02.28.06
Body Plans
Why has there has been so little change in major body plans since the Early Cambrian, while great changes have subsequently occurred within phyla and classes? Two US biologists observe, “Classic evolutionary theory, based on selection of small incremental changes, has sought explanations by extrapolation from observed patterns of adaptation. Macroevolutionary theories have largely invoked multi-level selection, among species and among clades. But neither class of explanation provides an explanation of evolution in terms of mechanistic changes in the genetic regulatory program for development of the body plan, where it must lie.” They believe that handfuls of genes they call the “kernels” of gene regulatory networks “must have been assembled during the initial diversification of the Bilateria …but …they would have become refractory to subsequent change.” All of this is unsurprising for strong panspermia.