Genes, development, and evolvability in primate evolution.

Development is the process whereby a fertilized cell becomes a mature individual. In metazoans, this complex process involves the differentiation of somatic cells into committed cell and tissue types; the organization and migration of cells, tissues, and anatomical structures relative to one another; and growth. Development matters to evolution in two ways. First, development carries out heritable genetic instructions contained in zygotes to produce functioning yet phenotypically varied individuals. At the population level, this variation in form and function among individuals provides the "raw material" for evolution. Second, the mechanisms of development influence the magnitude, direction, and interdependence of heritable phenotypic variation among traits. Together with phenomena such as genetic drift, organismal development determines the raw material available to selection and thus influences the rate and direction of phenotypic evolution.