influence of celestial bodies, as directed by spiritual substances, was commonly admitted before the experiments of Pasteur (1822-1895). Avicenna admitted the possibility of such an origin even with respect to "perfect animals."

    Direct creation of the first living bodies with respect to both body and soul was favored by Remer, while others (Gredt) were more inclined to admit divine intervention as the sole organizing cause of matter.

    The possibility of life emerging from causes intrinsic to matter under God's directive influence is regarded with favor by many contemporary Thomists, such as Sertillanges, Messenger, Brennan, and Klubertanz.

    The emergence of life from matter alone is the view taken by many materialistic evolutionists, such as Haeckel and Huxley.

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    Regurgitating World History




    Developing Historical Formats

    Einstein and history...?


    Histories of the portion of the earth known to the writer are properly classed as world histories inasmuch as they seek to record the whole significant and knowable past. By that standard, therefore, Herodotus and Ssuma Ch'ien were world historians as well as founders of their respective historiographical traditions. Among the Greeks, however, Thucydides promptly discarded Herodotus' discursive, all-embracing approach to history, offering instead a pridefully accurate, sharply focused monograph, dealing with twenty seven years of war between Athens and Sparta.

    These alternative models remained normative throughout Greco-Roman antiquity. Livy's vast, patriotic history of Rome approximated Herodotean inclusiveness; and Polybius may have deliberately aspired to combine the logical rigor of Thucydides with the scope of Herodotus. Though impossible to equal, Thucydides' precision was easier to imitate than Herodotus' inclusiveness, and most Greco-Roman historians accordingly inclined towards the monographic, political-military focus that Thucydides so magnificently exemplified.

    Jewish sacred scripture elaborated a different historical vision, according to which Almighty God governed all peoples, everywhere, whether they knew it or not. For about a millennium, defeats suffered by successive Jewish states made such a vision of human history implausible to unbelievers; but Christianity, when it emerged to dominance within the Roman empire in the fourth century A.D., brought to the fore a modified, expanded, but fundamentally Jewish, and entirely God- centered, view of history. Christians subordinated secular pagan to sacred Biblical history, and thereby reversed the balance between Herodotean and Thucididean formats for history, since, from Jewish and Christian points of view, all history was world history, being part of God's plan for humankind.

    The Christian epos - Creation, Incarnation and Day of Judgment - owed nothing to pagan historiography, but Christian historians, from Eusebius (d. 340) and Orosius (d. 417) onwards, felt compelled to fit bits and pieces of the pagan record into their histories of how God had dealt with humankind. Innumerable medieval chronicles, therefore, begin with Creation and hurry through familiar landmarks of the Biblical and pagan past in order to attach local and recent events - at least perfunctorily - to the central, sacred meaning of human experience on earth. History, detached from God's purposes, was blind, pointless, misleading; and for something like a thousand years, Christians refused to consider such folly, even though their most painstaking recording of recent events left God's purposes stubbornly inscrutable.

    In China, no such transformation of prevailing views ever took place. Instead, Ssuma Ch'ien's vision of how to write and understand history prevailed from his own time until the collapse of the Manchu dynasty at the beginning of the twentieth century. The central idea was that Heaven chose virtuous hereditary rulers; and allowed (or contrived) their overthrow whenever a ruling dynasty became corrupt. Each new dynasty began virtuous and strong only to decay, sooner or later, provoking the transfer of Heaven's mandate to a new ruler, whose virtue was attested by his practical success in reducing China and surrounding barbarians to obedience. The power of Ssuma Ch'ien's vision is attested by the fact that his dynastic frame for Chinese history still dominates scholarship, even among westerners, who have never believed that the ruler's personal virtue assured supernatural support.

    Moslem, Buddhist and Hindu outlooks upon history also took shape during the Middle Ages. In general, these learned traditions paid less attention to history than Christians and Chinese did; but all agreed on the overriding importance of supernatural intervention in human affairs; and by subordinating events of earth to God's will, as Moslems did, or to supernal processes and interventions, as Buddhists and Hindus did, all agreed that world history was the only meaningful kind of history, since supernatural entities governed human affairs along with the rest of universe according to rules of their own.

    Consensus concerning the decisive role of transcendant beings or forces in history was challenged when a discordant, man-centered version of history found voice in Italy soon after 1500. What inspired the new type of history was the palpable convergence of Italian city-state politics with patterns of Greek and Roman antiquity. Study of pagan writers in privileged circles of a few Italian towns revived as this convergence became evident; and by about 1500 such studies had ripened sufficiently to allow Machiavelli (d. 1520) and Guicciardini (d. 1540) to reaffirm the autonomy of human actions by writing local, monographic and entirely secular histories in the Thucydidean mould. They derived their inspiration unabashedly from pagan writers, and settled accounts with the Biblical framework of universal history simply by leaving God out, not mentioning Him as an actor in history at all.

    This was both shocking and unacceptable to most Europeans. Accordingly, a renaissance man like Walter Raleigh (d. 1618) in England, and, almost a century later, the pious and eloquent Bishop Bossuet (d. 1704) in France, reaffirmed the centrality of sacred history and attempted to weave what they knew about the Biblical and pagan past into a more perfect whole. Their works remained incomplete and never approached their own time: partly because both were bogged down by a rapidly increasing fund of knowledge about events of the more recent past, and partly because God's will remained obscure (or at least radically disputable) when called on to explain the tangled record of those same events.

    Meanwhile, a flood of information about the Americas and other formerly unknown parts of the earth assaulted European consciousness. A few gestures towards fitting the newly discovered peoples into the inherited Christian frame of history were indeed made. In particular, how the inhabitants of America descended from the sons of Noah became a subject of debate. But for the most part, European learning reaffirmed (or at least paid lip service to) Christian truths; explored new fields of knowledge, accumulated more and more information about the past, and about far parts of the earth, and dodged the question of how to fit all the new data together. This remained the case until the 18th century when radical efforts to organize empirical knowledge systematically (stimulated partly by Newton's spectacular success in physics and astronomy) began to meet with apparent success in such fields as botany.

    In these same centuries, the Chinese, Moslem and Indian traditions of learning were far more successful in resisting challenge from without, improving upon the Europeans by refusing to pay attention to new and discrepant information. When a few self-styled Enlightened thinkers, located mainly in France, began to abandon the inherited Christian framework of knowledge entirely, guardians of inherited truth in Asia were not impressed. Instead, serious efforts to come to grips with what eventuality became undeniably superior European knowledge and skills were delayed until almost our own time.

    Against this norm, the volatility of European learning in general and of historiography in particular should perhaps excite our wonder. At the least, we ought not to scorn the centuries-long lag time needed to accommodate new and discrepant information. The historical profession persist in the same behaviour today, remaining for the most part content to work (often unconsciously) within a liberal, nineteenth century interpretation of history whose principles, if overtly affirmed, mostly embarrass because no one believes them any longer.

    Vico (d. 1744), Voltaire (d. 1778), Gibbon (d. 1794) and Herder (d. 1803) pioneered the eighteenth century effort to improve upon the inherited Biblical frame of history. Each in his own way desacralized the past, even though both Vico and Herder remained Christians. Like Guicciardini and Machiavelli, they assumed that human will and actions shaped events; unlike their Florentine predecessors they undertook macrohistory, finding largescale patterns in the past, whether cyclical, as Vico and Herder did, or cumulative and, at least sporadically progressive, as Gibbon and Voltaire did. Classical history and philosophy played a central role in shaping their outlooks. Only Voltaire in his Essai surs les Moeurs (1756) paid much attention to non-Europeans; and his praise for China and his respect for Moslems was largely inspired by his distaste for the Christian church. Hence nothing like a global view of the past emerged from eighteenth century efforts to correct the Christian interpretation of history; but the autonomy of human action was vigorously affirmed, with or without an ultimate, increasingly distant, Divine control.

    This compromise between pagan and Christian heritages carried over into the nineteenth century, when the liberal vision of history took shape. This is what still lurks in the background of contemporary American historiography The core idea was simple enough: what mattered in history was the sporadic but ineluctable advance of Freedom. This allowed nationalistic historians to erect a magnificently Eurocentric vision of the human past, since Freedom (defined largely in terms of political institutions) was uniquely at home among the states of Europe, both in ancient and in modern times. The rest of the world, accordingly, joined the mainstream of history when discovered, settled or conquered by Europeans. A somewhat spurious global history was easy to construct along these lines. Still, for the first time America, Australia, Africa and Asia found an admittedly subordinate but still significant place in world history, and the entire globe became a theatre for the advance of human Freedom.

    Within the European past, attention focused on times and places where Freedom flourished or faced critical challenge. Classical antiquity, the barbarian invasions, the rise of representative institutions in the Middle Ages, Renaissance and Reformation, the Enlightenment and all the magnificent advances of the nineteenth century were what deserved to be studied; eras of darkness and despotism could properly be skipped over since they made no contribution to the main stream of human achievement.

    The United States, of course, enjoyed a specially privileged place in this version of history, since the Revolution of 1776 and the Constitution of 1789 were beacons of Freedom's advance; and the expansion of American wealth and power in the nineteenth and twentieth centuries offered an equally obvious example of the rewards Freedom could bring to its faithful and favored practitioners. This, as I say, is still the scheme that underlies most professional study of history in the United States, even though some rebels have turned everything inside out by making the wickedness of European aggression against other peoples the main theme of modern history, while attacking the white male establishment of the United States for its no less wicked exploitation of various subordinated populations, both at home and abroad.

    Obviously enough, this liberal, progressive view of world history (as well as the inside-out inversion thereof) was a naive secularization of the Christian epos. Freedom replaced God as the governing, supernal actor; and privileged free peoples played the terrestrial role assigned to faithful Christians in the divine drama of salvation. Insofar as the professional pursuit of history finds its meaning in this schemes (or in its inversion) we clearly remain bounded by the Christian inheritance, however faint it has become in contemporary consciousness.

    World War I was hard to accommodate within what has been called the liberal view of history. Freedom to live and die in the trenches was not what nineteenth century historians expected liberal political institutions to result in. Moreover, the agonizing years of stalemate seemed to many participants to arise from circumstances entirely independent of human will or intention. Spengler and Toynbee were the two most significant historians who responded to this apparent loss of control, and to the strange disembowelment that Freedom suffered in World War I. The sense of being caught up in processes overriding to human purposes, and of reenacting in 1914-1918 struggles for power like those that had wracked ancient Greece and Rome, persuaded first Spengler and then Toynbee that human history could best be understood as a more or less foreordained rise and fall of separate civilizations, each recapitulating in essentials the career of its predecessors and contemporaries. Quite consciously, they both drew on their classical education to reaffirm a cyclic vision of human affairs proposed by Plato and elaborated by other philophers of antiquity down to the Stoics, and applied to history by such diverse writers as Polybius and Virgil.

    Their impressively learned books won wide attention between 1918 when the first volume of Spengler's Der Untergang des Abendlandes was published, and 1936-54, when Toynbee's ten volume A Study of History came out in three separate installments. To many thoughtful persons, their books gave a new and somber meaning to such unexpected and distressing events as World War I, Germany's collapse in 1918, the onset of World War II, and the breakup of the victorious Grand Alliances after both wars.

    Today, when these political resonances have faded, a quite different aspect of their work seems more important, since, by cycling through the recorded past, Spengler and Toynbee put European and non-European civilizations on the same plane. This was a real change from the myopic concentration on the glories of Europe's past that had prevailed in the nineteenth century; and, at least potentially, distinguishes the historiography of our age from its predecessors.

    To be sure, Toynbee was not long satisfied with his initial scheme, and in the later volumes of A Study of History (published in l939 and l954) explicitly reintroduced God as an actor in history, subordinating the rise and fall of separate civilizations to a progressive revelation of God's will that came to sensitive souls in times when the moral rules of a given civilization were undergoing irremediable breakdown. This way of combining linear and cyclical macrohistory and of introducing God once more into public affairs won few adherents among historians; and after 1957 his reputation suddenly collapsed, as Spengler's had before him.

    One empirical (and probably trivial) reason for this swing of public and professional attention was that the separate civilizations that Spengler and Toynbee had declared to be unable to communicate with one another, (save for Toynbee at special sensitive moments in their development), did in fact interact with one another whenever contacts occurred. Adaptation to borrowings across civilizational boundaries was especially important in technological, artistic and military matters, where the charms of novelty and the rewards of innovation were particularly obvious. By contrast, literary learning resisted intrusion from afar, partly because mastering an alien language in which interesting ideas might be set forth was always difficult; but also because to admit that outsiders had something to say that was worth attending to seemed a confession of inadequacy that faithful transmitters of a revered literary canon were not prepared to make. Nonetheless, defenders of literary and religous truth sometimes borrowed ideas from outsiders, with or without acknowledeging alien inspiration.

    Cultural and technological borrowings were often incidental to economic exchanges, which have the advantage for historians of leaving material traces behind even when literary records are missing. Long distance trade existed even before the beginning of recorded history, when the river valley civilizations of Mesopotamia and Egypt began to import strategic goods like metal and timber across quite considerable distances from barbarian lands. Inter-civilizational trade, too, was very old. Mesopotamian commercial contacts with India dated back to the third millennium B.C. or before. Indirect and far more tenuous contacts between Mesopotamia and China started a few hundred years later, though caravans only began to move more or less regularly across the oases of central Asia about 100 B.C. Nevertheless, with the passage of time, the scale and range of trade exchanges within Eurasia expanded into Africa and then, after 1500, began to embrace all the inhabited earth.

    Historians have, a bit hesitantly, begun to react to the increasing evidence of long distance interactions that cross the boundaries of traditional scholarly specialization; and a number of persons have set out to construct a more adequate world history than Spengler and Toynbee envisaged by highlighting Eurasian and subsequent global interactions. No one writer stands preeminent in this company, which is divided between those who put primary emphasis on economics - often Marxists or quasi-Marxists like Immanuel Wallerstein and Andre Gunder Frank - and others who think that religious, artistic, and scientific encounters played an autonomous and more or less equal part with economics and technology in defining the course of Eurasian and then of world history. One can also point to such figures as Ross Dunn, the first President of the World History Association, and the company of scholars associated with the International Society for Comparative Study of Civilizations, among whom John Hord and David Wilkinson are among the most vigorous. The very existence of these two organizations, each with its own learned journal, attests to the liveliness that world history has attained in American academic circles; and, as a sign of their vigor, both journals are presently fumbling around in search of a more adequate conceptualization of human history as a whole.

    To be sure, terminological confusion is as dense as ever. Yet even though there is no perceptible consensus about what the term 'civilization' ought to mean, and no agreed word or phrase to describe the 'interactive zone' (to use a coined term) embracing different Eurasian civilizations, it would be correct to assert that recognition of the reality and historical importance of trans-civilizational encounters is on the increase and promises to become the mainstream of future work in world history. We badly need a word or phrase to describe the human reality arising from encounters with strangers who bring locally unfamiliar skills and knowledge to the attention of stay-at-homes. Ross Dunn's interactive zone seems clumsy. A favourite would be ecumene, which however carries cramping ecclesiastical associations. Wallerstein's world system is perhaps the leading candidate at present; but it is awkward as a description of such relationships before 1500, when separate world systems existed in Eurasia, America and presumably elsewhere as well, although we know very little about historical change initiated by the non-literate peoples' interactions, and can only hope that sophisticated archaeology may someday make some of the facts accessible.

    Still, even though we have yet to agree upon what to call it, the fact that civilized and uncivilized peoples communicated across relatively long distances from very early times, and altered their behavior from time to time in response to encounters with attractive or threatening novelties from afar seems more and more obvious. It follows that world history ought to be constructed around this reality -the largest and most inclusive framework of human experience, and the lineal ancestor of the One World in which we find ourselves so confusingly immersed today.

    Let's now sketch the landmarks in the history of the interactive, ecumenical world system of Eurasia, hoping that even a thumb nail sketch may clarify the concept, and promote the emergence of more coherent, intelligible approach to world history.

    Past ideas about the importance of cultural borrowing were largely shaped by social anthropology, as developed in the United States in the 1930s. Clark Wissler had studied the diffusion of 'culture traits' among the Plains Indians with elegant precision; and Ralph Linton's textbook, The Tree of Culture, adduced other persuasive examples of far-reaching social change in Africa and elsewhere as a result of cultural adaptation to some borrowed skill. But a man of great influence was Robert Redfield: he constructed a typology of human societies, setting up two ideal types: folk society at one extreme, civilized society at the other.

    Folk society was one in which well established customs met all ordinary circumstances of life, and fitted smoothly together to create an almost complete and unquestioned guide to life. Redfield argued that a remote Yucatan village he had studied approached his ideal type of folk society. Nearly isolated from outside encounters, the people of the village had reconciled their Spanish Christian and Mayan heritages, blending what had once been conflicting ways of life into a more or less seamless whole. Conflict and change were reprehensible, checked by the sacralizing power of binding custom.

    Civilized society, exemplified by Yucatan's port city of Merida, was at the opposite pole. There Catholicism clashed with residual pagan rites; and continual contacts among strangers meant that customary ruies binding everyone to a consistent body of behaviour could not arise. Instead, conflicting moral claims provoked variable, upredictable conduct. Social conflict and change was obvious and pervasive, feared by some and welcomed by others.

    Armed with ideas like these, it seems somehow obvious that historical change would be largely provoked by encounters with strangers, followed by efforts to borrow (or sometimes to reject or hold at bay) specially attractive novelties. This, in turn, always involves adjustments in other established routines. A would-be world historian therefore ought to be alert to evidences of contacts among separate civilizations, expecting major departures to arise from such encounters whenever some borrowing from (or rejection of) outsiders' practices provoked historically significant social change.

    The ultimate spring of human variability, of course, lies in our capacity to invent new ideas, practices and institutions. But invention also flourished best when contacts with strangers compelled different ways of thinking and doing to compete for attention, so that choice became conscious, and deliberate tinkering with older practices became easy, and indeed often inevitable. In folk society, when custom worked as expected, obstacles to most sorts of social change were all but insuperable. But when clash of customs created confusion, invention flourished. Civilization, as Redfield defined it, was therefore auto-catalytic. Once clashing cultural expections arose at a few cross-roads locations, civilized societies were liable to keep on changing, acquiring new skills, expanding their wealth and power and disturbing other peoples round about. They did so down to our own day, and at an ever increasing pace as the centuries and millennia of civilized history passed.

    Approaching the conceptualization of world history in this fashion, separate civilizations became the main actors in world history - accepting or rejecting new ways come from afar; but in either case, altering older social practices, since successfully to reject an attractive or threatening novelty might require changes at home quite as far reaching as trying to appropriate it. Over time, civilizations clearly tended to expand onto new ground; and as they expanded, autonomous neighboring societies were engulfed and eventually disappeared. Such geographical expansion meant that in the ancient Near East what had begun as separate civilizations in Mesopotamia and Egypt eventually merged into a new cosmopolitan whole, beginning about 1500 B.C.; and an analogous cosmopolitanism began to embrace all the civilizations of the earth after about 1850, when the effective autonomy of China and Japan came to an end.

    But one should note these instances without diverting the focus of attention from the separate histories of separate civilizations. The idea of a Eurasian (eventually also African and then global) ecumenical whole, embracing all the peoples, civilized and uncivilized, who were interacting with one another, dawned very slowly. Only after convincing oneself that Chinese commercial expansion energized the sudden upthrust of trade in Latin Christendom after about 1000 A.D., does one realize, with Wallerstein and Dunn, that a proper world history ought to focus primarily upon changes in the ecumencial world system, and then proceed to fit developments within separate civilizations, and within smaller entities, like states and nations, into the pattern of that fluctuating whole.

    One may define civilization as a style of life, to be recognized by skilled and experienced observers in the way an art critic discerns styles of art. But that analogy is not really a good one. Works of art are tangible; whereas 'life' is too multifarious to be observed in the way art critics can observe and more or less agree about stylistic affinities. In particular, within any civilization, different groups lived in very different ways. What principally held them together was their common subjection to rulers, whose continued dominion was much assisted by the fact that they subscribing to a set of moral rules, embodied in sacred or at least semi-sacred texts. This is the proper definition of a 'civilization.' Rulers who knew how to behave -- paying lip service to prescribed canons of conduct and acting with a more or less exactly agreed upon disregard of the letter of those rules -- could and did cooperate smoothly enough to keep a lid on turbulent subordinates for centuries on end across scores, then hundreds and, eventually, thousands of miles. Privileged ruling classes thus constituted a sort of iron framework within which a civilization could thrive. But among subordinated groups widely diverse local, occupational, and sectarian ways of life prevailed. All that united them was the fact that each group had some sort of tacit (or, occasionally, explicit) understanding with other groups, and especially with the politically dominant segments of society, so that they could act as they did without suffering too many nasty surprises.

    In such a view, civilizations become rather pale, inchoate entities in themselves. Internal diversity looms large and merges almost imperceptibly into the diversity of neighboring peoples who retained varying degrees of local autonomy but still entered into negotiations with civilized rulers and traders, and, mayhap, with missionaries, craftsmen, refugees and, sometimes with colonizing settlers as well. No single recognizable style of life can be imputed to such a social landscape. Diversity, conflict and imprecise boundaries, yes; coherence and uniformity, no.

    Even the canon of sacred writings, to which dominant segments of civilized society subscribed, was full of discrepancies. Consider the Bible, Buddhist and Hindu sacred writings, and the Confucian classics! It required judicious commentary to educe a practicable guide to life from such diverse materials; and, of course, initial diversity implied perennial flexibility, inviting commentators to adjust to ever-altering circumstances by appropriate reinterpretation, age after age, while claiming, characteristically, to be restoring the true, original meaning to the sacred texts. This was the primary function of the literate (often priestly) classes; and explains why new, discrepant, data was (and still is in many branches of learning) so persistently disregarded.

    If civilizations were as internally confused and contradictory, it puts them very much in tune with the confusion and complexity of the Eurasian ecumenical world system. That system was larger in geographic area, of course, and more attenuated in its internal structure, being without any articulated overriding canon of conduct because it embraced a plurality of civilizations (and interstitial peoples), each with its own literary definition of moral principles and its own political and cultural rulers. But, for all that, the ecumene was not so very different from the diversity to be found within the borders of any of the larger civilizations that by 1500 were participating in the Eurasian and African circle of exchange and interaction.

    The reason was that mercantile practice had, in fact, slowly created a workable code of conduct that went a long way towards standardizing encounters across cultural boundaries. Even the arcanum of religion made room for outsiders and unbelievers, since the principal religions of the Eurasian world - Christianity, Confucianism, Buddhism and Islam - all agreed in exhorting the devout to treat strangers as they would wish to be treated themselves. Thus, despite the fact that no single set of rulers had ever exercised political sovereignty across the whole Eurasian-African ecumene, a bare-bones moral code did arise that went a long way towards reducing the risks of cross-civilizational contact to bearable proportions. Little by little across the centuries, local rulers of every stripe learnt that they could benefit mightily by taxing instead of plundering strangers. Subordinate classes also learned to tolerate outsiders - even alien merchants, whom hardworking peasants and artisans regularly regarded as dishonest exploiters who reaped profit unjustly, since what they sold dear was exactly the same as what they had previously bought cheap from honest men, i.e., from themselves. All the same, the poor gradually got used to being cheated by outsiders in the marketplace, just as their forerunners at the dawn of civilization had gotten used to surrendering unrequited rent to self-appointed, strong armed landowners.

    As these attitudes became general, so that an enforcible (and remarkably uniform) law merchant arose in the ports and other great urban centers of Eurasia, and was supplemented by an informal body of customs for dealing with strangers that extended into the rural hinterland, the structure of the ecumenical world system approximated very closely to that of the separate civilizations embraced within it.

    Antique World Map


    What, then, were the major landmarks in the historical evolution of this, the largest and, eventually, world-dominating framework of human experience?

    As one would expect, if one is right in claiming that encounters with strangers were the main drive wheel of social change, the earliest complex societies arose on the river flood plains of Mesopotamia, Egypt and northwest India, adjacent to the land bridge of the Old World, where the largest land masses of the earth connect with one another. Continental alignments and climatic conditions made this region the principal node of land and sea communications within the Old World, and it was presumably for that reason that civilization first broke out there.

    Sumerian literary tradition accords with this notion, since it held that the founders of their civilization had come by sea from the south and subdued the 'black headed people' who were indigenous to the banks of the lower Tigris - Euphrates. The newcomers eventually learned to irrigate the swamp lands that bordered the rivers, and thanks to regular and assured harvests were then able to erect earth's first cities on an alluvial plain that lacked timber, metals and other essential raw materials the Sumerians needed. From their inception, therefore, shipping, supplemented by overland caravans, kept the cities of the Mesopotamian plain in touch (directly or indirectly) with distant sources of raw materials and diverse peoples living within a radius of several hundred miles. And, before long, inhabitants of Egypt and of the Indus valley erected civilizations of their owns thanks partly to borrowed skills and ideas acquired through contact with Mesopotamia, and by doing so promptly established their own zones of interaction with peoples round about, just as the Sumerians had done before them.

    Initially, water transport was the main link across long distances. When, at an early but unknown date, human beings discovered the use of sails, the coastal waters of the Indian ocean and its adjacent seas became an especially easy medium of transport and communication. Winds blew equably throughout the year, and their direction reversed itself with each monsoon. This made safe return from lengthy voyages exceptionally easy, even for ships that could not sail against the wind. If Sumerian tradition is to be believed, the founders of the world's first civilization emerged from this sea-room, bringing with them superior skills that had been accumulated, we may surmise, before the dawn of recorded history thanks to contacts with strangers provoked by sea travel.

    About 4000 B.C. sailing ships also began to ply the Mediterranean, where comparably benign (though not quite so convenient) sailing conditions prevailed in summer time when the trade winds blew gently and steadily from the north east. Safe return to home base often required going against the prevailing wind. Rowing was one possibility, and remained important in Mediterranean navigation until the seventeenth century A.D. Taking advantage of short-lived off-shore winds created by differential heating or sea and land was another possibility. Ship and sail design that permitted tacking into the wind was a more satisfactory solution, but was not fully attained until the late middle ages. Yet ships that moved up-wind with difficulty, and could not sail the stormy seas of winter safely, were quite enough to provoke and sustain the emergence of Minoan, Phoenician Carthaginian and Greco-Roman civilizations. Borrowings from Egypt and Syria were critical at the start - and most such contacts were by sea.

    Geographically speaking, the south China sea was about as hospitable to early sailing ships as the Mediterranean. But the possibility of seasonal navigation in south east Asia and among adjacent off-shore islands did not lead to the early development of cities and literate civilizations, perhaps because no developed civilized centers were at hand from which to borrow critical skills and ideas. Similarly, the most congenial sea spaces of all the earth were the vast trade wind zones of the Atlantic and Pacific oceans; but they too were not exploited until large ships that could tack against the wind had been invented, though Polynesian canoes did carry human settlers to remote islands of the Pacific throughout the trade wind zone. The North Atlantic and North Pacific were far more formidable for early sailors since stormys variable winds were further complicated by the high tides.

    Thus climate and wind patterns set definite limits to early shipping, though it is worth noting that small coracles, made of wickerwork and hides, did begin to fish the coastal waters of the North Atlantic in the third millennium B.C. Fishermen also embarked from the shores of Japan from an unknown but presumably early date. Accidental drift voyages across the breadth of the oceans must have set in as soon as fishing boats started to venture onto these stormy waters. Drift voyages of Eskimo kayaks from Greenland that fetched up in Scotland in the seventeenth century, and Japanese fishermen who came ashore in Oregon in the nineteenth century offer a well attested sample of the random, ocean-crossing dispersals suffered by small craft lost at sea.

    A few resemblances between Amerindian artifacts and those of east Asia may result from drift voyages; but fishermen did not carry much cultural baggage with them, even when they survived weeks of exposure; and it is unlikely that the real but trivial trans-oceanic contacts (including Norse settlements in North America) had enduring consequences of any importance before 1492. Instead, a separate ecumenical system arose in the Americas, centered in Mexico and Peru; but in the absence of an extended literary record we know far less abut its development and, since archaeology is inherently local, connections among separate sites frequently remain obscure.

    Eurasian ecumenical history is far more accessible, even though historians have not yet studied its growth and consolidation in detail. Nonetheless, it is clear enough that the initial primacy of sea transport and communication in holding the ecumene together was gradually modified by improvements in transport overland. Human beings, of course, were rovers from the start: that is how they populated the earth. With the development of agriculture, the diffusion of useful crops set in. Slash and burn cultivators, for example, carried wheat from the Near East to China, where it arrived before 2OOO B.C. Rice spread from somewhere in south east Asia and became an important crop in both India and China about a thousand years later. Other, less important crops spread as well, altering human life profoundly wherever they began to provide a new source of food for the population.

    Before the dawn of literacy, human portage and wandering had been supplemented, at least in some parts of the world, by caravans of pack animals, which made carrying goods much easier. Long distance exchange became routine in Sumerian times, when donkey caravans brought metals and other precious commodities from as far away as the Carpathian mountains of Romania and distributed textiles and other manufactured goods in return. Caravan trade thus came to resemble trade by sea, with the difference that carrying valuable goods through inhabited lands required the negotiation of protection rents with every local ruler, whereas ships usually only had to pay tolls at their ports of destination. Since risk of plunder by some local ruffian was far higher than the risk of piracy at sea, costs of caravan transport remained comparatively high, so that only precious goods could bear the cost of long distance land transport.

    Overland contacts took a decisive new turn after about 1700 B.C. when light, manoeuverable chariots were invented somewhere in the Mesopotamian borderlands. A team of horses hitched to such a vehicle could carry driver and bowman across open country faster than a man could run; and, when new, an array of charging chariots proved capable of overwhelming opposing infantry with ease. As a result, charioteers overran the river valley civilizations of the Near East and India before and after 1500 B.C. Others penetrated Europe and China, where the earliest archaeologically well-attested Chinese dynasty, the Shang, established itself about 1400 B.C. with the help of war chariots. As the spread of wheat (and of some pottery styles from western Asia) shows, swift wheeled transport and the military superiority of charioteers that resulted did not initiate trans-Asian encounters; but the establishment of the Shang dynasty through the exploitation of military techniques that originated in the Mesopotamian borderiands apparently did inaugurate many of the historical forms or Chinese civilization. This is strikingly attested by inscriptions on oracle bones discovered at the Shang capital of Anyang which are directly ancestral to the characters of contemporary Chinese writing.

    Communication between China and western Asia remained sporadic and indirect for many centuries after 1400 B.C. Even when Chinese imperial initiative inaugurated more or less regular caravan trade after 100 B.C., goods that survived the long journey remained mere curiosities and expensive luxuries. A few fashionable Roman ladies did indeed clothe themselves in semi-transparent silks from China; and the Chinese emperor did succed in importing large-boned 'blood sweating' horses from Iran, only to find that the scrawny steppe ponies, with which Chinese soldiers had already come to terms, were so much hardier and cheaper to keep that the imported breed could not displace them for anything but ceremonial purposes.

    Yet the inauguration of more or less regular caravan trade across Asia did connect east and west as never before; and when, after about 300 A.D., camels were brought into general use, caravans became capable of crossing previously inhospitable deserts. The effect was to incorporate vast new areas of Eurasia and Africa into an expanded trade and communications network. Tibet, Arabia and the oases of central Asia, on the one hand, and sub-Saharan West Africa on the other entered firmly into the ecumenical system, which simultaneously expanded northward by penetrating the whole of the steppes from Manchuria to Hungary, and even filtered across mountain passes and along river courses into the forested fastnesses of northern Europe.

    New and highly lethal epidemic diseases and the so-called higher religions were the two most significant novelties that spread through this expanded caravan world from shortly before the Christian era to about 1000 A.D. Material exchanges, like the spread of south east Asian fruits and other crops to the Middle East with the elaboration of oasis agriculture, or the diffusion of Greco-Roman naturalistic sculptural styles to India, China and even Japan were trivial by comparison with the epidemiological and religious changes that this transport system precipitated.

    This balance between economic/technological and cultural/biological exchanges altered after about 1000 A.D. when the ecumenical world system began to respond to innovations within China that expanded the role of market behavior by bringing poor peasants and urban working classes within its scope for the first time. What made this possible was cheap and reliable transport within China, resulting from widespread canal construction. Most canalization was initialty undertaken to regulate water supplies for the expanding carpet of rice paddies upon which China's food more and more depended. Then with the construction of the Grand Canal in 605, linking the watershed of the Yang-tse with the Yellow river system, accompanied and followed by other engineering works designed to facilitate navigation through the Yang-tse gorges and other critical bottlenecks, the most fertile parts of China came to be linked by easily accessible and easily navigable waterways. Under the distant sovereignty of the Emperor, canal boats could carry comparatively bulky cargoes across hundreds of miles with minimal risk of shipwreck or robbery. This, in turn, meant that even small differences in price for commodities of common consumption made it worth while for boatmen to carry such goods from where they were cheap to where they were dear.

    Then, when, soon after 1000, the Sung government found it more convenient to collect taxes in cash instead of in kind, as had always been done previously, common people, including the poorest peasants, were forced onto the market so as to be able to pay their taxes. This enormously accellerated the spread of market behaviour throughout China. Thereupon, to the general surprise of officialdom, whose Confucian training classified traders as deplorable social parasites, the advantages of specialized production, which Adam Smith was later to analyze so persuasively, started to come on stream throughout the varied landscapes of China. Wealth and productivity shot upwards. New skills developed making China the wonder of the rest of the world, as Marco Polo and other visitors from afar soon realized. Among the new Chinese skills, some proved revolutionary: most notably, for Europe, the trinity of gunpowder, printing and the compass, all of which reached Europe from China between the thirteenth and fifteenth centuries.

    China's westward reach was enhanced by the development of ocean-going all-weather ships, capable of tacking against the wind and of surviving most storms. Such ships, based mainly along the south China coast, where inland canal construction was checked by the mountainous interior, allowed enterprising merchants to extend a new (or perhaps only intensified and expanded) trade network across the south China sea and into the Indian ocean. There stoutly-built Chinese vessels had to compete with the light craft and experienced mercantile population indigeneous to those waters. As happened subsequently, when European ships penetrated the Indian ocean by circumnavigating Africa, local shipping and trading networks proved capable of undercutting the higher costs borne by large, all-weather, stout-built intruders. But all the same, a comparatively massive infusion of Chinese commodites and Chinese demand for spices and other Indian ocean products gave a fillip to the markets of the southern seas that soon slopped over into the Mediterranean and helped to stimulate the remarkable revival of European trade in the eleventh century and subsequently, with which historians have long been familiar.

    Traders' needs, in turn, provoked Europeans to develop all-weather ships that were capable of traversing the stormy, tide-beset seas of the North Atlantic and have a reasonable chance of getting back to home ports safely. Inventions introduced between about 1000 and 1400 such as double planking nailed to a heavy keel-and-rib frame, powerful stern post rudders, decked-over holds, and multiple masts and sails made this possible. European ship building followed a course of its own, independent of Chinese or any other foreign model, even though European sailors were always ready to borrow anything that worked in practice, like compass navigation coming from China and triangular sails coming from the Indian ocean.

    Their most fateful borrowing and adaptation, however, was the marriage European seamen made between stout-built, ocean-going ships and cannon, developed initially to knock down castle walls on land. Such big guns, once adapted for use on shipboard, provided European ships with an armament far superior to anything previously known. As a result, when European ships began to sail across all the oceans of the earth, just before and after 1500, they were remarkably safe against attack by sea; and could often overwhelm local reisistance on shore with wall-destroying broadsides.

    The recoil from such guns was so powerful that only heavy ships could sustain it without shaking apart. The Chinese might have matched European ships in this respect, but for reasons domestic to imperial politics, the Chinese government prohibited the construction of ocean-going ships after 1434, and made private Chinese oceanic enterprise illegal. Operating as pirates systematically handicapped Chinese (and Japanese) sailors thereafter and deprived them of any chance or arming their vessels with heavy guns like those European traders carried routinely.

    The consequences of European oceanic discoveries are well known, as are the consequences of the extraordinary improvements of transport and communication that came after 1850, when European, American and more recently also Japanese inventors utilized mechanical and electrical forms of energy for railroads steamships, telegraph and then for airplanes, radio, TV and, most recently, for the transmission of computer data as well. The most obvious effect of these successive transformations of world communications was to expand the reach of the Eurasian ecumene throughout the globe, engulfing the previously independent ecumenical system of America, together with less well-known social complexes in Australia and in innumerable smaller islands. The shock was enormous, and the world is still reverberating to the ecological, epidemiological, demographic, cultural and intellectual consequences of the global unification of the past five hundred years.

    Among other things, global communication and transport made world history a palpable reality. Historians, being the faithful guardians of every level of human collective identity, are beginning to adapt to that circumstance, almost half a millennium after it began to affect human life everywhere. The historical profession still clings to more local (and more sacred) forms of history, and has not yet agreed upon how to approach the human adventure on earth as a whole.

    In struggling with this question, it seems appropriate to emphasize two distinct levels of human encounters that took place across the centuries within the communications networks I have just sketched for you. First is biological and ecological: how human beings fared in competition with other forms of life, managing to not only to survive but to expand their share of the earth's matter and energy, age after age, and in a great variety of different physical environments. No other species comes near to equalling humanity's dominating role in earth's ecosystem. Major landmarks are obvious enough, starting with initial diffusion of hunters and gatherers from Africa, followed by intensified broad-spectrum gathering leading to agriculture; and then the rise of civilizations with enhanced formidability vis-a-vis other societies due to their military specialists on the one hand and their adaptation to crowd diseases on the other. The growing importance of the Eurasian ecumenical world system then takes over, diffusing diseases, crops, technological skill across larger and larger areas, until after 1500 the process became global. Each time a previously isolated population entered into contact with the ecumenical world system debilitating exposure to unfamiliar diseases, ideas and techniques ensued; often with disastrous results for the previously isolated peoples and their cultures.

    Uniformity never emerged, and there is no reason to suppose it ever will. Differences of climate and other circumstances require different behaviour, and being both intelligent and adaptible, human beings act accordingly. Some forms of life have been destroyed by the human career on earth; many more are endangered, as we all know. Others have been carried into new environments and made to flourish as never before. Some disease organisms and weed species still defy human wishes successfully; but domesticated plants and animals have been radically altered and some entirely new species of plants and animals have been invented to nourish us and serve our wants (and wishes) in other ways.

    What makes the human career on the face of the earth so extraordinary from a biological/ecological point of view is that in becoming fully human our predecessors introduced cultural evolution, as soon as learned behaviour began to govern most of their activity. The consequent cultural attainments of humankind, and their variability in time and space, thus constitute the second level of world history. Attention has traditionally and quite properly centered here because what has been learned can change whenever something new and attractive comes to conscious attention. And since consciousness is extremely motile, cultural evolution immediately outstripped organic evolution, introducing a radically new sort of disturbance into earth's ecosystem.

    Yet in some respects cultural evolution still conforms to the older patterns of organic evolution. Initial, more or less random variation and subsequent selection of what works best is enough to set the process in motion. Contacts among bearers of different cultural traditions promoted further change; but as already argued, changes were often initiated to defend local peculiarities rather than to accept what was perceived as an alien, and often threatening, novelty. It follows that even the instantaneous communication that prevails today is unlikely to result in any sort of global uniformity. Human groups, even while borrowing from outsiders, cherish a keen sense of their uniqueness. The more they share, the more each group focuses attention on residual differences, since only so can the cohesion and morale of the community sustain itself.

    The upshot has always been conflict, rivalry and chronic collision among human groups, both great and small. Even if world government were to come, such rivalries would not cease, though their expression would have to alter in deference to the overriding power or a bureaucratic world administration. In all probability, human genetic inheritance is attuned to membership in a small, primary community. Only so can life have meaning and purpose. Only so can moral rules be firm and definite enough to simplify choices. But membership in such groups perpetuates the gap between us and them and invites conflict since the best way to consolidate any group is to have an enemy close at hand.

    Until very recently, rural villages constituted the primary communities that shaped and gave direction to most human lives. But with modern communications and the persistent spread of market relations into the countryside, this has begun to change. Multiple and often competing identities, characteristic of cities from ancient times, have begun to open before the astonished and often resentful eyes of the human majority. How to choose between the alternative collective identities, and how to reconcile conflicting obligations that different identities impose is the perennial moral problem of all human society. In the past, most rural communities worked out more or less unambiguous rules for making such choices, so that moral behavior was usually obvious to all concerned. In urban contexts, friction and uncertainty were far greater; and today, as urbanity expands into the countryside, ambiguity and uncertainty multiply everywhere.

    How to reconcile membership in vivacious primary communities with the imperatives of an emerging cosmopolitanism is, perhaps, the most urgent issue of our time. The material advantages of global exchange and economic specialization are enormous. Without such a system, existing human populations could scarcely survive, much less sustain existing standards of living. But how firm adhesion to primary communities can be reconciled with participation in global economic and political processes is yet to be discovered. Religious congregations of fellow believers emerged in antiquity in response to analogous needs; and possibly something similar may happen again. But contemporary communications expose the faithful to a continual bombardment by messages from outsiders and unbelievers. Moreover, if that could somehow be successfully counteracted, rival religious communities then might clash, with results as disastrous as those arising from the twentieth century's clash of rival nations.

    Human affairs are trembling on the verge of far-reaching transformation, analogous to what happened when agriculture emerged out of broad-spectrum gathering, and village communities became the principal framework within which human lives were led. What sort of communities may prove successful in accommodating their members to global communications, world wide exchanges and all the other conditions of contemporary (and future) human life remains to be seen. Catastrophe of unprecedented proportions is always possible. We are all aware of potential ecological disasters, due to pollution of land, air and water. Social breakdown due to deficient or misguided nurture is perhaps no less threatening.

    But human ingenuity and inventiveness remains as lively as ever; and perhaps satisfying and sustainable inventions will indeed occur locally and then spread, as other inventions in times past, having proved themselves in practice, also spread through imitation and adaptation, thus adding to the sum of human skills and enlarging the scope of human life, age after age, through emergency after emergency and crisis after crisis, from the beginning of the human career on earth to our time. Risks may be greater than ever before, but possibilities are correspondingly vast.

    We live, whether we like it or not, in a golden age when precedents for the future are being laid down. It seems apparent that by constructing a perspicacious and accurate world history, historians can play a modest but useful part in facilitating a tolerable future for humanity as a whole and for all its different parts. The changing shape of world history is a worthy and fascinating study, apt for our age, and practically useful inasmuch as a clear and vivid sense of the whole human past can help to soften future conflicts by making clear what we all share.


    Mayan temple


    • ~ Main e-reference: Wikipedia (thank you, Wiki!)


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