Animal genitalia are highly variable, even among closely related taxonomic groups.

Much of this variation is thought to be attributable to sexual selection, either because genitalia function to help sperm compete for fertilisations, or because they are subject to evolutionary sexual arms races (sexual conflict).

We use a range of methods, including behaviour, comparative approaches, quantitative genetics and experimental evolution to reveal patterns of selection on animal genitalia and the selective processes that underlie their rapid and divergent evolution.

We study genital evolution in a range of model systems, including livebearing fishes, house mice, insects and millipedes. Our behavioural studies have revealed how intricate structures associated with male and female genital traits are associated with patterns of mate choice, mating success and paternity, thus supporting the view that sexual selection is likely to be a potent evolutionary force shaping selection on animal genitalia.

Our ongoing quantitative genetic studies increasingly reveal high levels of genetic variation underlying the expression of male and female genital morphologies in insects and livebearing fishes, thus confirming the evolutionary potential of these traits.

Studies of experimental evolution, particularly in insects and house mice, have revealed strong evidence for rapid evolutionary responses to sexual selection. Meanwhile, our work on internally fertilising fishes (guppies) suggests that sexual conflict may generate an evolutionary arms race between male and female genital morphologies.

Our studies of millipede genitalia are showing how divergence in genital morphology among populations can lead to reproductive isolation, and ultimately speciation.