The Dawn of Human Culture (24 page)

Duarte and her colleagues invited human paleontologist Erik Trinkaus of Washington University to analyze the skeleton with them.

The state of the dentition indicated that the child was about 4 years old when it died, and in virtually all respects, the bones closely resembled those of a modern 4-year-old. There was no surprise in that, given the 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 203

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Gravettian dating. However, Trinkaus and the Portuguese scientists also detected what they believe are two Neanderthal traits: the backwards slope of the bone below the incisor teeth at the front of the lower jaw and, especially, the shortness of the shin bone (tibia) relative to the thigh bone (femur). Recall that short shin bones are a typical Neanderthal feature and they are an important part of the reason why Neanderthals are thought to have been physiologically adapted to cold.

In June 1999, Duarte, Trinkaus, and their colleagues published their findings in the
Proceedings of the National Academy of Sciences,
and they concluded that the Lagar Velho child demonstrated that Neanderthals and modern humans interbred.

In an accompanying commentary, anthropologists Ian Tattersall of the American Museum of Natural History and Jeffrey Schwartz of the University of Pittsburgh were skeptical. They pointed out that the child’s anatomy was overwhelmingly modern and that the skeleton showed no features that are unique to the Neanderthals. In addition, they argued that only a first- or second-generation hybrid would likely show a clear mix of discrete modern and Neanderthal traits, while the Lagar Velho child had lived and died at least 200 generations after the last Neanderthals in Portugal or Spain. They concluded that the proposed hybrid was “simply a chunky Gravettian child, a descendant of the modern invaders who had evicted the Neanderthals from Iberia several millennia earlier.” No one has formally polled anthropologists on the question, but most would probably accept this conclusion. DNA might provide further insight if it could be extracted from the child’s bones, but the prospects appear poor, because the bones do not preserve remnants of original protein.

Other evidence for hybridization is even more dubious, but the earliest Cro-Magnons were often remarkably robust, and in that sense, they 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 204

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sometimes recall the Neanderthals. The Aurignacian people who lived near Mladeč in the Czech Republic are prime examples, but Günter Bräuer of the University of Hamburg and his colleague Helmut Broeg recently scrutinized their skulls and failed to detect a single Neanderthal specialization. Nor did they find any in some slightly younger Czech skulls. Excepting perhaps Lagar Velho then, like the genes of living humans, early Upper Paleolithic skeletal remains suggest that if Cro-Magnons and Neanderthals interbred, it was probably on a very small scale.

* * *

Of course, even if early Cro-Magnons and Neanderthals did not exchange genes, they surely saw each other, and some contact would have been inevitable. Across Europe, artifacts far outnumber human fossils, and we might reasonably ask if these ever suggest interaction. The answer is mainly no. At most sites that contain both Mousterian and Upper Paleolithic layers, the Upper Paleolithic layers overlie the Mousterian ones with no evidence for either population contact or a substantial gap in time. The sum suggests that Cro-Magnons replaced Neanderthals in a geologic eye blink, and we think that in most regions that’s exactly what happened. There are, however, occasional exceptions—those unusual sites with a mix of Mousterian and Upper Paleolithic artifacts that cannot be explained simply by poor excavation. Such sites unquestionably exist, and they are a major thorn in the side of the claim that Neanderthals were biologically precluded from behaving in a modern human fashion.

The principal sites occur in a restricted area of northern Spain and western and central France (west of the Rhône River), where archeologists assign them to the Châtelperronian Industry or Culture (Figure 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 205

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Aurignacian

Châtelperronian

Uluzzian

0

500 km

Szeletian/

Jerzmanowician

0

500 miles

FIGURE 6.8.

The geographic distribution of the early Upper Paleolithic Aurignacian Culture and of the preceding Châtelperronian, Uluzzian, and Szeletian/Jerzmanowician cultures (redrawn after P. A.

Mellars 1993, in
The Origin of Modern Humans and the Impact of Chronometric Dating
, Princeton University Press: Princeton, NJ, fig. 1).

6.8). In deeply stratified deposits, Châtelperronian layers directly overlie Mousterian layers, and they are covered in turn by layers with artifacts from the early Upper Paleolithic Aurignacian culture. All known Aurignacian human fossils, including, for example, those from the Mladeč site, represent fully modern Cro-Magnons, and even the earliest Aurignacian artifact assemblages contain indisputable, often spectacular art objects and well-made bone implements. Radiocarbon dating of charcoal incorporated in pigment has now shown that Aurignacian people also painted on cave walls. Dates on the Châtelperronian and the early Aurignacian overlap significantly, and the time difference between the two may have been too brief to measure with current methods. At the moment, a reasonable inference is that the Châtelperronian began 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 206

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about 45,000 years ago and that it persisted until perhaps 36,000 years ago, when the Aurignacian had already appeared nearby. Human remains from caves at Saint-Césaire and Arcy-sur-Cure, France, show that Châtelperronian people were Neanderthals. At both sites, the Châtelperronian occupations are among the latest known, and the people were probably among the last Neanderthals.

If only stone artifacts were involved, the Châtelperronian might be considered simply a kind of final Mousterian, and the earlier part of the Châtelperronian, before 37,000 to 38,000 years ago, may have been no more than that. At Arcy-sur-Cure, however, Châtelperronian people not only produced a mix of Mousterian and Upper Paleolithic stone artifact types, they also manufactured quintessential Upper Paleolithic bone tools and personal ornaments (Figure 6.9). The Châtelperronian layers provided 142 bone implements, including some that appear to have been decorated, and 36 animal teeth and pieces of ivory, bone, or shell that were pierced or grooved for hanging as beads or pendants. Nearly identical pierced teeth have also been found in the Châtelperronian layers of Quinçay Cave, France. Francesco d’Errico has shown that the Arcy Châtelperronians manufactured their bone artifacts and ornaments on the spot and that they employed their own distinctive techniques.

At Arcy, the Châtelperronians also modified their living space to an extent that is common only in the Upper Paleolithic. The Châtelperronian layers contain traces of several “hut emplacements,”

FIGURE 6.9

Châtelperronian artifacts from the Grotte du Renne (“Reindeer Cave”) at Arcy-sur-Cure, France.

In general, only Upper Paleolithic Cro-Magnons manufactured well-formed burins, bone artifacts, and pendants, yet the people who left such artifacts in the Châtelperronian layers of the Grotte du Renne appear to have been Neanderthals.

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Châtelperronian points (backed knives)

burins

incised grooves

encircling tooth roots

modified animal teeth (“pendants”)

0

5 cm

0

2 in

Grotte du Renne,

Arcy-sur-Cure

bone artifacts

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of which the best preserved is a rough circle of eleven postholes enclosing an area 3 to 4 meters (10 to 13 feet) across that was partially paved with limestone plaques. Pollen recovered from the Arcy deposits indicates that wood was rare nearby, and the postholes probably supported mammoth tusks, which are more numerous in the Arcy site than in any other Paleolithic cave.

João Zilhão and Francesco d’Errico have argued that the Neanderthals independently invented the Châtelperronian, but the most persuasive Upper Paleolithic elements appear only near its very end. This suggests to us and others that the Châtelperronians borrowed the underlying concepts from early Aurignacian Cro-Magnon neighbors. Zilhão’s and d’Errico’s careful analysis of all the available dates indicates that the Aurignacian Culture penetrated central and western Europe 36,000 to 37,000 years ago, when the late Châtelperronian flowered. The late Châtelperronian didn’t last long, and by 35,000 years ago, only the Aurignacian survived.

Archeologists in Italy and Central Europe have proposed cultures called the Uluzzian and Szeletian/Jerzmanowician that they think may also reflect early Upper Paleolithic influence on Neanderthals (Figure 6.8), and future research may show that one or both are as compelling as the Châtelperronian. Still, even if the Châtelperronian remains unique, it presents us with a problem, for if Neanderthals could imitate Upper Paleolithic culture, they were not biologically precluded from behaving in an Upper Paleolithic way. And if, as we believe, Upper Paleolithic culture was superior (meaning minimally that it promoted larger human populations), Neanderthals should have acculturated more widely, and we would expect their anatomical traits and their genes to be more obvious in later populations. In sum, we see the Châtelperronian as the biggest obstacle to our ideas about how and why the Neanderthals disappeared.

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* * *

In Chapter 1, we noted that a key modern behavioral marker—art in the form of jewelry—appeared in eastern Africa before 40,000 years ago, and we have just noted that art and other modern behavioral markers appeared in central and western Europe only about 37,000 to 36,000

years ago. This is, of course, an expected difference if anatomically modern Africans had to develop modern behavior before they could expand to Europe. However, we may still ask how quickly modern human invaders replaced the Neanderthals. Did the Neanderthals manage to hold on longer in some places than in others and might this imply that we have underestimated their behavioral capabilities? If Neanderthals and modern humans overlapped for a long time in some regions, wouldn’t that increase the likelihood that they interbred, or at least that they exchanged culture? The issue of timing might seem straightforward, but it’s actually quite complex. The core problem is the difficulty of obtain-ing reliable dates between 60,000 and 30,000 years ago. Virtually everyone agrees that before 60,000 years ago, the Neanderthals were alone in Europe and that after 30,000 years ago they were gone.

The famous radiocarbon method has long been and still is the principal available technique for dating the demise of the Neanderthals.

Chemist Willard Libby and his colleagues developed the method at the University of Chicago in the late 1940s, and it is no exaggeration to say that its widespread application afterwards revolutionized archeology. In recognition of his achievement, Libby himself was awarded a Nobel Prize. The reasoning behind the method is elegant and clear-cut.

The abundant element carbon (C) occurs naturally in three varieties or isotopes—12C, 13C, and 14C. For present purposes we can ignore 13C and 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 210

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concentrate on 12C, which is by far the most abundant of the three isotopes, and on 14C, which is much rarer. Unlike 12C, 14C is radioactive, and it decays with a half-life of about 5730 years, which means that after 5730 years, any given amount will be reduced by half (through decay to Nitrogen 14 or 14N). This half-life may seem long, but it is very short by comparison to that of many other radioactive isotopes, including, for example, radiopotassium or 40K, whose half-life is approximately 1.3 billion years. The potassium/argon dating technique depends on 40K, and its slow decay rate explains why potassium/argon is useful for dating ancient volcanic rocks like those at the east African australopith sites that are millions of years old. 14C would be useless for the same purpose, because even if suitable material were available, 14C’s short half-life means that after just a few tens of thousands of years—perhaps 100,000 at the outside—it will be too meagerly represented for accurate measurement.

14C would essentially disappear from the planet, except that the interaction between cosmic rays and 14N constantly creates a new supply in the upper atmosphere. In general, plants obtain their carbon directly from the atmosphere (from carbon dioxide), and animals obtain theirs from ingesting plants or other animals. Plants and animals ordinarily do not discriminate between 14C and 12C when they build their tissues, which means that the 14C/12C ratio in live creatures approximates the ratio in the atmosphere. When an organism dies, however, it ceases to assimilate carbon, and the ratio of 14C to 12C

decreases at a rate that is directly proportional to the half-life of 14C.

This means that the 14C/12C ratio in ancient organic matter, such as a piece of charcoal or the degraded protein (collagen) extracted from bone, can be used to estimate when the organism—tree or animal—died.

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In practice, the radiocarbon method confronts numerous complications, including well-documented variation in the atmospheric content of 14C through time, probably caused mainly by fluctuations in cosmic ray intensity. In the context of dating the last Neanderthals, the biggest challenge stems from 14C’s short half-life and the possibility that an ancient piece of organic matter acquired some of its carbon in the ground, after burial. Humic acids (decayed plant matter) percolating down from the surface are probably the most frequent source of such