Male Japanese macaques compete fiercely during the winter mating season, with other males - and females.
Paul Vasey of the University of Lethbridge in Alberta, Canada has been studying Japanese macaques for 20 years and he has noticed that homosexual behavior between female macaques is normal behavior, according to the BBC. Not only do the females engage in genital stimulation, they also spend time together, groom each other and defend each other from rivals.
If the argument is that heterosexuality is beneficial for evolution, because of the need to reproduce offspring, what place does homosexuality have in the wild?
A book titled "Biological Exuberance" written in 1999 by Bruce Bagemihl identified examples from various species demonstrating that homosexual behavior in animals is more common than previously believed.
Still: What would Darwin say about the Japanese macaques?
"So many females of the group are engaging in this behavior and there are males sitting around twiddling their thumbs," Vasey told BBC. "There's got to be a reason for this. There is no way the behavior can be evolutionarily irrelevant."
In 2006, Vasey and his team suggested that the females were able to use different methods of genital stimulation, so the females were just seeking sexual satisfaction."She can do so in a homosexual context just as easily as in a heterosexual context, so the behavior spills over," Vasey told BBC.
Vasey also said that the Japanese macaques are not homosexual. Female might mount other females, but they mount males as well, most likely to encourage more frequent mating.
Male flour beetles are reproductive ninjas, according to BBC. When a male flour beetle mounts another, he deposits sperm. The male carrying the sperm will unwittingly transfer the sperm to a female the next time he mates, so the male who deposited the sperm gets to reproduce without the hassle of courtship.
The Hawaiian Laysan albatross does seem to engage in lifelong homosexual relationships, according to the BBC. The Laysan albatross pairs up for life and successful chick rearing takes two. Researchers found that in one Laysan albatross community on Oahu, 31 percent of the parenting pairs are female-female. The same-sex partnerships rear chicks, usually fathered by a male cheating on his lifelong mate.
According to BBC, LeVay proposed that the gene responsible for homosexuality in males could also make females more fertile or more desiring of mating and that the siblings of homosexual sheep could produce more offspring than other sheep. "If these genes are having such a beneficial effect in females, they outweigh the effect in males and then the gene is going to persist," said LeVay, according to BBC.
Still, LeVay and Vasey believe that the only wild animals to have cases of true homosexuality are humans, according to BBC. "It is not the case that you have lesbian bonobos or gay male bonobos," Vasey told BBC. "What's been described is that many animals are happy to engage in sex with partners of either sex."
Darwin did notice that animals have more offspring than they need. A couple only needs to have two children to replace themselves on the Earth, but in reality, he noticed more offspring than they need in order to guarantee survival (some of the young will die in the wild before they can reproduce).
Now, sexual behavior has gone from solely reproduction to reproduction and pleasure. "Homosexual behavior doesn't challenge Darwin's ideas," said Marlene Zuk, from the University of Minnesota, according to BBC. Shifts in sexuality demonstrate the flexibility that evolution allows.
