The causality of sexual orientation is probably complex and influenced by multiple factors. We advocate integrating a broader cultural perspective into evolutionary and genetic studies to explain differences in how sexual orientation is experienced, expressed and understood, both in humans and non-human animals.
The data currently available to scientists studying sexual orientation is impressive in its breadth, complexity and precision. In humans, for example, there are sequenced genomes and surveys from hundreds of thousands of individuals, as well as decades of observations from brain scans, eye-tracking, genital arousal recordings and daily digital diaries. If there were a single, simple explanation for differences in sexual orientation, it would probably have been discovered by now. The fact that this is not the case suggests the need to reassess some fundamental assumptions about the causes of variation in sexual orientation (e.g. its occurrence, function, representation, genetic basis, stability and relationship to gender).
Sexual orientation is likely to be shaped by a complex interplay of various factors. In this context, we will focus on the causes that contribute to phenotypic variation. In addition, a relatively unexplored area of research concerns the reasons and consequences of aversion to same-sex sexuality, at both individual and societal levels. Here, we discuss these historical hypotheses, the research that has overcome them, and possible directions for the future.