Developmental gene regulation and the evolution of large animal body plans

SYNOPSIS. A diverse assemblage of invertebrate animals, some of which basically resemble the forms found in modern oceans, appears in the fossil record soon after the advent of the Cambrian period, though the first large multicellular animals clearly arose even earlier. How this occurred is among the intellectually challenging mysteries of biology. The solution to this mystery is likely to emerge, in part, from an understanding of the molecular processes by which modern animals use their genetic information to construct their body plans during embryonic development. We discuss a mechanistic hypothesis that was presented earlier as an explanation of the causal events underlying the "Cambrian explosion, " and thus the divergence of large animal body plans