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Guns, Germs, and Steel

The Fates of Human Societies

by Jared Diamond

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Jared Diamond dismantles racially based theories of human history by revealing the environmental factors he feels are responsible for history's broadest patterns.

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Excerpt: Guns, Germs, And Steel

Guns, Germs, and Steel

The Fates of Human Societies

W. W. Norton & Company

Copyright © 1999 Jared Diamond
All right reserved.

ISBN: 0393317552

Chapter One


    A suitable starting point from which to compare historical developmentson the different continents is around 11,000 B.C.(*) This date correspondsapproximately to the beginnings of village life in a few parts of the world,the first undisputed peopling of the Americas, the end of the PleistoceneEra and last Ice Age, and the start of what geologists term the RecentEra. Plant and animal domestication began in at least one part of the worldwithin a few thousand years of that date. As of then, did the people ofsome continents already have a head start or a clear advantage over peoplesof other continents?

    If so, perhaps that head start, amplified over the last 13,000 years, providesthe answer to Yali's question. Hence this chapter will offer a whirlwindtour of human history on all the continents, for millions of years, fromour origins as a species until 13,000 years ago. All that will now be summarizedin less than 20 pages. Naturally, I shall gloss over details and mentiononly what seem to me the trends most relevant to this book.

    Our closest living relatives are three surviving species of great ape:the gorilla, the common chimpanzee, and the pygmy chimpanzee (also knownas bonobo). Their confinement to Africa, along with abundant fossil evidence,indicates that the earliest stages of human evolution were also playedout in Africa. Human history, as something separate from the history ofanimals, began there about 7 million years ago (estimates range from 5to 9 million years ago). Around that time, a population of African apesbroke up into several populations, of which one proceeded to evolve intomodern gorillas, a second into the two modern chimps, and the third intohumans. The gorilla line apparently split off slightly before the splitbetween the chimp and the human lines.

    Fossils indicate that the evolutionary line leading to us had achieveda substantially upright posture by around 4 million years ago, then beganto increase in body size and in relative brain size around 2.5 millionyears ago. Those protohumans are generally known as Australopithecus africanus,Homo habilis, and Homo erectus, which apparently evolved into each otherin that sequence. Although Homo erectus, the stage reached around 1.7 millionyears ago, was close to us modern humans in body size, its brain size wasstill barely half of ours. Stone tools became common around 2.5 millionyears ago, but they were merely the crudest of flaked or battered stones.In zoological significance and distinctiveness, Homo erectus was more thanan ape, but still much less than a modern human.

    All of that human history, for the first 5 or 6 million years after ourorigins about 7 million years ago, remained confined to Africa. The firsthuman ancestor to spread beyond Africa was Homo erectus, as is attestedby fossils discovered on the Southeast Asian island of Java and conventionallyknown as Java man (see Figure 1.1). The oldest Java "man" fossils--ofcourse, they may actually have belonged to a Java woman--have usually beenassumed to date from about a million years ago. However, it has recentlybeen argued that they actually date from 1.8 million years ago. (Strictlyspeaking, the name Homo erectus belongs to these Javan fossils, and theAfrican fossils classified as Homo erectus may warrant a different name.)At present, the earliest unquestioned evidence for humans in Europe stemsfrom around half a million years ago, but there are claims of an earlierpresence. One would certainly assume that the colonization of Asia alsopermitted the simultaneous colonization of Europe, since Eurasia is a singlelandmass not bisected by major barriers.

    That illustrates an issue that will recur throughout this book. Wheneversome scientist claims to have discovered "the earliest X"--whetherX is the earliest human fossil in Europe, the earliest evidence of domesticatedcorn in Mexico, or the earliest anything anywhere--that announcement challengesother scientists to beat the claim by finding something still earlier.In reality, there must be some truly "earliest X," with all claimsof earlier X's being false. However, as we shall see, for virtually anyX, every year brings forth new discoveries and claims of a purported stillearlier X, along with refutations of some or all of previous years' claimsof earlier X. It often takes decades of searching before archaeologistsreach a consensus on such questions.

    By about half a million years ago, human fossils had diverged from olderHomo erectus skeletons in their enlarged, rounder, and less angular skulls.African and European skulls of half a million years ago were sufficientlysimilar to skulls of us moderns that they are classified in our species,Homo sapiens, instead of in Homo erectus. This distinction is necessarilyarbitrary, since Homo erectus evolved into Homo sapiens. However, theseearly Homo sapiens still differed from us in skeletal details, had brainssignificantly smaller than ours, and were grossly different from us intheir artifacts and behavior. Modern stone-tool-making peoples, such asYali's great-grandparents, would have scorned the stone tools of half amillion years ago as very crude. The only other significant addition toour ancestors' cultural repertoire that can be documented with confidencearound that time was the use of fire.

    No art, bone tool, or anything else has come down to us from early Homosapiens except for their skeletal remains, plus those crude stone tools.There were still no humans in Australia, for the obvious reason that itwould have taken boats to get there from Southeast Asia. There were alsono humans anywhere in the Americas, because that would have required theoccupation of the nearest part of the Eurasian continent (Siberia), andpossibly boat-building skills as well. (The present, shallow Bering Strait,separating Siberia from Alaska, alternated between a strait and a broadintercontinental bridge of dry land, as sea level repeatedly rose and fellduring the Ice Ages.) However, boat building and survival in cold Siberiawere both still far beyond the capabilities of early Homo sapiens.

    After half a million years ago, the human populations of Africa and westernEurasia proceeded to diverge from each other and from East Asian populationsin skeletal details. The population of Europe and western Asia between130,000 and 40,000 years ago is represented by especially many skeletons,known as Neanderthals and sometimes classified as a separate species, Homoneanderthalensis. Despite being depicted in innumerable cartoons as apelikebrutes living in caves, Neanderthals had brains slightly larger than ourown. They were also the first humans to leave behind strong evidence ofburying their dead and caring for their sick. Yet their stone tools werestill crude by comparison with modern New Guineans' polished stone axesand were usually not yet made in standardized diverse shapes, each witha clearly recognizable function.

    The few preserved African skeletal fragments contemporary with the Neanderthalsare more similar to our modern skeletons than to Neanderthal skeletons.Even fewer preserved East Asian skeletal fragments are known, but theyappear different again from both Africans and Neanderthals. As for thelifestyle at that time, the best-preserved evidence comes from stone artifactsand prey bones accumulated at southern African sites. Although those Africansof 100,000 years ago had more modern skeletons than did their Neanderthalcontemporaries, they made essentially the same crude stone tools as Neanderthals,still lacking standardized shapes. They had no preserved art. To judgefrom the bone evidence of the animal species on which they preyed, theirhunting skills were unimpressive and mainly directed at easy-to-kill, not-at-all-dangerousanimals. They were not yet in the business of slaughtering buffalo, pigs,and other dangerous prey. They couldn't even catch fish: their sites immediatelyon the seacoast lack fish bones and fishhooks. They and their Neanderthalcontemporaries still rank as less than fully human.

    Human history at last took off around 50,000 years ago, at the time ofwhat I have termed our Great Leap Forward. The earliest definite signsof that leap come from East African sites with standardized stone toolsand the first preserved jewelry (ostrich-shell beads). Similar developmentssoon appear in the Near East and in southeastern Europe, then (some 40,000years ago) in southwestern Europe, where abundant artifacts are associatedwith fully modern skeletons of people termed Cro-Magnons. Thereafter, thegarbage preserved at archaeological sites rapidly becomes more and moreinteresting and leaves no doubt that we are dealing with biologically andbehaviorally modern humans.

    Cro-Magnon garbage heaps yield not only stone tools but also tools of bone,whose suitability for shaping (for instance, into fishhooks) had apparentlygone unrecognized by previous humans. Tools were produced in diverse anddistinctive shapes so modern that their functions as needles, awls, engravingtools, and so on are obvious to us. Instead of only single-piece toolssuch as hand-held scrapers, multipiece tools made their appearance. Recognizablemultipiece weapons at Cro-Magnon sites include harpoons, spear-throwers,and eventually bows and arrows, the precursors of rifles and other multipiecemodern weapons. Those efficient means of killing at a safe distance permittedthe hunting of such dangerous prey as rhinos and elephants, while the inventionof rope for nets, lines, and snares allowed the addition of fish and birdsto our diet. Remains of houses and sewn clothing testify to a greatly improvedability to survive in cold climates, and remains of jewelry and carefullyburied skeletons indicate revolutionary aesthetic and spiritual developments.

    Of the Cro-Magnons' products that have been preserved, the best known aretheir artworks: their magnificent cave paintings, statues, and musicalinstruments, which we still appreciate as art today. Anyone who has experiencedfirsthand the overwhelming power of the life-sized painted bulls and horsesin the Lascaux Cave of southwestern France will understand at once thattheir creators must have been as modern in their minds as they were intheir skeletons.

    Obviously, some momentous change took place in our ancestors' capabilitiesbetween about 100,000 and 50,000 years ago. That Great Leap Forward posestwo major unresolved questions, regarding its triggering cause and itsgeographic location. As for its cause, I argued in my book The Third Chimpanzeefor the perfection of the voice box and hence for the anatomical basisof modern language, on which the exercise of human creativity is so dependent.Others have suggested instead that a change in brain organization aroundthat time, without a change in brain size, made modern language possible.

    As for the site of the Great Leap Forward, did it take place primarilyin one geographic area, in one group of humans, who were thereby enabledto expand and replace the former human populations of other parts of theworld? Or did it occur in parallel in different regions, in each of whichthe human populations living there today would be descendants of the populationsliving there before the leap? The rather modern-looking human skulls fromAfrica around 100,000 years ago have been taken to support the former view,with the leap occurring specifically in Africa. Molecular studies (of so-calledmitochondrial DNA) were initially also interpreted in terms of an Africanorigin of modern humans, though the meaning of those molecular findingsis currently in doubt. On the other hand, skulls of humans living in Chinaand Indonesia hundreds of thousands of years ago are considered by somephysical anthropologists to exhibit features still found in modern Chineseand in Aboriginal Australians, respectively. If true, that finding wouldsuggest parallel evolution and multiregional origins of modern humans,rather than origins in a single Garden of Eden. The issue remains unresolved.

    The evidence for a localized origin of modern humans, followed by theirspread and then their replacement of other types of humans elsewhere, seemsstrongest for Europe. Some 40,000 years ago, into Europe came the Cro-Magnons,with their modern skeletons, superior weapons, and other advanced culturaltraits. Within a few thousand years there were no more Neanderthals, whohad been evolving as the sole occupants of Europe for hundreds of thousandsof years. That sequence strongly suggests that the modern Cro-Magnons somehowused their far superior technology, and their language skills or brains,to infect, kill, or displace the Neanderthals, leaving behind little orno evidence of hybridization between Neanderthals and Cro-Magnons.

    The great leap Forward coincides with the first proven major extensionof human geographic range since our ancestors' colonization of Eurasia.That extension consisted of the occupation of Australia and New Guinea,joined at that time into a single continent. Many radiocarbondated sitesattest to human presence in Australia/New Guinea between 40,000 and 30,000years ago (plus the inevitable somewhat older claims of contested validity).Within a short time of that initial peopling, humans had expanded overthe whole continent and adapted to its diverse habitats, from the tropicalrain forests and high mountains of New Guinea to the dry interior and wetsoutheastern corner of Australia.

    During the Ice Ages, so much of the oceans' water was locked up in glaciersthat worldwide sea levels dropped hundreds of feet below their presentstand. As a result, what are now the shallow seas between Asia and theIndonesian islands of Sumatra, Borneo, Java, and Bali became dry land.(So did other shallow straits, such as the Bering Strait and the EnglishChannel.) The edge of the Southeast Asian mainland then lay 700 miles eastof its present location. Nevertheless, central Indonesian islands betweenBali and Australia remained surrounded and separated by deepwater channels.To reach Australia/New Guinea from the Asian mainland at that time stillrequired crossing a minimum of eight channels, the broadest of which wasat least 50 miles wide. Most of those channels divided islands visiblefrom each other, but Australia itself was always invisible from even thenearest Indonesian islands, Timor and Tanimbar. Thus, the occupation ofAustralia/New Guinea is momentous in that it demanded watercraft and providesby far the earliest evidence of their use in history. Not until about 30,000years later (13,000 years ago) is there strong evidence of watercraft anywhereelse in the world, from the Mediterranean.

    Initially, archaeologists considered the possibility that the colonizationof Australia/New Guinea was achieved accidentally by just a few peopleswept to sea while fishing on a raft near an Indonesian island. In an extremescenario the first settlers are pictured as having consisted of a singlepregnant young woman carrying a male fetus. But believers in the fluke-colonizationtheory have been surprised by recent discoveries that still other islands,lying to the east of New Guinea, were colonized soon after New Guinea itself,by around 35,000 years ago. Those islands were New Britain and New Ireland,in the Bismarck Archipelago, and Buka, in the Solomon Archipelago. Bukalies out of sight of the closest island to the west and could have beenreached only by crossing a water gap of about 100 miles. Thus, early Australiansand New Guineans were probably capable of intentionally traveling overwater to visible islands, and were using watercraft sufficiently oftenthat the colonization of even invisible distant islands was repeatedlyachieved unintentionally.

    The settlement of Australia/New Guinea was perhaps associated with stillanother big first, besides humans' first use of watercraft and first rangeextension since reaching Eurasia: the first mass extermination of largeanimal species by humans. Today, we regard Africa as the continent of bigmammals. Modern Eurasia also has many species of big mammals (though notin the manifest abundance of Africa's Serengeti Plains), such as Asia'srhinos and elephants and tigers, and Europe's moose and bears and (untilclassical times) lions. Australia/New Guinea today has no equally largemammals, in fact no mammal larger than 100-pound kangaroos. But Australia/NewGuinea formerly had its own suite of diverse big mammals, including giantkangaroos, rhinolike marsupials called diprotodonts and reaching the sizeof a cow, and a marsupial "leopard." It also formerly had a 400-poundostrichlike flightless bird, plus some impressively big reptiles, includinga one-ton lizard, a giant python, and land-dwelling crocodiles.

    All of those Australian/New Guinean giants (the so-called megafauna) disappearedafter the arrival of humans. While there has been controversy about theexact timing of their demise, several Australian archaeological sites,with dates extending over tens of thousands of years, and with prodigiouslyabundant deposits of animal bones, have been carefully excavated and foundto contain not a trace of the now extinct giants over the last 35,000 years.Hence the megafauna probably became extinct soon after humans reached Australia.

    The near-simultaneous disappearance of so many large species raises anobvious question: what caused it? An obvious possible answer is that theywere killed off or else eliminated indirectly by the first arriving humans.Recall that Australian/New Guinean animals had evolved for millions ofyears in the absence of human hunters. We know that Galapagos and Antarcticbirds and mammals, which similarly evolved in the absence of humans anddid not see humans until modern times, are still incurably tame today.They would have been exterminated if conservationists had not imposed protectivemeasures quickly. On other recently discovered islands where protectivemeasures did not go into effect quickly, exterminations did indeed result:one such victim, the dodo of Mauritius, has become virtually a symbol forextinction. We also know now that, on every one of the well-studied oceanicislands colonized in the prehistoric era, human colonization led to anextinction spasm whose victims included the moas of New Zealand, the giantlemurs of Madagascar, and the big flightless geese of Hawaii. Just as modernhumans walked up to unafraid dodos and island seals and killed them, prehistorichumans presumably walked up to unafraid moas and giant lemurs and killedthem too.

    Hence one hypothesis for the demise of Australia's and New Guinea's giantsis that they met the same fate around 40,000 years ago. In contrast, mostbig mammals of Africa and Eurasia survived into modern times, because theyhad coevolved with protohumans for hundreds of thousands or millions ofyears. They thereby enjoyed ample time to evolve a fear of humans, as ourancestors' initially poor hunting skills slowly improved. The dodo, moas,and perhaps the giants of Australia/New Guinea had the misfortune suddenlyto be confronted, without any evolutionary preparation, by invading modernhumans possessing fully developed hunting skills.

    However, the overkill hypothesis, as it is termed, has not gone unchallengedfor Australia/New Guinea. Critics emphasize that, as yet, no one has documentedthe bones of an extinct Australian/New Guinean giant with compelling evidenceof its having been killed by humans, or even of its having lived in associationwith humans. Defenders of the overkill hypothesis reply: you would hardlyexpect to find kill sites if the extermination was completed very quicklyand long ago, such as within a few millennia some 40,000 years ago. Thecritics respond with a countertheory: perhaps the giants succumbed insteadto a change in climate, such as a severe drought on the already chronicallydry Australian continent. The debate goes on.

    Personally, I can't fathom why Australia's giants should have survivedinnumerable droughts in their tens of millions of years of Australian history,and then have chosen to drop dead almost simultaneously (at least on atime scale of millions of years) precisely and just coincidentally whenthe first humans arrived. The giants became extinct not only in dry centralAustralia but also in drenching wet New Guinea and southeastern Australia.They became extinct in every habitat without exception, from deserts tocold rain forest and tropical rain forest. Hence it seems to me most likelythat the giants were indeed exterminated by humans, both directly (by beingkilled for food) and indirectly (as the result of fires and habitat modificationcaused by humans). But regardless of whether the overkill hypothesis orthe climate hypothesis proves correct, the disappearance of all of thebig animals of Australia/New Guinea had, as we shall see, heavy consequencesfor subsequent human history. Those extinctions eliminated all the largewild animals that might otherwise have been candidates for domestication,and left native Australians and New Guineans with not a single native domesticanimal.

    Thus, the colonization of Australia/New Guinea was not achieved until aroundthe time of the Great Leap Forward. Another extension of human range thatsoon followed was the one into the coldest parts of Eurasia. While Neanderthalslived in glacial times and were adapted to the cold, they penetrated nofarther north than northern Germany and Kiev. That's not surprising, sinceNeanderthals apparently lacked needles, sewn clothing, warm houses, andother technology essential to survival in the coldest climates. Anatomicallymodern peoples who did possess such technology had expanded into Siberiaby around 20,000 years ago (there are the usual much older disputed claims).That expansion may have been responsible for the extinction of Eurasia'swoolly mammoth and woolly rhinoceros.

    With the settlement of Australia/New Guinea, humans now occupied threeof the five habitable continents. (Throughout this book, I count Eurasiaas a single continent, and I omit Antarctica because it was not reachedby humans until the 19th century and has never had any self-supportinghuman population.) That left only two continents, North America and SouthAmerica. They were surely the last ones settled, for the obvious reasonthat reaching the Americas from the Old World required either boats (forwhich there is no evidence even in Indonesia until 40,000 years ago andnone in Europe until much later) in order to cross by sea, or else it requiredthe occupation of Siberia (unoccupied until about 20,000 years ago) inorder to cross the Bering land bridge. However, it is uncertain when, betweenabout 14,000 and 35,000 years ago, the Americas were first colonized. Theoldest unquestioned human remains in the Americas are at sites in Alaskadated around 12,000 B.C., followed by a profusion of sites in the UnitedStates south of the Canadian border and in Mexico in the centuries justbefore 11,000 B.C. The latter sites are called Clovis sites, named afterthe type site near the town of Clovis, New Mexico, where their characteristiclarge stone spearpoints were first recognized. Hundreds of Clovis sitesare now known, blanketing all 48 of the lower U.S. states south into Mexico.Unquestioned evidence of human presence appears soon thereafter in Amazoniaand in Patagonia. These facts suggest the interpretation that Clovis sitesdocument the Americas' first colonization by people, who quickly multiplied,expanded, and filled the two continents.

    One might at first be surprised that Clovis descendants could reach Patagonia,lying 8,000 miles south of the U.S.-Canada border, in less than a thousandyears. However, that translates into an average expansion of only 8 milesper year, a trivial feat for a hunter-gatherer likely to cover that distanceeven within a single day's normal foraging.

    One might also at first be surprised that the Americas evidently filledup with humans so quickly that people were motivated to keep spreadingsouth toward Patagonia. That population growth also proves unsurprisingwhen one stops to consider the actual numbers. If the Americas eventuallycame to hold hunter-gatherers at an average population density of somewhatunder one person per square mile (a high value for modern hunter-gatherers),then the whole area of the Americas would eventually have held about 10million hunter-gatherers. But even if the initial colonists had consistedof only 100 people and their numbers had increased at a rate of only 1.1percent per year, the colonists' descendants would have reached that populationceiling of 10 million people within a thousand years. A population growthrate of 1.1 percent per year is again trivial: rates as high as 3.4 percentper year have been observed in modern times when people colonized virginlands, such as when the HMS Bounty mutineers and their Tahitian wives colonizedPitcairn Island.

    The profusion of Clovis hunters' sites within the first few centuries aftertheir arrival resembles the site profusion documented archaeologicallyfor the more recent discovery of New Zealand by ancestral Maori. A profusionof early sites is also documented for the much older colonization of Europeby anatomically modern humans, and for the occupation of Australia/NewGuinea. That is, everything about the Clovis phenomenon and its spreadthrough the Americas corresponds to findings for other, unquestioned virgin-landcolonizations in history.

    What might be the significance of Clovis sites' bursting forth in the centuriesjust before 11,000 B.C., rather than in those before 16,000 or 21,000 B.C.?Recall that Siberia has always been cold, and that a continuous ice sheetstretched as an impassable barrier across the whole width of Canada duringmuch of the Pleistocene Ice Ages. We have already seen that the technologyrequired for coping with extreme cold did not emerge until after anatomicallymodern humans invaded Europe around 40,000 years ago, and that people didnot colonize Siberia until 20,000 years later. Eventually, those earlySiberians crossed to Alaska, either by sea across the Bering Strait (only50 miles wide even today) or else on foot at glacial times when BeringStrait was dry land. The Bering land bridge, during its millennia of intermittentexistence, would have been up to a thousand miles wide, covered by opentundra, and easily traversable by people adapted to cold conditions. Theland bridge was flooded and became a strait again most recently when sealevel rose after around 14,000 B.C. Whether those early Siberians walkedor paddled to Alaska, the earliest secure evidence of human presence inAlaska dates from around 12,000 B.C.

    Soon thereafter, a north-south ice-free corridor opened in the Canadianice sheet, permitting the first Alaskans to pass through and come out intothe Great Plains around the site of the modern Canadian city of Edmonton.That removed the last serious barrier between Alaska and Patagonia formodern humans. The Edmonton pioneers would have found the Great Plainsteeming with game. They would have thrived, increased in numbers, and graduallyspread south to occupy the whole hemisphere.

    One other feature of the Clovis phenomenon fits our expectations for thefirst human presence south of the Canadian ice sheet. Like Australia/NewGuinea, the Americas had originally been full of big mammals. About 15,000years ago, the American West looked much as Africa's Serengeti Plains dotoday, with herds of elephants and horses pursued by lions and cheetahs,and joined by members of such exotic species as camels and giant groundsloths. Just as in Australia/New Guinea, in the Americas most of thoselarge mammals became extinct. Whereas the extinctions took place probablybefore 30,000 years ago in Australia, they occurred around 17,000 to 12,000years ago in the Americas. For those extinct American mammals whose bonesare available in greatest abundance and have been dated especially accurately,one can pinpoint the extinctions as having occurred around 11,000 B.C.Perhaps the two most accurately dated extinctions are those of the Shastaground sloth and Harrington's mountain goat in the Grand Canyon area; bothof those populations disappeared within a century or two of 11,100 B.C.Whether coincidentally or not, that date is identical, within experimentalerror, to the date of Clovis hunters' arrival in the Grand Canyon area.

    The discovery of numerous skeletons of mammoths with Clovis spearpointsbetween their ribs suggests that this agreement of dates is not a coincidence.Hunters expanding southward through the Americas, encountering big animalsthat had never seen humans before, may have found those American animalseasy to kill and may have exterminated them. A countertheory is that America'sbig mammals instead became extinct because of climate changes at the endof the last Ice Age, which (to confuse the interpretation for modern paleontologists)also happened around 11,000 B.C.

    Personally, I have the same problem with a climatic theory of megafaunalextinction in the Americas as with such a theory in Australia/New Guinea.The Americas' big animals had already survived the ends of 22 previousIce Ages. Why did most of them pick the 23rd to expire in concert, in thepresence of all those supposedly harmless humans? Why did they disappearin all habitats, not only in habitats that contracted but also in onesthat greatly expanded at the end of the last Ice Age? Hence I suspect thatClovis hunters did it, but the debate remains unresolved. Whichever theoryproves correct, most large wild mammal species that might otherwise havelater been domesticated by Native Americans were thereby removed.

    Also unresolved is the question whether Clovis hunters really were thefirst Americans. As always happens whenever anyone claims the first anything,claims of discoveries of pre-Clovis human sites in the Americas are constantlybeing advanced. Every year, a few of those new claims really do appearconvincing and exciting when initially announced. Then the inevitable problemsof interpretation arise. Were the reported tools at the site really toolsmade by humans, or just natural rock shapes? Are the reported radiocarbondates really correct, and not invalidated by any of the numerous difficultiesthat can plague radiocarbon dating? If the dates are correct, are theyreally associated with human products, rather than just being a 15,000-year-oldlump of charcoal lying next to a stone tool actually made 9,000 years ago?

    To illustrate these problems, consider the following typical example ofan often quoted pre-Clovis claim. At a Brazilian rock shelter named PedroFurada, archaeologists found cave paintings undoubtedly made by humans.They also discovered, among the piles of stones at the base of a cliff,some stones whose shapes suggested the possibility of their being crudetools. In addition, they came upon supposed hearths, whose burnt charcoalyielded radiocarbon dates of around 35,000 years ago. Articles on PedroFurada were accepted for publication in the prestigious and highly selectiveinternational scientific journal Nature.

    But none of those rocks at the base of the cliff is an obviously human-madetool, as are Clovis points and Cro-Magnon tools. If hundreds of thousandsof rocks fall from a high cliff over the course of tens of thousands ofyears, many of them will become chipped and broken when they hit the rocksbelow, and some will come to resemble crude tools chipped and broken byhumans. In western Europe and elsewhere in Amazonia, archaeologists haveradiocarbon-dated the actual pigments used in cave paintings, but thatwas not done at Pedro Furada. Forest fires occur frequently in the vicinityand produce charcoal that is regularly swept into caves by wind and streams.No evidence links the 35,000-year-old charcoal to the undoubted cave paintingsat Pedro Furada. Although the original excavators remain convinced, a teamof archaeologists who were not involved in the excavation but receptiveto pre-Clovis claims recently visited the site and came away unconvinced.

    The North American site that currently enjoys the strongest credentialsas a possible pre-Clovis site is Meadowcroft rock shelter, in Pennsylvania,yielding reported human-associated radiocarbon dates of about 16,000 yearsago. At Meadowcroft no archaeologist denies that many human artifacts dooccur in many carefully excavated layers. But the oldest radiocarbon datesdon't make sense, because the plant and animal species associated withthem are species living in Pennsylvania in recent times of mild climates,rather than species expected for the glacial times of 16,000 years ago.Hence one has to suspect that the charcoal samples dated from the oldesthuman occupation levels consist of post-Clovis charcoal infiltrated witholder carbon. The strongest pre-Clovis candidate in South America is theMonte Verde site, in southern Chile, dated to at least 15,000 years ago.It too now seems convincing to many archaeologists, but caution is warrantedin view of all the previous disillusionments.

    If there really were pre-Clovis people in the Americas, why is it stillso hard to prove that they existed? Archaeologists have excavated hundredsof American sites unequivocally dating to between 2000 and 11,000 B.C.,including dozens of Clovis sites in the North American West, rock sheltersin the Appalachians, and sites in coastal California. Below all the archaeologicallayers with undoubted human presence, at many of those same sites, deeperolder layers have been excavated and still yield undoubted remains of animals--butwith no further evidence of humans. The weaknesses in pre-Clovis evidencein the Americas contrast with the strength of the evidence in Europe, wherehundreds of sites attest to the presence of modern humans long before Clovishunters appeared in the Americas around 11,000 B.C. Even more strikingis the evidence from Australia/New Guinea, where there are barely one-tenthas many archaeologists as in the United States alone, but where those fewarchaeologists have nevertheless discovered over a hundred unequivocalpre-Clovis sites scattered over the whole continent.

    Early humans certainly didn't fly by helicopter from Alaska to Meadowcroftand Monte Verde, skipping all the landscape in between. Advocates of pre-Clovissettlement suggest that, for thousands or even tens of thousands of years,pre-Clovis humans remained at low population densities or poorly visiblearchaeologically, for unknown reasons unprecedented elsewhere in the world.I find that suggestion infinitely more implausible than the suggestionthat Monte Verde and Meadowcroft will eventually be reinterpreted, as haveother claimed pre-Clovis sites. My feeling is that, if there really hadbeen pre-Clovis settlement in the Americas, it would have become obviousat many locations by now, and we would not still be arguing. However, archaeologistsremain divided on these questions.

    The consequences for our understanding of later American prehistory remainthe same, whichever interpretation proves correct. Either: the Americaswere first settled around 11,000 B.C. and quickly filled up with people.Or else: the first settlement occurred somewhat earlier (most advocatesof pre-Clovis settlement would suggest by 15,000 or 20,000 years ago, possibly30,000 years ago, and few would seriously claim earlier); but those pre-Clovissettlers remained few in numbers, or inconspicuous, or had little impact,until around 11,000 B.C. In either case, of the five habitable continents,North America and South America are the ones with the shortest human prehistories.

    With the occupation of the Americas, most habitable areas of the continentsand continental islands, plus oceanic islands from Indonesia to east ofNew Guinea, supported humans. The settlement of the world's remaining islandswas not completed until modern times: Mediterranean islands such as Crete,Cyprus, Corsica, and Sardinia between about 8500 and 4000 B.C.; Caribbeanislands beginning around 4000 B.C.; Polynesian and Micronesian islandsbetween 1200 B.C. and A.D. 1000; Madagascar sometime between A.D. 300 and800; and Iceland in the ninth century A.D. Native Americans, possibly ancestralto the modern Inuit, spread throughout the High Arctic around 2000 B.C.That left, as the sole uninhabited areas awaiting European explorers overthe last 700 years, only the most remote islands of the Atlantic and IndianOceans (such as the Azores and Seychelles), plus Antarctica.

    What significance, if any, do the continents' differing dates of settlementhave for subsequent history? Suppose that a time machine could have transportedan archaeologist back in time, for a world tour at around 11,000 B.C. Giventhe state of the world then, could the archaeologist have predicted thesequence in which human societies on the various continents would developguns, germs, and steel, and thus predicted the state of the world today?

    Our archaeologist might have considered the possible advantages of a headstart. If that counted for anything, then Africa enjoyed an enormous advantage:at least 5 million more years of separate protohuman existence than onany other continent. In addition, if it is true that modern humans arosein Africa around 100,000 years ago and spread to other continents, thatwould have wiped out any advantages accumulated elsewhere in the meantimeand given Africans a new head start. Furthermore, human genetic diversityis highest in Africa; perhaps more-diverse humans would collectively producemore-diverse inventions.

    But our archaeologist might then reflect: what, really, does a "headstart" mean for the purposes of this book? We cannot take the metaphorof a footrace literally. If by head start you mean the time required topopulate a continent after the arrival of the first few pioneering colonists,that time is relatively brief: for example, less than 1,000 years to fillup even the whole New World. If by head start you instead mean the timerequired to adapt to local conditions, I grant that some extreme environmentsdid take time: for instance, 9,000 years to occupy the High Arctic afterthe occupation of the rest of North America. But people would have exploredand adapted to most other areas quickly, once modern human inventivenesshad developed. For example, after the ancestors of the Maori reached NewZealand, it apparently took them barely a century to discover all worthwhilestone sources; only a few more centuries to kill every last moa in someof the world's most rugged terrain; and only a few centuries to differentiateinto a range of diverse societies, from that of coastal hunter-gatherersto that of farmers practicing new types of food storage.

    Our archaeologist might therefore look at the Americas and conclude thatAfricans, despite their apparently enormous head start, would have beenovertaken by the earliest Americans within at most a millennium. Thereafter,the Americas' greater area (50 percent greater than Africa's) and muchgreater environmental diversity would have given the advantage to NativeAmericans over Africans.

    The archaeologist might then turn to Eurasia and reason as follows. Eurasiais the world's largest continent. It has been occupied for longer thanany other continent except Africa. Africa's long occupation before thecolonization of Eurasia a million years ago might have counted for nothinganyway, because protohumans were at such a primitive stage then. Our archaeologistmight look at the Upper Paleolithic flowering of southwestern Europe between20,000 and 12,000 years ago, with all those famous artworks and complextools, and wonder whether Eurasia was already getting a head start then,at least locally.

    Finally, the archaeologist would turn to Australia/New Guinea, noting firstits small area (it's the smallest continent), the large fraction of itcovered by desert capable of supporting few humans, the continent's isolation,and its later occupation than that of Africa and Eurasia. All that mightlead the archaeologist to predict slow development in Australia/New Guinea.

    But remember that Australians and New Guineans had by far the earliestwatercraft in the world. They were creating cave paintings apparently atleast as early as the Cro-Magnons in Europe. Jonathan Kingdon and Tim Flanneryhave noted that the colonization of Australia/New Guinea from the islandsof the Asian continental shelf required humans to learn to deal with thenew environments they encountered on the islands of central Indonesia--amaze of coastlines offering the richest marine resources, coral reefs,and mangroves in the world. As the colonists crossed the straits separatingeach Indonesian island from the next one to the east, they adapted anew,filled up that next island, and went on to colonize the next island again.It was a hitherto unprecedented golden age of successive human populationexplosions. Perhaps those cycles of colonization, adaptation, and populationexplosion were what selected for the Great Leap Forward, which then diffusedback westward to Eurasia and Africa. If this scenario is correct, thenAustralia/New Guinea gained a massive head start that might have continuedto propel human development there long after the Great Leap Forward.

    Thus, an observer transported back in time to 11,000 B.C. could not havepredicted on which continent human societies would develop most quickly,but could have made a strong case for any of the continents. With hindsight,of course, we know that Eurasia was the one. But it turns out that theactual reasons behind the more rapid development of Eurasian societieswere not at all the straightforward ones that our imaginary archaeologistof 11,000 B.C. guessed. The remainder of this book consists of a questto discover those real reasons.

Footnote:(*) Throughout this book, dates for about the last 15,000 years willbe quoted as so-called calibrated radiocarbon dates, rather than as conventional,uncalibrated radiocarbon dates. The difference between the two types ofdates will be explained in Chapter 5. Calibrated dates are the ones believedto correspond more closely to actual calendar dates. Readers accustomedto uncalibrated dates will need to bear this distinction in mind wheneverthey find me quoting apparently erroneous dates that are older than theones with which they are familiar. For example, the date of the Clovisarchaeological horizon in North America is usually quoted as around 9000B.C. (11,000 years ago), but I quote it instead as around 11,000 B.C. (13,000years ago), because the date usually quoted is uncalibrated.]FNT (*) Throughoutthis book, dates for about the last 15,000 years will be quoted as so-calledcalibrated radiocarbon dates, rather than as conventional, uncalibratedradiocarbon dates. The difference between the two types of dates will beexplained in Chapter 5. Calibrated dates are the ones believed to correspondmore closely to actual calendar dates. Readers accustomed to uncalibrateddates will need to bear this distinction in mind whenever they find mequoting apparently erroneous dates that are older than the ones with whichthey are familiar. For example, the date of the Clovis archaeological horizonin North America is usually quoted as around 9000 B.C. (11,000 years ago),but I quote it instead as around 11,000 B.C. (13,000 years ago), becausethe date usually quoted is uncalibrated.