Homosexual behavior is much more common across the animal kingdom than we first thought, new research has found.
Scientists found that 78 percent of animal behavior experts had seen some degree of same-sex sexual behavior in animals during their research, according to a study published in the journal PLOS ONE.
Previous research has established that homosexuality has been observed in over 1,500 species of animals from all walks of life, ranging from tiny insects to other primates.
"Same-sex sexual behaviour (SSSB) occurs in most animal clades and is defined as the act of engaging in sexual behaviours, such as mounting, intromission, and genital-oral or manual-genital contact with members of the same sex," the researchers wrote in the new paper.
"SSSB has been a focus of study in some primate and ungulate species (e.g., in deer (Cervus spp.); American bison (Bison bison); Japanese macaques (Macaca fuscata)) yet has remained a low research priority in the field of evolutionary biology."
In the paper, the researchers describe how they surveyed 65 animal behavior experts who had observed animals in the field, asking if they had seen any homosexual behavior in the species they were studying. They found that there were 58 reports of same-sex sexual behavior across 42 of the 54 individual species identified, amounting to 77.8 percent.
"Species identified as engaging in SSSB by survey respondents were compared with existing literature on SSSB in mammals. Of the 44 unique species identified as engaging in SSSB in the survey, 17 (38.6 percent) have no existing published reports of SSSB to the knowledge of the authors," the researchers wrote.
66.1 percent of the reports involved male-male sexual mounting, while male-male genital touching was seen in 35.7 percent of species, and female-female sexual mounting was seen in 39.3 percent of cases.
Same-sex sexual behavior has been seen in numerous cases, ranging from bisons and dolphins to swans and penguins. SSSB appears to be more common in social species than in solitary ones, and was seen in males and females at around the same frequency.
Rhesus macaques, for example, were recently found to engage in same-sex mounting more frequently than they attempted to mount females, and one giraffe study found that up to 94 percent of all sexual mounting was between males only.
"Our survey provides preliminary evidence that SSSB occurs more frequently than what is available within the published record. While many of the experts surveyed observed SSSB in their study species, less than half of respondents recorded data on this, and a small percentage of those who recorded data have published on SSSB," the researchers wrote.
The researchers asked the responding experts why they had not recorded or published this data at the time, and discovered three general reasons: other research priorities, the behavior being too rare to be published, or it being irrelevant to their particular research topic.
"As the field of animal behaviour advances in the 21st century, methods using quantitative, statistical, and analytical approaches have been favoured over short narrative or anecdotal accounts. This could be due to an assumed lack of scientific vigor in anecdotal reporting or the worry that anecdotal reports leave room for anthropomorphism," the author wrote.
They do note, however, that over 80 percent of the respondents studied primates, which may have led to higher-than-usual reporting of same-sex sexual behavior.
"Primatologists are often interested in the study of complex social behaviours, and they may be more likely to observe, collect data on, or publish on SSSB than researchers in other fields," the researchers wrote. "Future research on this topic should aim to sample mammalian orders evenly to allow for a more comprehensive discussion of reporting trends for SSSB."
Additionally, due to the small sample size of the analysis, "the results of this survey should serve as a preliminary analysis of publication trends on SSSB," the researchers said.
However, the researchers note that this paper highlights the misconceptions surrounding the rarity of SSSB in nature, and how it may be a lot more common than the literature may make it seem.
"While SSSB was perceived to be rare in frequency by many of our respondents, it was observed by most respondents and appears to be common in many mammals. The results of this study highlight the fundamental role expert surveys play in the analysis of under-published behaviours in many subfields of behavioural ecology," they wrote.
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