Sex, Reproduction, and Scenarios of Human Evolution

This is a short essay by Claudine Cohen in Rethinking Human Evolution, edited by Jeffrey H. Schwartz, which is part of a series in theoretical biology. I will probably read several of the essays and comment separately on each one. I am attempting to update myself in a field that I find interesting.

In The Descent of Man, Charles Darwin speculated that in early human history mate selection was performed by females, based on the physical and social characteristics of males, and that these choices affected the characteristics of males over time. This is the same idea that I mentioned a few years ago, regarding speculation that Dutch men are the tallest in the world because Dutch women selected them, considering tall men better providers than short men. However, Darwin thought that mate selection later became a male behavior, and that women began to adorn themselves so as to make themselves more attractive to men. While Darwin admitted that sociocultural practices can affect mate selection, he thought that, after the early period, males generally tended to dominate women.

From the 1920's to the 1970's, cultural anthropologists rejected biological evolutionary models in favor of human social structures. In the mid-1970's sociobiology was popularized by E.O. Wilson and gene-maximization was popularized by Richard Dawkins. I think that Cohen may conflate Wilson's views with those of Dawkins, because they are not identical. She thinks that Dawkins's support of gene-maximization is reductionistic and provides an unsubstantiated advantage to males. Wilson's views are more concerned with group or multi-level selection, which are different things entirely. In any case, Cohen favors maintaining the importance of socio-cultural factors in human sexual behavior and she seems to dislike genetic explanations of this subject. When she wrote this essay (in about 2016), other deterministic models, such as Robert Sapolsky's, were not well known. I think that the clunky old cause-effect model of determinism, especially through genes, is giving way to a messier model such as Sapolsky's. Under that model, specific behaviors of humans do emerge causally, but we can barely comprehend how. Different sexual behavior does emerge from different social contexts, but those contexts also fit within broader deterministic models. While Cohen does seem to approve of Darwin's views, she does not focus on the central Darwinian idea that species go extinct for a wide variety of reasons: if a species goes extinct as a result of its social practices, it lacks fitness, according to Darwin, and social causes may be just as causal as the earth being struck by a large asteroid. I think that many people, even in the sciences, inject free will into their theories because it provides the feeling that we have control over our destinies – even though we don't. 

I found Cohen a bit more enlightening in other areas. The fact of concealed ovulation in humans, but not in other primates, had been a puzzle to me. Was it to conceal paternity? There is a convincingly simple hypothetical explanation for this: bipedal gate. The genital exposure of female humans is much less conspicuous than that of other primates, not attracting as much attention. So it is quite conceivable that, with the gradual development of other erogenous zones in the female body, the role of sexual signaling from the vulva gradually declined. The increasing complexity of human social structures, including the use of clothing, may also have reduced the desirability of conspicuous estrus:

In the absence of visible estrus, human sexual behavior and reproduction become disconnected (Godelier, 2004). Consequently, the uniquely human manifestations of eroticism and sexual pleasure (see Bataille 1957, 1961), coexist with, and may even replace, the physiological function of procreation (Zwang 2002).

More generally:

The acquisition of concealed ovulation has been viewed as a key event leading to the transformation of gender relationships and roles in human groups. If it was related to the acquisition of Hominin bipedal gait, its roots lie well before the origin of the genus Homo. Understanding concealed ovulation – its origin, causes, and effects – is likely fundamental to understanding human evolution and the emergence of social structure, as is reflected in its being the starting point of several scenarios of "hominization."

Another interesting area that Cohen delves into is the social and other effects of the demands of raising human babies. The workload is so high that a male partner is generally needed to at least provide food. But cooperation spills over into the surrounding group, leading to general cooperation within that group. More interestingly, humans are the only primates with menopause, and other female primates remain fertile up to their deaths. 

Whereas young female apes leave their mothers to join their male partners' territories (patrilocality), the positive role of grandmothers is favored by matrilocality, that is, the cohabitation of daughters with mothers (in contrast to cohabitation of the son's mother and his wife). In turn, this leads to a close and harmonious distribution of roles for caring and educating children. In humans, matrilocality permits a better environment for raising young children. Older women, freed of reproductive constraints, can achieve the status of a wise and dominant figure, and contribute to the welfare of their group, by virtue of the knowledge and experience they acquired over a long period of time, one that extends well beyond the cessation of fertility.

In this vein, Cohen suggests that figurines such as the Venus of Willendorf (28,000-25,000 BCE) are not symbols of fertility, but represent the importance of postmenopausal women in those societies.