Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live (5 page)

What’s more, anthropologists increasingly doubt that any of the modern hunter-gatherer societies are truly “pristine,” living the way that even their own ancestors did just a few centuries ago. The San, for instance, trade with their farming neighbors, and in fact may themselves have farmed sometime in the recent past. The Inuit are now known to have had complex networks of trade that, as anthropologist Rosemary Joyce of UC Berkeley says, “reached into Russia long before ethnographers came to describe their supposed simplicity.”
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In the 1970s, a tribe of hunter-gatherers called the Tasaday was supposedly discovered to be living as “remarkably peaceful remnants of Stone Age life,” according to a
Science News
report by Bruce Bower.
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But further investigation cast doubt on the authenticity of the Tasaday’s isolation, and it now appears that at least part of the people’s lifestyle, including their use of stone tools, was faked to attract media attention.

Many other contemporary foraging peoples are living in marginal environments far from their ancestral homes, pushed to the places where more technologically advanced people do not want to live. Or, like the Yanomami and other people living in the Amazon rain forest, they may be the remnants of much larger, and possibly quite different, populations that were decimated by Western diseases brought by the early European explorers. The Lacandon of Central America were once held up as a model of what “primitive” life would have been like if people had not begun to farm; we now know that they were pushed to the edges of the Spanish colony in the sixteenth century, adapting to their new environment by taking on behaviors like hunting and trading.

It isn’t that one can’t learn anything from these people—far from it, as they can often provide novel testing grounds for hypotheses developed in Western societies with different economies and cultures. Studying a diversity of cultures is the best way to understand when our generalizations are truly universal and when they inadvertently reflect biases from our own backgrounds. But the contemporary foragers do not mirror our past, and if they show admirable attributes, such as the absence of diseases like diabetes, or a lack of anxiety over unemployment, we cannot conclude that our ancestors were similarly blessed and that we have gone astray as we have taken on a settled existence in the course of evolution. As Joyce puts it, “We can still use the modern hunter gatherers to explore how small scale human societies work, but we have to see them as examples of small scale, not of earlier stages of evolution.”
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The Neandertal makeover

Anthropologist John Hawks, who maintains a popular blog about human origins,
²³
has a set of entries called the “Neandertal anti-defamation files.”
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According to the old conventional wisdom, Neandertals were those brutish hairy characters that lost out in evolution to the more cunning and—not coincidentally—more attractive
Homo sapiens
, who went on to make better tools, develop language, and generally evolve into, well, us. But ever since the 2008 finding of complex stone tools made by Neandertals, and more particularly since the 2010 discovery by Svante Pääbo and his colleagues that 1–4 percent of the genome of non-Africans today seems to have come from Neandertals, all parties have been hastily revising their stories.

Neandertals are suddenly cool;
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they had bigger brains, and possibly more sex, than previously thought, at least according to the popular press. The
Guardian
newspaper sympathetically provided the headline “Neanderthals: Not Stupid, Just Different.”
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Wired.com huffed, “Neanderthals Not Dumb, but Made Dull Gadgets.”
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Scotsman.com was blunter: “Stone Me—He’s Smart, He’s Tough and He’s Equal to any Homo sapiens.”
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At the new Neanderthal Museum in Krapina, Croatia, the displays even intimate that the Neandertals brushed their teeth. (Perhaps more disturbingly, or at least oddly, the former rocker Ozzy Osbourne attributes his survival of past excesses, such as drinking “up to four bottles of Cognac a day,” according to the
Daily Mail
, to having Neandertal genes, a discovery he purportedly made with the help of a private genetics company.
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)

Since the Neandertals themselves, along with other now-extinct forms of humans in our direct lineage, are no longer around to tell us what they were like, we have to use what they left behind, in the form of tools, the remains of the animals they ate, and their own bodies, to understand the lives of our ancestors. How much can we conclude from these traces of bone and rock, and what do they tell us about where we came from?

Even just a fragment of skull can provide enormous amounts of information about the brain and body it was once part of. Any fan of the television show
CSI
knows that approximate age, height, and sex can be extrapolated from part of a skeleton, but modern anthropologists can easily outdo such fiction in their detective abilities. For example, the Neandertal brain, while about as large as that of a modern-day human, is shaped differently: it is more elongated and lacks the front bulge apparent in humans. Researchers at the Max Planck Institute for Evolutionary Anthropology in Germany closely examined the skulls of a Neandertal newborn baby and one older infant. The younger skull had a somewhat elongated braincase, like that of a human newborn, but the older Neandertal baby skull had not begun rounding in the areas at the top and base—the feature that gives human skulls their distinctive appearance. The researchers concluded that the Neandertals, even with their big brains, had a different trajectory of brain development than modern humans have, which could mean that our unique capabilities are a product of very early developmental processes.
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In other words, it’s not just the parts you have, but how they came to be, that determines your behavior. Other scientists are not convinced, given the scanty set of bones used for analysis, but regardless of the claim itself, the studies point to the amazingly detailed reconstructions that can be made using just a few bits of bone.

Teeth have long been used to draw inferences about diet, but recent developments in the analysis of dental enamel itself are providing an exciting new way to determine what our ancestors’ diets were like. It’s a rather more benign version of the idea that, when you have sex, you’re also having sex with all of your partner’s previous partners. When it comes to food, your teeth reflect not only the types of plants you eat, but the plants that the animals you eat ate themselves. Different kinds of plants use different kinds of carbon in their transformation of sunlight into energy, and those carbon variants can be tracked in the tooth enamel of animals, with trees and shrubs having a different chemical signature than grasses and sedges have. Anthropologists Matt Sponheimer and Julia Lee-Thorp examined the teeth of
Australopithecus africanus
and found evidence of appreciable amounts of the grass and sedge type of carbon, suggesting that these hominins ate seeds, roots, and tubers, and also could have eaten grazing animals.
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They did not necessarily hunt big game; scavenging or eating insects like beetle larvae could have had the same result. Nonetheless, the study illustrates how much data can be gleaned from indirect sources.

What about reconstructing not brain growth or other aspects of anatomical evolution, but ancestral behavior? Here, too, fossils have played a role, but the extrapolation is a bit riskier.

“Neanderthals Really Were Sex-Obsessed Thugs,” blared a 2010 headline from the UK newspaper the
Telegraph
,
³²
and others were quick to follow, with AFP cheerfully noting, “Neanderthals Had a Naughty Sex Life, Unusual Study Suggests.”
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Neandertals were not the only subject of the study in question, but as I mentioned already, they seem to be undergoing such an image transformation that the usage was apparently irresistible. The supposedly salacious news comes from another examination of fossil fragments, finger bones this time, taken from Neandertals, four species of ancient hominoids, some early but anatomically modern humans, and data from four kinds of modern apes, including gibbons. The authors, led by Emma Nelson of the University of Liverpool, were interested in the kind of mating system our ancestors and their relatives might have had.
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Did males compete with each other to gain access to multiple females, or were the species monogamous? Overall difference between male and female body size is often an indicator of the degree of multiple sex partners in a species, since selection for more competitive males often means that those males are heftier and hence better fighters. The more extreme the difference between the sexes, the more exaggerated the mating system. Male elephant seals, for example, are two to three times the size of females, and mating success in this species can be extraordinarily skewed, with a single bull in one population siring over 90 percent of the pups and the majority of the losers having no offspring at all.

Gauging overall body size difference between males and females can be tricky, however, if all you have are a few skeletal bones from each sex. What if you happened to measure an exceptionally large female or exceptionally small male? The finger bones were used because the ratio between the index (second) finger and the ring (fourth) finger is believed to reflect the levels of male sex hormones that an individual was exposed to while in the womb. In men, the second digit tends to be shorter than the fourth; in women, either the two fingers are more or less the same size or the second is slightly longer than the fourth. Lower ratios thus could indicate higher levels of male sex hormones, which might be expected in a species with greater male competition and less long-term pair-bonding.

Over the last decade or so, this ratio between the lengths of the digits has attracted attention from evolutionary psychologists, who purportedly found that sexual orientation, musical ability, female fertility, and several other characteristics were reflected in differences in the finger ratios of the subjects.
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Nelson and her colleagues went a step further: instead of looking at the ratios within a population, they compared digit ratios among all of their specimens. We already know that gorillas, chimpanzees, and orangutans have multiple sex partners in a breeding season, whereas gibbons are relatively monogamous. Of the fossil species, all but
Australopithecus afarensis
—Lucy’s species—had digit ratios suggesting that they were more like the gorillas or chimps and less like the gibbons, and the Neandertals were considerably more like those somewhat promiscuous species than are modern humans. Hence, presumably, the headlines about Neandertal “randiness,” as the UK
Mirror
put it.
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Can we conclude, then, that the majority of our ancestors and their relatives, including the Neandertals, had a mating system in which men were able to have multiple wives, and that our monogamy is therefore a recent innovation? Maybe not.
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Nelson and her fellow researchers were quite cautious, noting that their sample of bones was tiny, and that if the results were corroborated by, say, additional data on body size differences between the sexes, “digit ratios represent a supplementary approach for elucidating the social systems of fossil hominins.”
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The use of digit ratios has been controversial almost from the start, with some researchers, including Luká
š
Kratochvíl and Jaroslav Flegr of the Czech Republic, suggesting that the difference is a statistical artifact arising from the simple fact that men have larger fingers than women.
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We also know virtually nothing about how to interpret the numbers themselves; the single anatomically modern fossil human, thought to be about 95,000 years old, had a ratio of 0.935, compared with the contemporary value of 0.957. The gibbons measured 1.009; the chimpanzees, 0.901. So if we are 0.052 units away from our monogamous relatives, but 0.056 units from our promiscuous ones, what does that make us? The answer is that we have no idea. John Hawks is skeptical about using the ratios to predict mating systems, partly because hands in apes and perhaps ancient humans are or were used in different ways, including locomotion, and hence are subject to different types of natural selection.
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I do not mean to argue that we should throw up our hands—whatever their digit ratios—in defeat and give up on the prospect of deducing anything about the ancestral human lifestyle from fossils. But the fossils themselves are often so limited, and the links between steps of logic based on so many assumptions (does prenatal hormone level always mean greater male competitiveness? do infant brain differences reliably translate into adult behavior?) that creating a clear picture of our past from our remains is not a straightforward proposition.

How chimpy are we?

No other species of the genus
Homo
are alive today, which means that if we want to use living animals to learn about what our ancestors must have been like, we have to look to somewhat more distant relatives. The resemblance between humans and the great apes, such as chimpanzees, has not escaped people’s notice ever since those other primates were discovered, and it fostered the erroneous idea that we are literally descended from modern monkeys. The truth, of course, is that we and the monkeys and apes arose from the same ancestor, with humans splitting from the apes approximately 5–7 million years ago. That is still quite recent, which means that the traits we see in chimps, such as tool use, group hunting, or violent conflict between social units, can look like the remnants of our own heritage, and they have sometimes been seen as such.

Richard Wrangham and David Pilbeam titled a book chapter “African Apes as Time Machines,”
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and Wrangham generally makes the case for humans exhibiting more “chimpiness” than similarity to any of the other great ape species.
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Some of that chimpiness has to do with the apes’ propensity for male dominance and violence—a propensity not shared by our other closest relative, the bonobo. Bonobos have more egalitarian societies in which social tension is resolved by sex, which occurs between members of the same sex as well as between males and females.