Explaining variation in Darwinian evolution

American Scientist Online interviews Marc W. Kirschner and John C. Gerhart, authors of The Plausibility of Life: Resolving Darwin’s Dilemma.

Can you describe the new theory [of “facilitated variation”] briefly?

Our theory addresses the most mysterious part of Darwin’s theory of evolution, namely “variation.” As you may recall, he postulated that small differences of form and function inexorably arise among individuals in any group of animals. One individual, bearing its variation, may be more fit than others of the group to survive and reproduce in the environment at hand. In time, its descendants out-reproduce the others and come to replace them.

About half a century ago, we learned that heritable variation does not occur without mutation. Any place in the genome can suffer mutation, which is a change of the local DNA sequence. It appears to strike at random, and rarely. Our theory of “facilitated variation” is meant to explain how rare and random mutation can lead to exquisite changes of form and function.

We give center place to the fundamental processes by which animals develop from the egg to the adult and by which they function as adults. These are the “conserved core processes.” They make and operate the animal, and surprisingly they are pretty much the same whether we scrutinize a jellyfish or a human. There are a few hundred kinds of processes, each involving tens of active components. Each component is encoded by a gene of the animal’s genome, thus using up the majority of the 20,000 genes possessed by complex animals such as frogs, mice and humans.