  We introduce and analyse an individual-based evolutionary model, in which a
population of genetically diverse organisms compete with each other for limited
resources. Through theoretical analysis and stochastic simulations, we show
that the model exhibits a pattern-forming instability which is highly amplified
by the effects of demographic noise, leading to the spontaneous formation of
genotypic clusters. This mechanism supports the thesis that stochasticity has a
central role in the formation and coherence of species.
