[Lucky Dog]

Natural selection ("survival of the fittest") is one method of evolution (the change in frequency of alleles in a population). Genetic drift is another. Both genetic drift and natural selection act upon a population simultaneously. They may act upon different alleles, but there is no time when you can look at a species and say, "Now there is no natural selection, just genetic drift" or vice versa. The question is really which predominates in driving change.

Does it not seem a bit inconsistent that a theory would have multiple methods of explanation/prediction that are seemingly employed subjectively? One method is driven by “survival of the fittest” and another that is the result of “arbitrary” selection methods (dependent upon immeasurable and unpredictable issues such sexual preference), and yet another dependent upon purely random factors (such as genetic drift, etc.). When one explanation is insufficient to explain an observation, another is called upon, or if it is, likewise, insufficient, then another or, perhaps a combination. A change is subjectively judged to be the result of an arbitrary selection method or random variation if it is seemingly unimportant at the time, but, if at a later time, it seems to enhance survival, then its status is changed to critical for “survival of the fittest,” regardless of its previous status. Alternately, if a series of changes were to lead to a new species where there were no obvious “fitness” requirement criteria, then it’s back to the “genetic drift” or arbitrary selection explanation.

When you start talking about the evolution of a new phyla that's a different ball game. The genetic differences there are large enough that natural selection predominates.

Logically, why would crossing one boundary (phyla) require anything different that crossing another boundary (species)?

Your comparison to tornadoes is rather bizarre.

Quite the contrary... The appearance of a tornado can be analogous to the appearance of a new species. Without the presence of a thunderstorm (a driving requirement for “survival of the fittest”) there can be no tornado (new species). If a tornado (new species) appeared without a thunderstorm (requirement for “survival of the fittest”), then the theory is falsified.

[js1138]

Does it not seem a bit inconsistent that a theory would have multiple methods of explanation/prediction that are seemingly employed subjectively?

There is only one "explanation" for evolution: variation in the germ line plus differential reproductive success. There are many ways of dying.

[ahayes]

I'm beginning to agree with Patrick Henry.

Genetic drift is not only actively observed in populations, but through rational thought and a bit of math you can see it is predicted to occur. I'm afraid most creationists don't even know what genetic drift is, but if they do they would agree it is real.

Natural selection is also actively observed in populations and predicted to occur. Creationists likewise (sometimes only if pinned in a corner) will agree that it is real.

So what's your beef?

Logically, why would crossing one boundary (phyla) require anything different that crossing another boundary (species)?

Golly, why don't you go off for a few months and read some books?

Unless the population size is quite small genetic drift is sloooow. It dithers about here and there and takes forever to get anything done. Then when mutations occur the new alleles/genes/chromosome arrangements/etc. occur among a small number of the population. If natural selection is not present to give these novelties a boost genetic drift has the tendency to just wipe them out. In general genetic drift is the enemy of innovation.

Most major evolutionary innovations have taken place following mass extinctions. These events leave many niches wide open. Examples are the Permian-Triassic extinction, which allowed the evolution of dinosaurs; the Cretaceous-Tertiary extinction, which allowed mammals to replace the dinosaurs; and the late Devonian extinction, which was followed by the development of all modern types of plants. Some people think that the Cambrian explosion followed a Vendian-Cambrian mass extinction. The rapidity of these developments indicates natural selection was the driving force. If we waited for genetic drift to modify dinosaurs into birds we'd be waiting forever.

Remember that it is impossible to consider evolution as solely based upon natural selection or solely based upon genetic drift. Leaving out either gives a picture that is inaccurate.

And no, your thunderstorm analogy has no resemblance to reality. Mine is a much more accurate analogy.

[ahayes]

Here is an article that discusses how scientists actually determine which variations are due to genetic drift and which are due to natural selection.