The Human Evolution Blog

It is not uncommon among social mammals to engage in division of labor between the sexes. Female lions do all of the hunting; males loaf around and occasionally fight other males. Chimpanzees have a strictly male-dominated social hierarchy, while bonobos employ a matriarchal structure in which dominance is enforced by females. These sex roles can play out in all aspects of life, from child-rearing to hunting to the dynamics of courtship and mate selection.

It has long been wondered how ancient humans fit into this mix. On the one hand, human males are larger than human females, on average. In animals, average difference in body size between the sexes is strong evidence of different behaviors for the sexes. For example, male gorillas, called silverbacks, are nearly twice the size as females, a trait that is important for defending a harem from other males.

However, the average size difference between the sexes in humans is relatively modest, 10-15%, with a wide range for each, meaning tons of overlap. Further, the size differences among the human sexes seems to have been larger as we look through our evolutionary past. In other words, the difference has been diminishing and is very nearly gone, meaning that we could have been evolving away from whatever gender roles our ancestors had.

Another way that anthropologists attempt to ascertain division of labor among the human sexes in the distant past is to study contemporary hunter-gatherer populations of humans. The reasoning is that isolated tribes of pre-agricultral societies probably live their lives in a way that more closely resembles the “ancestral environment” that shaped human evolution for millions of years. There are many limitations with this approach, but it has no doubt provided insight into how prehistoric societies developed into modern ones.

The study of pre-agricultural societies has provided little in the way of consistent gender roles, save one. Adult women most often work together to cooperatively nurse and care for young children. In most cases, these women also perform other functions related to hearth and home, such as the fabrication of clothing, utensils, and even the dwellings themselves. Men, meanwhile, often spend extended periods away from the settlement hunting or fishing in roaming bands. As a result, women often engage a richer toolkit of skills, while men are more focused. This generalization is rife with exceptions, of course.

The tasks performed by each sex vary widely among societies based on the available material for toolmaking, local flora and fauna, etc. Both sexes frequently fashion and use tools, transmit cultural knowledge and skills, and are stratified by social status, which includes elaborate culture-specific means for conflict resolution. While many “primitive” human cultures are patriarchal, there are also some matriarchal societies, and the vast majority are largely egalitarian, with positions of status that provide very little privlege.

What about extinct hominid species?

A new study on Neanderthal teeth has raised the possibility that a sexual division of labor may have been present in some Neanderthal societies. This conclusion is supported by the fact that there are characteristic wear-and-tear markings on their teeth and that these markings are different between males and females.

Wear markings on teeth are common in the remains of hominids because the teeth were used extensively in a variety of daily tasks. We see this in extant primates as well, as the mouth becomes almost like a third hand, holding things, breaking things, etc. The use of the mouth for tactile manipulation exploded in hominids with the advent of tool use, fashioning of clothing, construction of shelter, and so on. The teeth of recovered adult hominids show the telltale signs of repetitive, task-oriented wear.

Not surprisingly, the marks on the teeth of early Homo sapiens, as well as those of contemporary pre-agrarian humans, show sex-based differences. In some cases, the precise reason – that is, the task that leads to the marking patterns – is known. In either case, a sex-based division of labor has led to different marking patterns on the teeth of women than those of men.

Until recently, no one had ever thought to look if the markings on Neanderthal teeth were different between men and women. When researchers in Spain did this using 99 teeth recovered from 19 different Neanderthals recovered from four different locations, the results were striking.

Both male and female Neanderthal teeth showed two types of antemortem wear: striations (stripes) and chipping. The striations mostly came about through repetitive, task-oriented work such as holding or pulling skins, thread, or other utensils with the mouth. The chipping, however, is likely the result of trauma, either by biting something too hard, or by failure of the tooth while performing some function.

Both males and females had striations on the labial (front) side of their front teeth, but the striations were consistently longer in women. This doesn’t indicate that they used their teeth for some task more than the men did (that would cause deeper grooves, not longer ones), but that they used them for a different task.

Although both males and females showed dental chipping, they did so on different teeth. The males typically had chips on their top teeth, while women had chips on their bottom teeth. Statistical analysis revealed that the odds are tiny that these differences are due to random sampling error.

While we can only speculate what tasks caused these different kinds of teeth marks, the sex differences are telling. This indicates that a sex-based division of labor likely existed in Neanderthal culture. Because Neanderthals show slightly greater difference in body size than humans do, it is not altogether surprising that the two sexes had different social roles in their communities. What is new and interesting about this result, is that the sex-differences were cultural, that is, they were learned skills passed on from generation to generation through instruction.

Although simple aspects of culture have been documented in a growing list of other species, it is indisputable that the phenomenon of culture exploded with Homo sapiens over the last 50,000 years. We now know that other hominid species were well on their way toward establishing rich cultures of their own. The discovery of a sex-based division of labor in Neanderthals furthers that point.

The various tasks that the Neanderthal men and women performed must have been somewhat similar despite being separated by thousands of kilometers and thousands of years. We know this because the tooth wear patterns were strikingly consistent across several Neanderthal sites. Because it is exceedingly unlikely that the tool-making or tool-using behaviors that left these dental marks were genetically programmed in these Neanderthals, the likely explanation is that they represent a stable cultural behavior that was passed on from generation to the generation among the men and women respectively.

This is yet one more example that the Neanderthals lived in socially rich communities, not unlike the Homo sapiens communities that would eventually emerge from Africa and overtake them.

-NHL    (@nathanlents)