Evolutionary Explanations for SSB

Previously, researchers have studied same-sex behavior under the pretense of Darwin’s sexual selection theory. However, the problem with this assumption and bias is that it leads scientists to believe that same-sex behavior only exists for the reproductive benefits of different-sex behavior. In other words, the purpose of same-sex behavior is to facilitate different-sex reproduction. Studying and observing organisms under this mindset will ultimately lead to bias in interpreting results. There are a few examples in which same-sex behavior has been analyzed this way, but one can see that other explanations exist by taking a closer look.
\citet{Bailey_2009} analyzed past research on the explanations of same-sex behavior and categorized them into ‘adaptive explanations’ and ‘non-adaptive explanations.’ Typical explanations of SSB argue that these behaviors are often displays of dominance (particularly in male-male interactions). The theory is that individuals display sexual behaviors to establish a hierarchy within the group. \citet{darwin1859} theory of sexual selection explained that males would compete for a female by showing aggressive behaviors and fighting. Researchers have explained male-male mounting in American Bison as a form of dominance, but male-male mounting occurs just as frequently as male-female mounting \cite{p2006}. It would be naive to think that this form of SSB solely exists as a mechanism for males to reproduce with females. An alternative explanation could be that SSB determines the herd’s social structure, which benefits the species as a whole.
Another explanation scientists have given for SSB is that males may engage in SSB to transfer their sperm indirectly to a female. In flour beetles, males were found to have engaged in SSB right before mating with females. After genetic analysis, researchers discovered that offspring carried genetics from the male that directly mated and the male that engaged in SSB with another male \cite{LEVAN_2009}. This provides an evolutionary explanation for why same-sex sexual activity may benefit a particular species, but it is uncommon.
Some animals may exhibit sexual fluidity by changing their preference for a specific sex based on the situation. For example, if individuals of one sex are entirely removed from an environment, members of the same sex might start to display SSB. In \citet{Field_2004} experiment, males kept in all-male groups for a set time engaged more frequently in SSB than did the males kept in male-female groups even after both sets of males were introduced to a male-female group. Afterward, these two groups switched - males from the all-male group were given a mixed group, and males from the mixed group were given an all-male group. The study found that after the switch, both groups of males were engaging in SSB. This example is one of many controlled experiments that sought to observe same-sex behavior in animals. However, it brings up the question - why engage in sexual activity if there are no females to reproduce with? One argument could be that these males are driven by hormones and still have the biological urge to reproduce. This would be a costly investment with no apparent benefits. Perhaps these animals are not engaging in SSB to facilitate mating with another sex but instead use it as a way to bond with other individuals and facilitate intraspecies cooperation.
These examples demonstrate that same-sex behaviors are often analyzed through the lens of Darwin’s sexual selection theory. However, this ultimately biases the interpretation of results. It is important to critically examine all viewpoints of how these behaviors may have evolved, as there may be alternative explanations.