The Dawn of Human Culture (25 page)
“contamination,” and their impact will be especially great on objects that are older than 20,000 to 25,000 years. Such objects will retain very little of their original 14C, and the addition of even a small amount of more recent carbon will increase their 14C content significantly, producing an apparent radiocarbon age that is much too young. It can be shown mathematically that just a one percent increment of modern carbon to a sample that is actually 67,000 years old will make the sample appear to be only 37,000 years old, and no laboratory can guarantee to remove such tiny amounts of contaminant. Contamination is particularly likely to affect degraded bone protein, and it is less likely to affect charcoal. Unfortunately, charcoal is relatively rare in sites older than 25,000 years ago, and bone dates predominate heavily. The bottom line is that on radiocarbon alone, it can rarely be said that a site dated to 30,000 years ago is not actually 5000, 10,000, or even 20,000 years older. And it is here that we confront the problem of dating the last Neanderthals.
The radiocarbon method has been applied directly to
Neanderthal bones at Mezmaiskaya Cave (Russia) and Vindija (Croatia), both of which we have already cited for their provision of Neanderthal DNA. At Mezmaiskaya, the radiocarbon result implies that a 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 212
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Neanderthal infant died about 29,000 years ago, while at Vindija, it suggests that Neanderthals persisted locally until 29,000 to 28,000 years ago. If the Mezmaiskaya and Vindija dates are taken at face value, Neanderthals co-existed with early Upper Paleolithic people in each region for at least 6000 to 7000 years, and we might conclude that Neanderthals often held their own against Cro-Magnon invaders. On the other hand, if the bones at both sites were only minutely contaminated by much more recent carbon, they could easily be 8000 to 10,000 years older, and we wouldn’t need to infer any overlap with Cro-Magnons.
Given the ever-present potential for contamination, particularly in bone protein, many specialists routinely regard radiocarbon dates older than 25,000 or 30,000 years as only minimum ages, meaning that the dated specimens could be the stated age or much older. When potential contamination is taken into account, a useful rule of thumb is that where dates depart from stratigraphic order within a site (that is, when dates from the same layer differ or when they fail to become older with depth), the oldest dates probably most closely approximate the true age.
Mezmaiskaya Cave illustrates the point, for it has provided a radiocarbon date of 32,000 years on wood charcoal from an Upper Paleolithic layer that is stratified above the layer with the Neanderthal infant. The implication is that the infant must actually be older than 32,000 years, and Mezmaiskaya does not show that Neanderthals and modern people overlapped for thousands of years in southern Russia.
Given the ever present problem of contamination, it follows that the best estimate for when the Neanderthals succumbed will come not from the youngest Mousterian (or Neanderthal) dates but from the oldest Upper Paleolithic ones. The comprehensive analysis by João Zilhão and Francesco d’Errico indicates that the early Upper Paleolithic Aurignacian Culture 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 213
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intruded into western and central Europe about 37,000 to 36,000 years ago. And in most places, site stratigraphies indicate that whatever the date, early Upper Paleolithic Cro-Magnons quickly replaced Mousterian Neanderthals, probably within centuries or a millennium. We stress “most places,” because there is one well-publicized, putative exception.
The exception to quick replacement involves the Iberian cul-de-sac, meaning Spain and Portugal south of the Ebro and Tagus Rivers.
Three Spanish sites north of the Ebro have provided early Aurignacian dates near 40,000 years ago, but Zilhão and d’Errico believe that in each case the dated material was actually associated with older Mousterian or perhaps Châtelperronian artifacts, and they place the earliest local Aurignacian closer to 37,000 years ago. Even then, however, it would be 7000 to 8000 years older than any dated Upper Paleolithic south of the Ebro and Tagus. Equally important, some southern Spanish and Portuguese Mousterian sites have produced radiocarbon dates ranging up to 30,000 years ago. The most striking dates are from Zafarraya Cave, where they were obtained directly on Neanderthal bones. To Zilhão, d’Errico, and others, the sum means that Neanderthals found refuge on the Iberian Peninsula long after modern humans had displaced them elsewhere in Europe. There is an alternative interpretation, however. First, the Iberian late Mousterian/ Neanderthal dates are still few, and as always, it is possible that they are only minimum age estimates. Second, the absence of the Upper Paleolithic before 30,000 years ago may mean only that much of the Iberian Peninsula was sparsely populated or even abandoned from before 37,000 years ago until 30,000 years ago or later.
The reason would be adverse climate. Archeological layers that fall unequivocally between 40,000 and 20,000 years ago are rare or absent in northwestern Africa, just across the Straits of Gibraltar, and the 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 214
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reason appears to have been persistent, extreme aridity. The question of how long Neanderthals survived in Iberia differs from the Châtelperronian issue, because it can be resolved by additional research.
In the meanwhile, we see no compelling reason to suppose that Neanderthals persisted anywhere in Europe long after modern humans had appeared.
* * *
What about Neanderthal language? The truth is that we don’t know. We can only imagine that Neanderthals had a system that was far more complex than that of chimpanzees or for that matter than the systems of the australopiths,
Homo ergaster,
and probably even
Homo heidelbergensis
. But does that mean it was as sophisticated as modern language?
One clue may come from the position of the voice box (or larynx), which is crucial for the production of the entire range of sounds that all modern languages require. In apes and newborn humans, the voice box is located high in the throat, restricting the range of possible sounds. A major advantage of this position is that it permits apes and human infants to swallow 06 Neanderthals.r.qxd 1/29/02 5:05 PM Page 215
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and breathe at the same time, reducing the risk of choking. The voice box begins its descent in humans between the ages of 11⁄2 and 2 years, and since this significantly increases the risk of choking, there must be a counter-vailing natural selective benefit. The most obvious one is the newly created ability to produce all the sounds that are essential for phonemic speech, and no one doubts the survival benefit of speech. The position of the voice box is related to the shape of the skull base—flat in apes and modern human infants and arched upwards or flexed in modern human adults. On the three Neanderthal skulls that are well enough preserved to show the skull base, it appears to have been flat, and this might mean that Neanderthals could not have produced speech as we know it.
Against this, however, we must consider the tongue bone (or hyoid), which provides hard support for the voice box and which differs significantly in shape between apes and modern humans. Only a single tongue bone is known for the Neanderthals, but it’s a dead ringer for its modern human counterpart. And we must also consider the Neanderthals’ African contemporaries—the modern or near-modern people, who, unlike the Neanderthals, included our ancestors. They had flexed cranial bases, but we will see that in virtually every detectable archeological respect they were no more modern than the Neanderthals.
So, if they could speak in a fully modern way, the ability doesn’t seem to have fostered full-blown modern behavior—the dawn of human culture to which the title of this book refers. A newly found capacity for language may still have prompted fully modern behavior, but if so the capacity must have been rooted in a brain change. We argue later that such a brain change is the most economic explanation for why modern human behavior emerged and spread so abruptly.
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* * *
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7
BODY BEFORE BEHAVIOR
Raymond Dart ignited the search for human origins in Africa when he announced the Taung child’s skull in 1925, but it was not the first significant human fossil to emerge from Africa. Already in 1921, lead-and-zinc miners had recovered a remarkable skull from a cave at the Broken Hill Mine in Northern Rhodesia. The skull exhibited a flat, receding forehead above a thick browridge and a massive face. Yet it possessed typically human teeth, and its braincase approached modern ones in size. The teeth were remarkable mainly for their advanced decay, associated with infection (abscessing) that penetrated the jaw bone. Spread of the infection before death possibly produced a partially healed puncture on the skull wall.
The mining company transferred the skull to London, and in 1922, the distinguished anatomist Arthur Smith Woodward presented it to a meeting of the Anatomical Society. Dart was present, and he later 07 Body before Behavior.r.qxd 1/29/02 5:06 PM Page 218
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recalled, “It was a staggering sight to see an undoubtedly human skull with beetling eyebrow ridges thicker than those of Neanderthal Man and a muzzle as massive as that of a gorilla. Yet the teeth were like those of any modern man and the brain quite large (1,280 cc).” The skull has sometimes been likened to those of the Neanderthals, but it differed from Neanderthal skulls in numerous respects, including its great breadth near the base, the relatively large size of its mastoid process, and the absence of an oval depression just above the upper limit for the attachment of the neck muscles (Figure 7.1). Woodward assigned the skull to the species
Homo rhodesiensis,
which the popular press quickly translated as “Rhodesian Man.” The specimen is still housed in London, but in 1964, Northern Rhodesia gained independence as Zambia, and Broken Hill became Kabwe (Figure 7.2). The fossil is thus now usually known as the Kabwe skull.
The Kabwe skull exemplifies an all-too-frequent paradox in paleoanthropology—the skull might never have been found without intensive commercial activity, yet the same activity all but erased key stratigraphic information. The miners recovered animal bones and some other less spectacular human remains from the same cave, but we do not know which, if any, were in the same layer as the skull. We also do not know if there were artifacts nearby, although it seems likely that there were.
Paleoanthropologists rely on associated artifacts and animal species for many purposes, not the least of which is to gauge the relative age of important human fossils. And it goes without saying that fossils lose much of their value if they cannot be arranged in time. The circumstances of discovery at Kabwe preclude secure dating, but the miners recovered bones of some archaic mammal species, and if we assume that these occurred with the skull, they suggest it is between 700,000 and 400,000
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no depressed area of
roughened bone on the back
flat, receding
of the skull
forehead
thick
browridge
partially healed
puncture
juxtamastoid
crest
skull broadest near the base
mastoid
process
Kabwe (Broken Hill)
0
5 cm
depressed area of
roughened bone on
the back of the skull
0
2 in
juxtamastoid
mastoid
crest
skull bulges outwards above the base
process
Neanderthal
(La Ferrassie 1)
FIGURE 7.1
The fossil human skull from Kabwe, Zambia, compared to the skull of a Neanderthal from La Ferrassie, France (redrawn after A. P. Santa Luca 1978,
Journal of Human Evolution
7, p. 623 pp.
622, 626).
years old. In this event, it would be roughly contemporaneous with three similar, more recently found African specimens. These come from Bodo in 07 Body before Behavior.r.qxd 1/29/02 5:06 PM Page 220
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