Instability of the sexual continuum

Maynard Smith and Szathmary have posed the problem of demonstrating the conjectured instability of a continuum of sexual types with finite interbreeding. Here, I propose a model in which one can analyse exactly when and how the existence of the instability can depend on an Allee effect, and how the growth rate and typical scale of the unstable perturbations depend on the strength and range of competition, mating preference, fecundity and offspring variance due to Mendelian segregation and mutation. Instabilities of various kinds are shown to occur in the majority of parameter regimes. In short, the continuum often breaks up into incipient species.