Science Forums 2

[Michaelangelica]

This article has helped me understand that there is more at work than "Natural Selection". which is the point I started to make.
Darwin alone does not account for the 20C events or expansions of biological knowledge.
http://www.talkorigins.org/faqs/faq-...o-biology.html
My problem is fitting what I know into that one model
(I am still not convinced we have all the answers especially with bacteria)
But this goes some way to helping. Especially the anthropomorphizing of the word "selection"

When selection is spoken of as a force, it often seems that it is has a mind of its own; or as if it was nature personified.
This most often occurs when biologists are waxing poetic about selection. This has no place in scientific discussions of evolution.
Selection is not a guided or cognizant entity; it is simply an effect.

A related pitfall in discussing selection is anthropomorphizing on behalf of living things.
Often conscious motives are seemingly imputed to organisms, or even genes, when discussing evolution.
This happens most frequently when discussing animal behavior. Animals are often said to perform some behavior because selection will favor it.
This could more accurately worded as "animals that, due to their genetic composition, perform this behavior tend to be favored by natural selection relative to those who, due to their genetic composition, don't."
Such wording is cumbersome.
To avoid this, biologists often anthropomorphize. This is unfortunate because it often makes evolutionary arguments sound silly.
Keep in mind this is only for convenience of expression.

The phrase "survival of the fittest" is often used synonymously with natural selection. The phrase is both incomplete and misleading.
For one thing, survival is only one component of selection -- and perhaps one of the less important ones in many populations.
For example, in polygynous species, a number of males survive to reproductive age, but only a few ever mate.
Males may differ little in their ability to survive, but greatly in their ability to attract mates -- the difference in reproductive success stems mainly from the latter consideration.
Also, the word fit is often confused with physically fit.
Fitness, in an evolutionary sense, is the average reproductive output of a class of genetic variants in a gene pool. Fit does not necessarily mean biggest, fastest or strongest.

the genetics of these populations is consistant with drift models.

Thus, it is wrong to consider natural selection as the ONLY mechanism of evolution and it is also wrong to claim that natural selection is the predominant mechanism. This point is made in many genetics and evolution textbooks, for example;

"In any population, some proportion of loci are fixed at a selectively unfavorable allele because the intensity of selection is insufficient to overcome the random drift to fixation.
Very great skepticism should be maintained toward naive theories about evolution that assume that populations always or nearly always reach an optimal constitution under selection.
The existence of multiple adaptive peaks and the random fixation of less fit alleles are integral features of the evolutionary process.
Natural selection cannot be relied on to produce the best of all possible worlds." (Suzuki, D.T., Griffiths, A.J.F., Miller, J.H. and Lewontin, R.C. in An Introduction to Genetic Analysis 4th ed., W.H. Freeman, New York 1989)

And:

"One of the most important and controversial issues in population genetics is concerned with the relative importance of genetic drift and natural selection in determining evolutionary change.
The key question at stake is whether the immense genetic variety which is observable in populations of all species is inconsequential to survival and reproduction (ie. is neutral), in which case drift will be the main determinant, or whether most gene substitutions do affect fitness, in which case natural selection is the main driving force.
The arguments over this issue have been intense during the past half- century and are little nearer resolution though some would say that the drift case has become progressively stronger.
Drift by its very nature cannot be positively demonstrated. To do this it would be necessary to show that selection has definitely NOT operated, which is impossible.
Much indirect evidence has been obtained, however, which purports to favour the drift position. Firstly, and in many ways most persuasively is the molecular and biochemical evidence..." (Harrison, G.A., Tanner, J.M., Pilbeam, D.R. and Baker, P.T. in Human Biology 3rd ed. Oxford University Press 1988 pp 214-215)

The book by Harrison et al. is quite interesting because it goes on for several pages discussing the controversy.
The authors point out that it is very difficult to find clear evidence of selection in humans (the sickle cell allele is a notable exception).
In fact, it is difficult to find good evidence for selection in most organisms - most of the arguments are after the fact