The Dawn of Human Culture (29 page)

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the great difference between the mtDNA recovered from three different Neanderthal individuals and the mtDNA of living people. The mtDNA from the Mungo 3 skeleton resembles that of living people far more closely, and it need represent only a type that became extinct after modern humans spread from Africa.

The history of early Australian colonization raises more difficult questions. During glacial periods when vast amounts of water were locked in the ice caps, sea level fell by 100 meters (330 feet) or more, and New Guinea, Tasmania, and Australia were joined in a land mass christened Greater Australia (or Sahul Land) (Figure 7.11). However, Australia was never connected to southeastern Asia (Sunda Land), and even when sea level was lowest, newcomers to Australia would have had to cross at least 80 kilometers (50 miles) of open water. Arguably, only modern people could have invented sufficiently seaworthy water-craft, and if they spread from Africa only after 50,000 years ago, Australia could not have been colonized before this time.

Until the early 1990s, it appeared that the first Australians were in fact fully modern people who arrived between 40,000 and 30,000

years ago, bringing with them complex burial practices, fishing technology, art, and probably other modern behavioral markers. Now, two sets of dates suggest that people had reached Australia by 60,000 years ago or even before. The first are luminescence determinations between 60,000 and 50,000 years ago on quartz sands that enclose stone artifacts at Malakunanja II and Nauwalabila I in northern Australia. The second are uranium (or U-) series and ESR ages averaging 62,000 years ago on elements of human skeleton number 3 from the Lake Mungo site in southeastern Australia. Bert Roberts of La Trobe University (Melbourne) and his colleagues produced the Malakunanja II and Nauwalabila I ages, 07 Body before Behavior.r.qxd 1/29/02 5:06 PM Page 248

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N

Pacific

Ocean

SUNDA

Ngandong

SAHUL

Nauwalabila I

Malakunanja II

Indian

Ocean

Lake Mungo

0

1000 mi

0

2000 km

FIGURE 7.11

Australia and southeast Asia, with the archeological sites mentioned in the text. Present-day land-masses are outlined in black. Additional land that would be exposed by a 200-meter (660-foot) drop in sea level is shown in white.

while Rainer Grün of the Australian National University (Canberra) and his colleagues provided the Lake Mungo dates. The Mungo 3 age of 62,000 years is particularly significant, because the skeleton represents 07 Body before Behavior.r.qxd 1/29/02 5:06 PM Page 249

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a fully modern person, and it lay in a grave that recalls many European Upper Paleolithic examples in the layout of the body and in the abundance of powdered red ochreous pigment. Upper Paleolithic-like (fully modern) behavior is perhaps also implied by the need to import the ocher from as far as 200 kilometers (120 miles) away.

We have already outlined the principles behind luminescence and ESR dating. The U-series method depends on the observation that uranium occurs naturally in small quantities virtually everywhere and that it is soluble in water, while products of its radioactive decay, thorium and protactinium, are not. Thus, when uranium precipitates from groundwater, as for example in a newly formed stalagmite, the stalagmite will initially contain no daughter products, but these will subsequently accumulate inside at a rate that is directly proportional to the rate at which uranium decays. The ratios between the daughter products and uranium can then be used to estimate the time when the uranium precipitated from groundwater, meaning, in the case of a stalagmite, the time when it formed.

U-series dating is most reliable when it is applied to stalagmites or similar substances that subsequently remained closed to the addition or subtraction of uranium. In theory, it can be applied to fossil bone, since fresh bone contains little or no uranium, and the uranium in a fossil must then have been adsorbed from groundwater after burial. The timing and rate of adsorption, however, are generally unknowable, and adsorption can even alternate with loss (leaching). There is thus usually no way to set the clock to zero to determine when the bone was buried.

U-series dates on bones from a single layer often scatter widely, and different dates have even been obtained on parts of the same bone.

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The occupation of Australia by modern humans at or before 60,000 years ago would argue not only against a radical behavioral shift between 50,000 and 40,000 years ago, it would also require modifications to the more fundamental hypothesis that modern humans originated in Africa. Minimally, it would call for at least two separate expansions of modern Africans, an earlier one perhaps across the southern end of the Red Sea to southern Asia and then to Australia, and a later one perhaps through the Sinai Desert of Egypt to western Asia and then to Europe. It might also mean that the modern human expansion to Australia somehow bypassed nearby Indonesia, since we pointed out in Chapter 4 that ESR dates on associated animal teeth suggest that the famous Ngandong (or Solo River) human fossils date from 50,000 years ago or later. The Ngandong fossils clearly do not represent modern people, and they have been assigned to an evolved variety of
Homo erectus
.

The early Australian dates are revolutionary if they are correct, but they have encountered serious skepticism. Archeologists Jim O’Connell of the University of Utah and Jim Allen of La Trobe University have questioned the Malakunanja II luminescence dates, because the sands on which they are based lay less than 50 centimeters (20 inches) below a layer dated to 22,000 to 20,000 years ago by radiocarbon. The implication is that the sands accumulated very slowly between about 60,000 and 20,000 years ago, and this raises the possibility that bioturbation (the activity of living organisms in the soil) displaced much younger artifacts downwards. Termites, which are common in the region, are known to produce sufficient downward displacements elsewhere. At Nauwalabila I, stratigraphic inconsistency in the available radiocarbon dates underscores the possibility that bioturbation caused downward movement.

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Bert Roberts has challenged the validity of the 62,000 years date for Mungo 3, even though this age would broadly support the Malakunanja II and Nauwalabila I luminescence dates for which he was primarily responsible. The main problem at Lake Mungo is the common one—the possibility or even likelihood that the human bones have experienced a complex history of uranium uptake and loss after burial. This would not only confound U-series dating, it could also mislead ESR, which depends intimately on the same uranium signal.

Geomorphologist Jim Bowler of the University of Melbourne, who discovered the Mungo 3 skeleton in 1974, has voiced an even more basic objection. Luminescence and other dates from samples that were carefully selected in the field indicate that Mungo 3 was buried into sediments that accumulated in the interval between 46,000 and 40,000

years ago. The skeleton could then be no older than this.

In sum, human arrival in Australia before 50,000 years ago is far from proven, and pending fresh, more conclusive dates, Australia does not provide a compelling reason to rethink either the time when the LSA appeared or to modify other important aspects of the Out-of-Africa hypothesis.

* * *

If as we believe, the first Australians descended from Africans who had achieved a fully modern level of hunting-gathering competence, their arrival in Australia might have proven catastrophic for the local fauna.

Bert Roberts and his colleagues have in fact recently published dates which suggest that many large Australian marsupials and reptiles disappeared abruptly about 46,000 years ago. They argue that a human 07 Body before Behavior.r.qxd 1/29/02 5:06 PM Page 252

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cause is more likely than a climatic one, since climate was relatively stable at the time.

The initial arrival of people has also been blamed for a similar wave of large animal extinctions that occurred in the Americas between 12,000 and 10,000 years ago. The American case is more complicated than the Australian one, because the extinctions coincided with the period of rapid climatic change from the Last Glaciation to the Present Interglacial. Still, the extinct species had survived earlier glacial/interglacial transitions, and a human role seems particularly likely given the advanced hunting-gathering skills that the earliest Americans surely brought with them from Asia.

Finally, advanced Upper Paleolithic and LSA hunter-gatherers could have precipitated the demise of a few large mammal species in Eurasia and Africa between 12,000 and 10,000 years ago. As in the Americas, adverse climatic change may have contributed, but the extinct species had survived similar changes earlier on, and the only conspicuous difference 12,000 years ago was the presence of much more sophisticated hunters. Many fewer species became extinct in Eurasia and Africa than in the Americas and Australia, but then the Eurasian and African faunas had evolved with humans, and they were surely much less naïve.

If late Paleolithic people in Australia, the Americas, and Eurasia reduced species diversity in the way the data suggest, then the dawn of human culture represents not only a profound behavioral or sociocultural transition. It also marks the transformation of humanity from a relatively rare and insignificant member of the large mammal fauna to a geologic force with the power to impoverish nature. In short, from early on, the modern human ability to innovate may been both a blessing and a curse.

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* * *

The Australian case is a potent reminder that a comprehensive theory of modern human origins must also embrace the Far East (eastern Asia). Genetics and above all the Y-chromosome study that we previously cited argue strongly that living Far Easterners share a recent African ancestor with all other living humans, but the Far Eastern fossil and archeological records provide less support. The problem is not that they present contrary evidence, but that they present very little evidence at all.

We have already summarized fossils and dates that suggest that
Homo erectus
persisted in Indonesia until perhaps 50,000 years ago. The dates are questionable because they were obtained by the ESR method, but if they are confirmed by future research, they would clearly be consistent with a recent African origin for modern southeast Asians.

The east Asian mainland has provided few fossils that postdate classic
erectus
after 500,000 to 400,000 years ago. The most important specimens include skulls from the Chinese sites of Dali, Yinkou (Jinnuishan), and Maba, all of which have been tentatively dated to between 200,000 and 100,000 years ago. The skulls variably combine massive browridges, low, flat, receding foreheads and other primitive features that mark
erectus
with more rounded braincases, less massive faces, and other advanced features that mark
Homo sapiens
(Figure 7.12). The Chinese skulls differ both from contemporaneous Neanderthal skulls in Europe and from early modern or near-modern skulls in Africa, but in their mix of archaic and derived features, they recall the 600,000- to 400,000-year-old African and European fossils that we previously assigned to
Homo heidelbergensis
. This could imply 07 Body before Behavior.r.qxd 1/29/02 5:06 PM Page 254

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flat, receding

forehead

strongly

developed

large,

browridge

relatively

well rounded

braincase

broad nasal

bridge

broad,

flat face

0

5 cm

shoveled

incisor

reduced

0

2 in

third molar

Yinkou (Jinniushan)

FIGURE 7.12

A human skull from Yinkou (Jinniushan), northeastern China (drawn by Kathryn Cruz-Uribe from a photograph) (Copyright Kathryn Cruz-Uribe).

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that
heidelbergensis
extended its range to China after it had disappeared on the west, or it might mean that Chinese
erectus
and African/

European
heidelbergensis
evolved similar features independently.

We favor independent (parallel) evolution, if only because the Chinese archeological record reveals no evidence for a population incursion like the one that brought Acheulean hand axes from Africa to Europe. We suggested previously that the hand axes may mark the spread of
heidelbergensis
. In addition, the later Chinese fossils tend to resemble Chinese
erectus
in a handful of features, such as the shortness of the upper jaw, the flatness and horizontal orientation of the cheekbones, the great breadth of the nasal bridge, the shovel-like shape of the upper incisor teeth, and the small size of the third molars. If independent evolution is accepted, then Chinese and Indonesian
erectus
followed separate evolutionary trajectories, and Chinese
erectus
might have to be relegated to a separate species. The more important point here is that the Chinese fossil record by itself is too meager to confirm or reject an African origin for modern east Asians.

The associated Chinese archeological record is even sparser, and the Indonesian record is nonexistent. We predict that when archeological observations become more abundant in eastern Asia, they will reveal the same rupture between 50,000 and 37,000 years ago that we have observed in Africa and Europe, involving the first appearance of art, well-made bone, ivory, and shell artifacts, complex graves, and other modern behavioral traits. In the meanwhile, except again for the genetics, the pattern of modern human origins must be decided almost exclusively on evidence from the Far West. Decades of research have left little doubt about the rupture there, but they have yet to reveal why it occurred.