By guest contributor Dr. James Giles

A striking feature of human beings is our lack of a thick coat of body hair. Since all other primates have such fur this suggests the primate ancestors of human beings likewise had fur and that, for some evolutionary reason, lost their body hair. But what could this reason be? There are various theories but none is fully adequate.

In a new attempt to explain this loss of body hair I argue that human hairlessness had its origin in the ancestral mother-infant relationship. In the “naked love theory”, as I call it, this hairlessness is ultimately the result of bipedalism or the ability to walk on two feet. Because of bipedalism, ancestral infants lost the ability to grasp the mother’s fur with their feet, as do other primate infants. They thus could no longer hold onto the mother themselves. Early bipedal mothers therefore had to adapt to the new and difficult task of carrying their infants.

Therefore, infants survived only if mothers had a strong desire to hold them. Because of the pleasure of skin-to-skin contact, the desire to hold the infant would have been stronger in less hair-covered mothers who passed their hairlessness onto their infants. Survival of these infants would have then been greater than that of hair-covered infants.

The hairlessness that began to appear in this context of maternal selection was then reinforced by sexual selection in the male-female sexual relationship. This is because a hairless sexual partner would have enabled the hairless individual to recreate the pleasure of skin-to-skin contact experienced in the mother–infant relationship. Thus, individuals with less body hair were seen to be more sexually attractive than hair-covered individuals. This would have also worked to give hairless individuals a higher chance of leaving more offspring.

One of the benefits of the naked love theory is that, because it explains the origins of hairlessness in terms of the desires for caressing and sex—desires which are fundamental to romantic love—it gives insight into the evolutionary origins of romantic love. This is because the evolution of human naked skin was a precondition for the eventual appearance of romantic love. Comparing aspects of human sexuality with non-human primate sexuality supports this view.

First, although there is a massive involvement of skin-to-skin contact in human sexual intercourse, this is not true for non-human primates. This is simply because the other primates are covered in fur. Consequently, sexual intercourse for them cannot involve skin-to-skin contact in the extensive way that it does for human beings. That is, it cannot involve the caressing of naked arms, abdomen, and thighs, and the rubbing together of naked bodies. Further, when sexual intercourse in our closest primate relatives is compared with human sexual intercourse, not only is it limited in terms of skin-to-skin contact but also in terms of duration. Thus, in the chimpanzee, sexual intercourse lasts for about seven seconds.1 With human beings there is a wide variation. Ten minutes, however, seems to be the average.2

Why then is there this vast difference in the duration of sexual intercourse? The obvious answer, I would argue, is because of the loss of body hair. For it was only with the loss of human hair on the body that sexual intercourse could involve the amount of skin-to-skin contact that it does. Skin-to-skin contact was something that was experienced as highly pleasurable in itself. It therefore became engaged in for its own sake and thus was extended in order to prolong the experience. It is understandable that individuals who engaged in extensive caressing and embracing in sexual intercourse could easily develop persisting attachments to each other. And it is here that we can discern the evolutionary beginnings of human romantic love. For romantic love is an intense attachment to another individual that incorporates sexual desire, a desire that is composed of the more basic desires for mutual baring and caressing. In other words, for me to desire another person sexually I must desire that she be bare or naked for my caress while at the same time desiring that I be naked so that she may caress me. Sexual desire can of course aim at very specific forms of baring and caressing, but these are merely personal expressions of the more basic desire for mutual baring and caressing. The intensity of these physical desires is such that they can easily lead to desires for mutual psychological or emotional vulnerability and care, desires that, according to the vulnerability and care theory of love, lie at the core of romantic love.3

Editor’s note: You can read more about Dr. Giles’ work in his book The Nature of Sexual Desire, or check out an interview with him here.

1De Waal, F. (1995). Bonobo sex and society: The behaviour of a close relative challanges assumptions about male supremacy in human evolution, Scientific American, 272 (3), 82-88.

2Hunt M. (1974). Sexual Behavior in the 1970s. Chicago, Illinois: Playboy Press.

3Giles, J. (2008). The Nature of Sexual Desire. Lanham, Maryland: University Press of America.

Dr. James Giles – Lecturer in the University of Cambridge, Institute for Continuing Education

Ph.D., University of Edinburgh