Humans and Other Primates: Learning About Sex among the Sexes

 Frans de Waal has had a long and distinguished career as a primatologist studying the characteristics of species of monkeys and apes.  He has committed recent years to describing what we humans can learn about ourselves from recognizing the similarities and differences with our genetic relatives.  For example, if one wishes to understand what among a human society is based on commonly shared genetic features and what is purely cultural invention, one can conclude a significant genetic involvement when traits are common between us and other primates.  De Waal’s latest book takes on differences between males and females: Different: Gender Through the Eyes of a Primatologist.  We often question the raising of our children and the different characteristics of young boys and girls, worrying that our parenthood is inadvertently imposing traits that might prove harmful to either the children or society.  De Waal addresses that concern by illustrating that all primates, including humans, emerge from the womb with a common set of gender characteristics.  Individual variations from the norm will occur, but there are biologically imposed traits.

“The males’ exuberant boisterousness and displays of vigor explain why young females keep their distance.  It’s not the way they like to play.  This is no doubt why sex segregation marks the play of all primates.  Males generally play with males and females with females.  Their interaction styles are more compatible, and females often retreat from male play initiations.  They do so without any of the gender instruction that takes place in our societies.  In humans, too, sex-segregated play is the rule.  Children all over the world create separate play spheres: one for boys, one for girls.”

De Waal devotes an intriguing chapter to the incidence of same-sex sex in the primate kingdom and compares it to the human species.  He finds some similarities and some differences.

“In all primates, young males seek out males and young females seek out females as playmates, thus creating sex-segregated social spheres that last into adulthood.  These spheres provide great satisfaction and enjoyment, which occasionally spills over into sexuality.  The sharp boundary in human society between the social and sexual domains is artificial.  It’s a cultural invention that, despite moral and religious exhortations, is prone to leakage.”

Perhaps the first observation of animal same-sex sexuality involved penguins about a century ago.  In this species the changing of partners from one gender to the other was so frequent that De Waal considered them to be essentially bisexual.

“There was, of course, a time when we weren’t allowed to reference animal homosexual conduct.  It was too shocking to think about.  That it has occurred in penguins has been known for over a century, though.  The very first report described their behavior as ‘depraved’ and was available only privately, to keep it hidden from a wider audience.”

The penguin experience does suggest a possibly significant difference with humans: there do not appear to be males or females with an exclusive preference for same-sex partners.

“However, it is important to note that so far as we know, there are no ‘gay penguins.’  There is no evidence that these aquatic birds have an exclusive or even dominant orientation to their own sex.”

Homosexual activity is common in primates as well for both males and females

“In 1949 the American ethologist Frank Beach noted that male monkeys regularly mount each other, sometimes achieving anal penetration, while ignoring nearby females…He considered homosexual conduct a basic mammalian pattern.” 

Of the many examples, a notable one involved rhesus monkeys in which the females were more aroused than males during the mating season and expended their excess sexual energy among themselves.

“The rhesus monkey troops that I studied…sex life is arranged so that babies arrive all at once with the first warmth of spring.  To this end, the mating season starts in late September.  That’s when females hang out together and signal that they have sex on their minds.  The males seem to need more time to get ready, but the females warm up for two months of mating by literally jumping on top of each other.”

If evolution produced sexual pleasure to encourage sexual acts and ensure reproduction of species, it apparently saw no reason to restrict that pleasure solely to reproduction.  By 1999, homosexual activity had been documented in 450 different species.  What is intriguing about all this data is that animal species rarely seem to produce individuals that are exclusively homosexual.  Is this an instance where humans display uniqueness?  If so, what is the basis for this uniqueness? 

Understanding homosexuality in humans is critical because many societies have developed an abhorrence towards the practice.  For much of recent history the practice was illegal and many people who considered themselves to be Christians thought it was their duty to punish such people.  Just a few days ago a Christian pastor proclaimed that all homosexuals should be executed.  Those with such attitudes like to believe that homosexuality represents a chosen lifestyle, not a biological imperative.  If one looks at the behavior of other primate species one concludes that homosexual activity is common, but it does not preclude heterosexual behavior in individuals.  To the homophobic this could be interpreted as homosexuality as a lifestyle choice.  Humans exclusively homosexual do not believe choice is involved.  Consequently, there have been efforts to find a biological basis for their behavior.

The neuroscientist Simon LeVay provided a clue.

“Among heterosexuals, a tiny area of the hypothalamus is on average twice as large in men as in women.  Gay men, in contrast, have an area similar in size to that of women.”

Consider the behavior of sheep, in which a finite percent of males seems to be exclusive homosexuals, just as is assumed in humans.

“About one in twelve rams has a strong same-sex sexual preference.  Far from being asexual, these individuals are eager to mount members of their own sex while ignoring nearby ewes.  It is a stable individual trait.  Ovis aries is only the second mammal, after ourselves, in which an exclusive homosexual orientation has been found.”

“As in us, their sexual orientation seems to be reflected in the hypothalamus, which contains a nucleus that is larger in female-oriented rams than in ewes.  In male-oriented rams, on the other hand, its size falls somewhere in-between.”

Is this definitive evidence that homosexual behavior is biologic in origin and is controlled by a tiny speck of brain matter?  The brain is a plastic organ that can modify itself as the demands on it change.  De Waal questions whether it is the brain controlling the behavior or the behavior controlling the brain in this case.  He was surer of a direct connection when a later, more general study was performed.

“It took almost two decades before Ivanka Savic and Per Lindström resolved this conundrum at the Stockholm Brain Institute in Sweden.  Instead of inspecting the same brain area as LeVay, they focused on more general neural traits, such as brain asymmetry, that have no direct relation to particular behavior.  These brain features are fixed at birth and don’t change with experience.  Nevertheless, they reflect gender and sexual orientation.  Brains of gay men are structurally similar to those of heterosexual women, whereas those of lesbian women resemble those of heterosexual men.  Savic concluded that ‘these differences are likely to have been forged in the womb or in early infancy’.” 

These results lead de Waal to the following conclusion.

“In short, even though the brain cannot tell us with certainty what sexual orientation an individual has, it does seem to contain a few markers.  Like gender identity, sexual orientation seems to be present at birth or to develop soon thereafter.  It is therefore part and parcel of who we are.  This applies not only to the LGBTQ community but to all humans (and perhaps also to sheep).  Gender identity in general and sexual orientation in general are inalienable, unalterable aspects of every person.” 

De Waal makes that claim, but then proceeds to question its interpretation.  The way the data was presented seems to imply that there are only two options: either exclusively homosexual or exclusively heterosexual.  This seems to be inconsistent with what we know of human behavior.  Science does tell us that bisexual individuals do exist.  Using his own words.

“The term homosexual didn’t exist until the nineteenth century.  Before that, there was plenty of homosexual conduct but no homosexual identity.  Among men same-sex sex was typically age-structured, with older men penetrating younger ones, such as the soldiers of ancient Greece who boosted their bravery before setting off to war.  During certain eras, sodomy was nearly universal, whereas lesbian relationships stayed mostly under the radar but were probably equally prevalent.  In 1869, Karl-Maria Kertbeny, a German-Hungarian author, coined the twin terms homosexual and heterosexual to replace the pejorative labels that he despised.  Since then, at least in the West, language began to promote a dichotomy that was unknown before.  Homosexual activities used to be supplemental to heterosexual ones, often performed by men and women who at the same time were heterosexually married and had families.  This may still be the case, but it is now obscured by the labeling that we have grown used to.” 

This human perspective would make us look much more like our primate cousins in terms of homosexual activities.  That is not inconsistent with the notion that sexual tendencies are associated with physical properties such as brain function.  Even identical twins can possess differing sexual tendencies.  That suggests the differences were developed in the womb or soon thereafter.  There are so many opportunities for mistakes in cell division to occur that alterations between the once identical specimens is to be expected.  One should expect that in this scenario a continuum of sexual variations would develop—as it seems to happen with other primates.

There is still the question of why homosexual activities seem today to be more likely to involve exclusively homosexual individuals.  It is unlikely that such a dramatic transformation could have taken place biologically in a little more than a century.  Only cultural transformations can develop that quickly.  Perhaps de Waal provides a clue when he points out that other primates do not discriminate against members of their species that have uncommon sexual pursuits, nor do they discriminate against members with differing colorations.  As far as we know, only humans have burdened themselves with organized religions.  Such constructs inevitably discriminate between believers and nonbelievers.  If a religion is successful it will try to force all members of society to live according to its precepts.  If one of those precepts viewed homosexuality as a sin punishable by exile, imprisonment, or death, practitioners would be difficult to find.  Individuals who derive no sexual satisfaction other than from same-sex sex would be the only ones willing to risk the discovery of their practices.  Perhaps our traditional beliefs about homosexuality are merely the fabrications of a highly discriminatory society.