The official blog of University of Missouri Skeptics, Atheists, Secular Humanists, & Agnostics
The first chapter of WDGW lays out the structure of the so-called ‘modern synthesis,’ which construes natural selection as a two part, single dimensional process: First, genetic mutations arise randomly; second, external environmental factors ‘select’ phenotypes. The authors bring evidence from genetics to bear on this model. They argue that the internal elements of the process are hardly random, and that much of the evolutionary process rides on non-random internal constraints at the genetic level.
Much of the support for their claims comes in the form of quotes from contemporary geneticists, to the effect that much of the ‘filtering’ occurs internally, rather than externally through the organism’s environment. They likewise criticize the idea that variations in one trait are independent from heritable variations in other traits, arguing instead that the packaging of traits within the chromosome is messily interconnected (this is my poor attempt at a summary).
The authors spend much time discussing evolutionary development, or evo-devo. I found some of this discussion fascinating, particularly regarding the idea that entire life cycles are the the objects of evolutionary forces, not merely the adult forms. Rather than the organism’s adult form being the primary phenotype that undergoes selective pressures, evo-devo regards each developmental step as part of the filtering process, from the fertilized egg to the adult.
Much of the material in chapter one is technical, and I found it rather difficult to follow. I’ve re-read it several times, but I still do not grasp all of the arguments.
Chapter two zooms out, so to speak, from gene complexes to entire genomes and more complex systems. The authors continue to emphasize the role internal constraints play in the evolutionary process. They point to the robustness of ‘master genes’ and gene networks, which offer alternative explanations for evolutionary change. Rather than the random phenotype generation plus external filter model, they push a model of shifting internal networks and structures not easily influenced by the environment to any great degree. They take the primary targets of their criticism to be gradualism and adaptationism, of which I know Dawkins and Dennett are champions. I’ll say more about chapters two and three in the next post.