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.