Since it’s pride month, I thought the evolution of homosexuality warranted some attention. It turns out homosexuality is common throughout the animal kingdom, while homophobia is only seen in one species.
While sexuality is complex and seems to have a lot to do with epigenetics, as well as conditions in the uterus during fetal brain development, this variety is not limited to humans. Instead of thinking of humans as unique and separate from other animals, try to consider that brains, social structure, and cognitive ability exist on a spectrum with humans simply sometimes possessing a “higher degree” of whatever special unique thing we think we have. Such as love and sexuality. Homosexuality is especially common in primates and marine mammals (it’s correlated with intelligence in species). Same-sex relationships amongst animals strengthen social structures and can be particularly useful in systems with a lot of parental care, systems where the females outlive the males (humans?), and systems where not all males get an equal number of mates. Bottlenose dolphins for example are well-known for their bisexual behavior which strengthens social bonds.
When talking about homosexuality in nature, brief periods or episodes of homosexuality are actually pretty common. Male dominance mating (which is very common in giraffes), isn’t really “true homosexuality” because the males do not form any kind of bond, and the males will usually mate with females if they can. Cases of males or females rejecting the opposite sex and forming permanent pair bonds is more rare but absolutely happens.
A classic female-female coupling that actually makes a lot of evolutionary sense from a reproductive point of view, is the Laysan Albatross. The Laysan Albatross is monogamous and mates for life, and almost a third of the parent pairs are both female. This is useful as sometimes males will mate with more than the just their one female mate (basically he cheats on her in the hopes of making more offspring) and as the Albatross has evolved to require high parental care from both parents, female-female parents are actually a necessity in many cases where the father is absent.
Macaques are also rather known for their “lesbianism,” which in this case, has nothing to do with parenting and more to do with them just preferring sex with other female macaques. The males just can’t keep up.
Not all dominant mounting is males
While males mating with other males is very common, scientists have sometimes argued that a lot of that “mating” is simply the males exerting dominance over each other. Females do it to though, especially in the case of the female spotted hyenas who live in a matriarchy. The female hyena is even larger and more terrifying than the male hyena and leads the family.
A study of gay sheep, was actually pretty historical as it really confirmed that there is a biological basis for sexual preference in animals. Sheep do seem to have a much higher rate of homosexuality than other animals where as many as 1 in 10 rams can be gay. Rams have undergone a lot of selective breeding which may provide some evidence that genes are involved in sexual preference. A region in the hypothalamus which is generally much bigger in rams than in ewes was found in gay rams to be the same size as the female’s. The hypothalamic region size variations effected levels of aromatase, an enzyme which converts androgens into estrogens. This supported the theory that hormones present during fetal development plays a role in determining sexual preference.
Bonobos are so closely related to us that it hardly seems worth it to mention them, but they are fascinating none the less. They exist in a peaceful (compared to chimps and humans) matriarchal society where sex occurs between basically every pairing you can imagine, excluding close family members (evolution doesn’t favor inbreeding). If you want to learn more about these super gay cousins of ours, I highly recommend primatologist, Frans de Waal’s books. He’s basically the top authority on bonobo sex. Really the best of the best.
Adoptive gay vulture dads
In what may be one of the cutest stories I’ve read all year, two male griffon vultures from Amsterdam have recently been given the opportunity to raise a chick together. These two males are long-term mates who had been building nests together for months but were unable to produce an egg together (obviously). The zookeepers remarked that it was unfortunate as they were one of the most devoted culture couples observed.
Vultures are monogamous and have biparental care systems, so the males together could still make great parents. When a vulture egg was abandoned, and no heterosexual vultures would agree to incubate it, they gave the egg to the long-term male couple. The males ended up being very enthusiastic helicopter parents, proving that they could successfully hatch an egg even without a female helping. They carefully took turns incubating it, and when it hatched they proved to be protective, loving parents. The fathers have split their jobs equally, taking turns caring for their baby, looking for food, defending the nest, and feeding the baby.
Possibly the most famous gay couple in the animal kingdom is the penguin couple from the central park zoo, Roy and Silo. The two chinstrap penguins, where internationally celebrated for successfully hatching and caring for an egg they were given. Their caretakers noticed that they engaged in mating behaviors with one another and seemed to instinctually want an egg of their own, once seeming to try and hatch a rock that resembled an egg. Other gay penguin couples have been observed actually trying to steal eggs from other penguins, a behavior that’s not uncommon in heterosexual penguins either. Penguins typically engage in multiple long term relationships (kind of like humans do), and interestingly, many of them will switch around between male and female partners in their lifetime.
Oregon Health & Science University. “Biology Behind Homosexuality In Sheep, Study Confirms.” ScienceDaily. ScienceDaily, 9 March 2004.
Our Inner Ape, Frans de Waal