Mayr
"... It is a considerable strain on one's credulity to assume that finely balanced systems such
as certain sense organs (the eye of vertebrates, or the bird's feather) could be improved upon by random mutations."
Nilsson
"... Therefore mutations are never found in nature (e.g. not a single one of the several hundreds
of Drosophila Mutations), and therefore they are able to appear only in the favorable environment
of the experimental field or laboratory..."
Dobzhansky
"A majority of mutations, both those arising in the laboratories and those stored in natural
populations produce deteriorations of the viability, hereditary disease and monstrosities.
Such changes it would seem, can hardly serve as evolutionary building blocks."
Increased Mutation Rate
The poor Fruit Fly (Drosophila) has been radiated, heated, gassed and tortured in all imaginable
ways for nearly a hundred years - increased mutation rates of 15,000% - not a single beneficial
change observed. But thousands of bizarre changes have been created and most often the result has
been dead Fruit Flies.
(This link is really hung up on mutations)
Okay, species try to reproduce as good of copies as possible, but a lot of minor variation gets mixed in. Anytime the variation becomes extreme the creature is less likely to find a mate, and so the variations survive best when they are diffused through the population.
So when does this variation come to play, and when it is it an advantage? At various times in our planets history there have been great changes to the environment. One recently discussed at lot is the large comet that struck off the coast of Mexico 65 million years ago. This is the event that resulted in the disappearance of the dinosaurs. There have been up to a dozen of these great events, and may more of a more local nature.
When things change drasticly, when the normal food source disappears, when most of the neighbors are wiped out, when normal rules don't apply, then it is a great advantage to have variability in the genome. Those creatures which both survived the catastrophe and happened to tolerate a fair degree of variablility are presented with a new open environment. It's tough right after the problem, but then the survivers can explode upon the new landscape with little competition. Almost any can survive, even the most different of the fringe groups can find a mate and have babies. The population explodes until at some time the landscape is once again becomming crowded. Now the creatures that are a bit different can avoid the competition from their own kind but occupying niches left open by now extinct species. Those carrying the mutations that can help use otherwise unused resources will have an advantage. Those mutations will be passed on and become more prevelant. The niche users will become different from the members of their species which stayed with the old formula. This is all made possible by the easy pickings of food sources and environments left vacant by the catastrophe.
TP |
