Wednesday, October 04, 2023

Homosexuality Evolved in Many Mammals to Promote Social Bonding and Mitigate Conflict

I have argued that homosexuality is biologically natural, and that that supports the liberty of homosexuals as a natural right, including the legal right to same-sex marriage (as upheld in Obergefell v. Hodges).

Now, we have a new study of the evolution of same-sex sexual behavior in mammals.  Carl Zimmer has a good article in the New York Times on this article.

Jose Gomez and his colleagues surveyed 6,649 species of living mammals that first arose about 250 million years ago.  They saw that same-sex sexual behavior had been reported for 261 mammalian species (about 4% of the species).  Same-sex sexual behavior included mounting and/or genital contact (87% of the species), courtship (27% of the species), and pair-bonding (24% of the species).

They found that same-sex sexual behavior was associated with shifts from solitary living to sociality and with intrasexual aggression (particularly among males).  This suggested that same-sex sexual behavior had evolved to establish, maintain, and strengthen social relationships and to mitigate aggression and conflicts.

It is not clear, however, whether they see this as explaining the evolution of human homosexuality.  Gomez told Zimmer that their study could not explain sexual orientation in humans.  He said: "The type of same-sex sexual behavior we have used in our analysis is so different from that observed in humans that our study is unable to provide an explanation for its expression today."  But what they say about this in their article is confusing:

"Same-sex sexual behavior is operationally defined here as any temporary sexual contact between members of the same sex.  This behavior should be distinguished from homosexuality as a more permanent same sex preference, as found in humans.  For this reason, our findings cannot be used to infer the evolution of sexual orientation, identity, and preference or the prevalence of homosexuality as categories of sexual beings.  Nevertheless, even taking into account this cautionary note, by using phylogenetic inference, our study may provide a potential explanation of the evolutionary history of the occurrence of same-sex sexual behavior in humans" (7).

This looks like a strange contradiction.  In the first three sentences, they deny that they can explain the evolution of homosexuality in humans.  But in the last sentence, they say their study "may provide a potential explanation of the evolutionary history" of human homosexuality.  Apparently, they think that while "homosexuality as a more permanent same sex preference" is uniquely human, this human propensity to homosexuality might be rooted in the evolved inclination of some other mammalian species for "temporary sexual contact between members of the same sex."

If we knew that a same-sex human couple were engaging in courtship, mounting, genital contact, and pair bonding, surely that would be enough to identify them as homosexual.


Empedocles said...

The fact that homosexuality is found in other species means nothing in establishing its biological function since every kind of defect, deformity , or disease, such as cancer, is found in multiple species. See The Myth Of Sexual Orientation (, or Normal Sexuality (, or Homosexuality Proves the Existence of God (

Larry Arnhart said...

Homosexuality serves biological functions such as social bonding. Cancer does not serve such functions.

Empedocles said...

So in heterosexuals the biological function of sexual attraction to to bring male and female together to produce offspring, but in homosexuals the purpose of sexual attraction is social bonding? Is there any other evolved human feature that is like this where for some people an item has one function but in other people it has another? Is the heart for pumping blood in some people but for something else in other people? Is the eye lens for focusing light on the retina in some people and for something else in other people? Is sexual attraction the only item that is like this? Why is sexual attraction uniquely immune to the principle that all humans have the same biological functions? Does sexual attraction ever malfunction or is it uniquely infallible whereas all other biological features are subject to defect or deformity? If homosexuality is not a case of sexual attraction not functioning as designed what is?

Larry Arnhart said...

The evolution of sexual receptivity across the menstrual cycle and not just during ovulation in bonobo and human females suggests that reproduction is not the only evolved function of sex

Roger Sweeny said...

Many characteristics seem to have more than one function and some seem to have no direct function. So for the latter, male nipples (and for many in later life, what are somewhat humorously called "man boobs"). The "function" of male nipples seems to be simply that it is easier to create human bodies where both XX and XY have nipples but only XY grow bigger and become capable of lactation at puberty. "Man boobs" are a byproduct of the human ability to store energy as fat and perhaps a shared male/female propensity to store it behind the nipples.

The human brain has many, many functions. To think and feel in certain ways. To tell lies and to detect lies. To perceive the world in color and 3-D. All sorts of conscious and semi-conscious stuff. But it also does things that we are largely unaware of, and usually have no control over. It makes the heart beat makes the lungs breath in and out.