phyletic evolution[fī′led·ik ‚ev·ə′lü·shən]
a type of evolution characterized by the gradual change, without divergence, of an entire group of organisms. The term “phyletic evolution” was proposed by the American paleontologist G. Simpson, who distinguished it from speciation, the divergent development of two or more daughter species from a single parent species. However, it is now recognized that speciation occurs even with phyletic evolution, but the new species are formed successively, over a significant period of time. Phyletic evolution is usually characterized by moderate or low evolution rates and is detected when one studies the evolution of supraspeciestaxons.