Figure 1: Evolution of development of neuronal cell types.

Different events may lead to the evolution of new neuronal cell types. Duplication of a lineage doubles the amount of neurons that are generated from it; the duplicated neurons can then diversify from the ancestral ones and acquire new functions. The same is true in the case of lineage extensions, where the production of more neurons generates potential for cell speciation. Another alternative is the survival of apoptotic neurons that can then acquire distinct identities. New cell types are indicated by the horizontal stripes.