BBC: Are there any homosexual animals?

Lots of animals engage in homosexual behaviour, but whether they are truly homosexual is another matter entirely

During the winter mating season, competition is fierce for access to female Japanese macaques. But it's not for the reason you might think. Males don't just have to compete with other males for access to females: they have to compete with females too.

That's because in some populations, homosexual behaviour among females is not only common, it's the norm. One female will mount another, then stimulate her genitals by rubbing them against the other female. Some hold onto each other with their limbs using a "double foot clasp mount", while others sit on top of their mates in a sort of jockey-style position, says Paul Vasey of the University of Lethbridge in Alberta, Canada, who has been studying these macaques for over 20 years.

To our eyes these encounters look startlingly intimate. The females stare into each other's eyes while mating, which macaques hardly ever do outside of sexual contexts. The pairings can even last a whole week, mounting hundreds of times. When they're not mating, the females stay close together to sleep and groom, and defend each other from possible rivals.

That many humans are homosexual is well known but we also know the behaviour is extremely common across the animal kingdom, from insects to mammals. So what's really going on? Can these animals actually be called homosexual?

Japanese macaques (Macaca fuscata) mating (Credit: blickwinkel / Alamy)

Animals have been observed engaging in same-sex matings for decades. But for most of that time, the documented cases were largely seen as anomalies or curiosities.

The turning point was Bruce Bagemihl's 1999 book Biological Exuberance, which outlined so many examples, from so many different species, that the topic moved to centre stage. Since then, scientists have studied these behaviours systematically. Full story here!