Consequences of natural selection and natural reward. A Natural selection causes a change in allele frequencies, and consequently optimizes each gene to its immediate environment. B Natural reward causes a change in the total abundance of a genetic system. Here, species A does not exploit a new resource, which species B exploits. Species B expands in population and gives rise to species C, resulting in an increase in the total abundance of the genetic system ultimately shared by species B and C (blue). C Diagrams showing how species depicted in (B) track to resources. Speciation between species B and C begins with a cessation of gene flow. Species C then evolves differentially by natural selection to its new resource base.