26th Annual Meeting of the International Academy of Sex Research

Lorraine Dennerstein, AO, MBBS, PhD, FRANZCP, DPM

Disclosures

July 10, 2000

In This Article

Evolutionary Aspects of Human Sexual Response

Evolutionary factors affecting the human male sexual response and mating were presented separately by Professor Alan Dixson, a zoologist, and Professor Stephen Gangestad, an evolutionary psychologist. Professor Dixson, currently the Director of the Center for Reproduction of Endangered Species, Zoological Society of San Diego, California, is the author of the most complete study of comparative anatomy of the genitalia of primates.[12] This comprehensive study enables us to understand how sexual behavior and the anatomy of the genitalia of the human male may have evolved.

Some interesting findings were that those species with the greatest testicular size/body weight were those who live in multimale/multifemale societies where females have sex with many different males and sperm competition is an issue. The human male did not have the testicular size/body weight suggestive of this pattern, but rather has moderate-sized testicles suggestive of those primate species that live in monogamous or polygynous relationships. The longer refractory period in the human male is also indicative of monogamous societies.

The human male was also not remarkable for length of the penis. The longest penile size occurs in multimale/multifemale societies where sperm competition exists. Females of the Bonobo species have a sexual swelling when fertile, as a visual signal to the male. The swelling is large and increases the depth of the vagina by up to 50%. The Bonobo male must have a very long penis to deposit a copulatory plug at the cervix.

Other findings of relevance to human sexual interaction were that women rate the mesomorph as the most attractive body shape cross-culturally, and attractiveness is increased by the presence of chest and body hair. Of note is that same-sex interactions are observed in subhuman primates, but these are social behaviors related to greetings, dominance, and other social behaviors. Same-sex behaviors do not become erotic preferences as they do in humans.

Professor Gangestad presented evidence about factors that may indicate an attractiveness of certain males to females for extra-pair or short-term sexual relationships.[13] These features include the presence of structural symmetry in appearance, which make some men more attractive and may indicate underlying genetic fitness, which, in turn, may confer genetic benefits to offspring. Symmetry was found to covary with other traits conferring evolutionary advantage (such as aggression and intellectual ability). They observed that women found the smell of more symmetrical men more appealing during the fertile time of the menstrual cycle, indicating olfactory mechanisms may play a role.

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