If you didn't know much about monkeys, you probably wouldn't know there is a species of ape called the bonobo, which is a close relative of the chimpanzee. Even if you knew a lot about monkeys, you probably wouldn't know that bonobos are one of the leading species for lesbian animal research.
Recently, researches have added bonobos to the long list of over 1,500 species that exhibit homosexual behavior. "Female bonobos rub one another's genitals so often that some scientists have suggested that their genitalia evolved to facilitate this activity (Scientific American)." So why do these monkeys have frontal clitorises? Because it helps facilitate lesbian sex. Why do these monkeys have lesbian sex? That is another story.
Lesbian sex helps ease social tensions and promote social cohesion within the bonobo species. Bonobos live together in groups of about 60 in a matriarchal system. During adolescence, females leave the group and join other clans of bonobos. In order to gain admission to a new clan, the young monkey bonds with other female through grooming and sexual encounters. This also ensures protection from harm and access to food.
Lesbian sex is also part of a "general pecekeeping strategy" in bonono society. Frans de Waal, a primatologist studying to bononos, observed, "when one female has hit a juvenile and the juvenile's mother has to come its defense, the problem may be resolved by intense GG-rubbing between the two adults."
There is another story of two male penguins in the Central Park Zoo who exhibited gay behavior. These penguins, named Roy and Silo, mated, built a nest, and brought a rock into the nest in an attempt to mimic incubating an egg. One of the zookeepers took an actual egg from a pair of straight penguins who were having trouble hatching it and placed it in Roy and Silo's nest. After 34 days, a female chick was born and raised by these gay penguins. By the way, the chick turned out to be a lesbian.