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New research has discovered that female gorillas can form homosexual relationships.

Pink News reports Associate Professor Cyril Grueter observed the behavior of mountain gorillas in Rwanda and found female gorillas get sexual pleasure from other females. This is the first documented example of same-sex relationships in female mountain gorillas, according to Pink News.

Grueter’s research found that 18 out of 22 gorillas engaged in homosexual behavior including frottage and “courtship displays” similar to heterosexual acts between gorillas. Grueter says female gorillas “can shift from homosexual to heterosexual sex” in the same way human women can. While some male gorillas that were observed tried to interrupt the sex acts, others remained neutral.

“Given that all these observations come from wild groups, not gorillas held in captivity, it is obvious that homosexual activity is part of the gorillas’ natural behavioral,” Grueter told Pink News.

Grueter believes some female gorillas participate in sex acts with other females after facing male rejection. He says another factor might be to prevent other females from having heterosexual sex to decrease their “reproductive success.”