On the role of ecology in mating systems: freeing the study of sexual behaviour from bias

The world is full of sexual diversity. Attempting to understand the extraordinary multiplicity of sexual behaviours and morphologies we see in the natural world can be overwhelming. The scientific community clearly needs generalized conceptual frameworks to help categorize patterns and explain this diversity. However, patterns can sometimes be overgeneralized, oversimplified or overinterpreted. Here we consider the tension between the simplifying principles used by evolutionary biologists and the exuberant diversity of sexual behaviours we see in nature. We scrutinize how anisogamy and the Darwin–Bateman paradigm have shaped our thinking, resulting in the theory of ‘the sexual cascade’. While they have informed our understanding of sexual competition, the emergence and conflicts of the sexes and the resulting diversity of traits shaped by sexual selection, these frameworks do a rather limited job of predicting specific sexual and other reproductive behaviours. Instead, they can reinforce biases about how we expect female and male animals to behave. For instance, competitive or choosy sexual behaviours map rather poorly to one sex or the other across a broad range of species, as evidenced by our growing awareness of male mate choice and female–female competition for gametes. We argue that the ecological context of a species remains central to linking life-history investment, from the gamete onwards, to mating behaviour and the processes of sexual selection. As researchers and educators, we need to remember that apparently broad patterns across taxa may have limited utility as specific predictors of the diverse sexual behaviours that amaze and beguile us, and that useful theoretical abstractions do not replace a full understanding of sexual behaviour.