National Geographic : 2008 Oct
dangerous business," write Stiner and Kuhn, judging by the many healed fractures evident on Neanderthal upper limbs and skulls. The mod ern human bands that arrived on the landscape toward the end of the Neanderthals' time had other options. "By diversifying diet and having personnel who [did different tasks], you have a formula for spreading risk, and that is ultimately good news for pregnant women and for kids," Stiner told me. "So if one thing falls through, there's some thing else." A Neanderthal woman would have been powerful and resilient. But without such cultural buffering, she and her young would have been at a disadvantage. Of all possible cultural buffers, perhaps the most important was the cushion of society itself. According to Erik Trinkaus, a Neanderthal social unit would have been about the size of an extended family. But in early modern human sites in Europe, Trinkaus said, "we start getting sites that represent larger populations." Simply living in a larger group has biological as well as social repercussions. Larger groups inevitably demand more social interactions, which goads the brain into greater activity during childhood and ado lescence, creates pressure to increase the sophis tication of language, and indirectly increases the average life span of group members. Longevity, in turn, increases intergenerational transmission of knowledge and creates what Chris Stringer calls a "culture of innovation"-the passage of practical survival skills and toolmaking technol ogy from one generation to the next, and later between one group and another. Whatever the suite of cultural buffers, they may well have provided an extra, albeit thin, layer of insulation against the harsh climatic stresses that Stringer argues peaked right around the time the Neanderthals vanished. Ice core data suggest that from about 30,000 years ago until the last glacial maximum about 18,000 years ago, the Earth's climate fluctuated wildly, sometimes within the space of decades. A few more people in the social unit, with a few more skills, might have given modern humans an edge when conditions turned harsh. "Not a vast edge," Stringer said. "Neanderthals were obvi ously well adapted to a colder climate. But with the superimposition of these extreme changes in climate on the competition with modern humans, I think that made the difference." 54 NATIONAL GEOGRAPHIC * OCTOBER 2008 Which leaves the final, delicate-and, as Jean-Jacques Hublin likes to say, politically incorrect-question that has bedeviled Nean derthal studies since the Out of Africa theory became generally accepted: Was the replacement by modern humans attenuated and peaceful, the Pleistocene version of kissing cousins, or was it relatively swift and hostile? "Most Neanderthals and modern humans probably lived most of their lives without see ing each other," he said, carefully choosing his words. "The way I imagine it is that occasionally S Cut marks on a Neanderthal jawbone, made when flesh was stripped off with a stone tool, testify to an act of cannibalism. All nine skeletons from El Sidr6n show such signs of defleshing. Evidence of cannibalism-to satisfy hunger, or perhaps as a ritual practice-is not uncommon in Neanderthal fossils.