This chapter begins by considering the Maynard Smith model. Much of this work concentrated on the genetic mechanisms for assortative mating and reproductive isolation, based on the assumption that the underlying niche ecology would generate disruptive selection. However, understanding the conditions under which disruptive selection arises in the first place is equally important, and indeed necessary for assessing whether diversification is a general outcome in the Maynard Smith model. The chapter then shows that disruptive selection and polymorphism are scenarios that occur generically, that is, for a wide range of parameters, in a classical and widely used speciation model. It also provides an introduction to some of the basic concepts of adaptive dynamics theory.
