Introduction

Darwin’s theory of evolution explains that natural selection favors organisms with a high probability of survival and the ability to pass genes down to their offspring through reproduction \cite{darwin1998}. This theory is widely accepted and has become a core part of any course about evolution. \citet{darwin1859} theory of evolution suggests that individuals of high ‘fitness’ will pass their genetics to offspring by mating with individuals with gametes compatible for fertilization (e.g., egg and sperm). Same-sex behavior (SSB) often does not lead to reproduction, yet it has been documented in over 1500 species of animals \cite{Monk_2019}.

Scientists have long searched for a genetic explanation for same-sex behavior in humans, aiming to find a gene or genetic trait that can be inherited and passed down to offspring. Most of these studies have come up short, with little to no evidence of a “gay gene” \cite{harris2019}. This further confuses scientists that seek to understand how same-sex behavior evolved without any apparent “benefits.” We must also consider that different-sex behavior (DSB) is not always initiated for reproduction purposes. However, this costly sexual activity is prevalent among most organisms. Why do we differentiate between same-sex and different-sex behavior if neither leads to reproduction?

\citet{Monk_2019} offer an alternative perspective of the origins of same-sex behavior from being a ‘Darwinian paradox.’ Under Darwin’s theory, the biological costs of same-sex behavior would have eradicated it over time because of a lack of reproductive benefits. \citet{Monk_2019} explain how same-sex behavior and different-sex behavior evolved together instead of SSB evolving from DSB. When male-female, monogamous relationships are used as the baseline for animal mating behavior, same-sex behaviors are seen as abnormal or unusual. The understanding that male-female relationships are the norm and default is known as heteronormativity. This can harm the research of these animals and any queer person that adopts this mentality. If we shift our perspective to view same-sex behaviors as normal, we can reconceptualize biological sex and sexual activity in animals and prevent bias in research.