Sexuality

Human Evolution and Sexuality

While all mammals, including humans, reproduce sexually, humans exhibit different patterns of sexuality than other members of this class of animals. Even among the primates—the order in which humans are categorized in the Linnaean taxonomic system and that includes apes and monkeys—humans are distinct when it comes to patterns of sexuality.

These differences are considered by anthropologists and other scientists as being representative of adaptive strategies, or coping mechanisms, that humans have adopted over time in response to environmental, biological, and social pressures. While some scholars focus on these pressures individually, the discipline of anthropology generally acknowledges that they are likely to be interconnected. In other words, there may not be one individual source for the uniqueness of human sexuality.

In contrast to many other mammals, for example, human females are sexually receptive throughout the year, regardless of whether or not they are fertile. This characteristic is related to the loss of estrus among human females. That is, at some point in their evolutionary history, human females gained the physical capacity to conceal ovulation. The period of time during which females are fertile became unknown to males and, in most cases, to females themselves. The process whereby females gained concealed ovulation may be linked to other physical changes that occurred through evolution such as the ability to walk upright and the loss of body hair.

As a byproduct of this change, humans mate throughout the year and sexuality has implications that range further than its reproductive function. The social impact of this trait touches on marriage, family structure, economic structure, and so forth. A related [Page 2077]trait, for instance, and another distinction between humans and many other mammals, is that humans demonstrate a tendency for pair bonding, where a male and a female collaborate in the raising of offspring.

What is the adaptive advantage of these interrelated traits? One answer may be that since humans have a longer gestational period and offspring have a longer maturation period than those of other mammals, collaborative parenting may lead to a higher success rate in the raising of young. Human babies are born defenseless and unable to survive on their own. Parents must therefore feed and shelter their young for a longer period of time. The capacity for year-round mating may be one factor that facilitates the maintenance of these pair bonds since the male and the female mate repeatedly, even during times where there is no possibility for reproduction.

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