Depictions of Darwinian evolution (after Gould33). The classic phylogenetic tree (A) entails both adaptation (B) and elimination (C). Emphasis is commonly on the former, ontogeny, as in the display of precursors of current forms of life, with the development of modern man the paragon (D). Natural selection, however, produces many extinct species; the enormous variety and abundance of dinosaur species are underrepresented in the family tree of reptiles, and the diversity of surviving species of this class is limited (E). As Gould emphasized, our focus is on the living end product, not the lost dead ends. A physician’s parents proudly frame the baby picture with stethoscope (F), but most childhood fantasies are not fulfilled and indeed forgotten. These views of evolution apply not only to species and individual organisms but also to diverse cells and cell populations within the bone marrow.
