There has been much debate about whether speciation can occur without a population being physically split by some barrier. Could sufficient differences evolve among individuals within a single population to produce two species from one? This type of speciation is called sympatric speciation. Sympatric speciation has probably been responsible for producing the great diversity of cichlid fish in some African lakes. These lakes are isolated geographically from other lakes and so the diversity seen must have arisen in place from the few species that colonized the lake. The fish species are ecologically very diverse so speciation may have resulted from disruptive selection for different ecological niches.