Gradualism in Evolution (was Categories ...) (Agnosticism)

by David Turell , Saturday, July 31, 2010, 14:25 @ George Jelliss

dhw: "Either innovations work or they don’t, and if they do, they are already complex, even if they survive and later become even more complex. It therefore seems to me that evolution doesn’t depend on gradualism at all. Perhaps someone can enlighten me."

There is a section in Ernst Mayr's "What Evolution Is" that deals with this subject, though as I've said before I'm not a biologist and I find the language difficult to follow. He points out that: "individuals in a single population may differ by visibly different characters" (he cites eye colour and number of molars). He continues: "A successful mutation with a large phenotypic effect can be gradually incorporated into a population as long as it is able to pass through a period of polymorphism in which it coexists with the previous phenotype, until it has completely displaced the original gene." He ends with "it must be remembered that there is a considerable range in the size of the mutations that lead to evolutionary change". Later on he says: "Darwinian gradualism is due to the gradual restructuring of populations."

The rediscovery of Tadpole shrimp in Scotland, a 200 million year-old species, unchanged for all that time is an example of what? How does an organism decide it is perfect for its environmnt and make no changes for 200 million years? Saying 'stasis' identifies the issue or does it? Punctuated equilibrium doesn't help either. This is not gradualism. Nothing before and nothing after. Mutation just disappears in this animal, or no mutation achieved a necessary change. This is really what the fossil record is like. Trilobites with their double eye lenses for 250 million years, appear and then disappear. Nothing in this view suggests gradualism.

http://www.guardian.co.uk/environment/2010/jul/29/rare-tadpole-shrimps-found-scotland