An Evolutionary Explanation For Why Animals Court Their Own Sex

Over 1000 different species throughout the animal kingdom have been observed engaging in same sex sexual behavior, but for the most part, the trait still baffles evolutionary biologists.

Chimpanzees, dolphins, koalas, and even fish such as salmon have all been seen getting it on with members of the same sex, but the practice doesn't seem to yield the same obvious benefits that hetrosexual mating does.

So why do so many animals waste time on something that doesn't seem to increase their fitness?

Some biologists have theorized that the practice may strengthen social relationships in some intelligent animals. Others think that the behavior might either intensify or diminish intrasexual aggression and conflict.

One type of male dung fly for example is thought to mount other males because it denies the male being mounted the opportunity to mate.

A new study published Thursday in BMC Evolutionary Biology by Researchers at Uppsala University in Sweden might provide one of the most intriguing explanations yet.

The researchers hypothesized that since members of the same sex in most species share many of their genes, same sex behavior could occur in males because its underlying genes carry benefits when expressed in females, or vice versa. In other words, while a male who engages in same sex behavior might not get any benefit, his sisters could.

The researchers tested their hypothesis by breeding an animal that in the wild displays a very low level of sexual behavior between members of the same sex. In this case, it was a small seed beetle.

The researchers artificially bred the beetles to create an increase in sexual behavior between members of the same sex, attempting to see if the trait influenced the wellbeing of other members of the population.

What they found is that when they bred males to have sex with other males more, their sisters laid more eggs and produced more offspring than before.

So one of the reasons that so many animals mate with members of their same sex might not be because they themselves benefit, but because the trait benefits the opposite sex in some way, which means it can be preserved through many generations.

For other animals, like many insects, the explanation for why they sometimes mate with the same sex is much simpler: they just can't tell each other apart.