Same-sex sexual behaviour is often described as an ‘evolutionary paradox’, a ‘mystery’, a ‘conundrum’ … but is it, really? The Bailey lab investigates evolutionary causes and consequences of same-sex sexual behaviour and has examined its plasticity and genetics in fruit flies, the role of sex discrimination in crickets and termites, and more recently the natural and life history correlates of its expression using comparative approaches. It is so taxonomically widespread, it’s more of a mystery when we don’t see it. Our research group are finding that when you look, you find. Lab members have recently observed same-sex sexual behaviours that are completely undescribed, including in different-sex sexual contexts. How do we classify these behaviours? A major direction of future research is examining plasticity of same-sex sexual behaviour from an evolutionary perspective. As with most complex behavioural traits, heritability is low to moderate, meaning the overwhelming majority of variance in its expression is explained by the environment, not genetics.