DEVELOPMENTAL GENE-REGULATION AND THE EVOLUTION OF LARGE ANIMAL BODY PLANS

A diverse assemblage of invertebrate animals, some of which basically resemble the forms found in modern oceans, appears in the fossil recor d soon after the advent of the Cambrian period, though the first large multicellular animals clearly arose even earlier. How this occurred i s among the intellectually challenging mysteries of biology. The solut ion to this mystery is likely to emerge, in part, from an understandin g of the molecular processes by which modern animals use their genetic information to construct their body plans during embryonic developmen t, We discuss a mechanistic hypothesis that was presented earlier as a n explanation of the causal events underlying the ''Cambrian explosion ,'' and thus the divergence of large animal body plans.