Friday, December 14, 2007


Selective Facts

I've mentioned before that modern evolutionary theory, quite contrary to what propagandists like John West of the Discovery Institute would have the uninformed believe, not only was not the source of the notion of eugenics but, in fact, demonstrates that such attempts at breeding for social betterment are doomed to failure. Jim Curtsinger, a Professor in the Department of Ecology, Evolution, and Behavior at the University of Minnesota, Twin Cities, and a contributor to Minnesota Citizens for Science Education, has a nice article about West's misinformation minstrel show. At the end he gives a good explanation of why "evolutionists" don't think eugenics is part of their theory:

Enough of West's baloney – even I have limits on how much nonsense I can digest. Let's talk about real science, some very interesting stuff that is fundamental to understanding inherited human diseases. I'm speaking of the evolutionary genetic model called "mutation-selection balance", which was developed by the British evolutionary biologist, biochemist, and physiologist J.B.S. Haldane in 1927. I'll present a very simplified description here; the model is fully laid out in any standard population genetics text.

Haldane analyzed a mathematical model of an idealized population of organisms that have only one gene. Spontaneous mutations are assumed to occur in this gene at a constant, low rate. If one of the hypothetical organisms happens to inherit two copies of the mutated gene, it has an inherited disease and does not survive to reproduce.

From the point of view of the gene pool, two processes are going on simultaneously in Haldane's model: spontaneous mutation is dumping "bad" alleles into the gene pool every generation, and selection is cleaning them up at a certain rate through the deaths of carriers. What is not obvious but was shown mathematically by Haldane is that the gene pool gradually evolves to a state where the rate of input of deleterious mutations is precisely balanced by the rate at which they are removed by natural selection (hence the name of the model). An equilibrium frequency of deleterious mutations is reached.

Haldane's insight has important implications for understanding inherited human diseases. There are thousands of different diseases, but fortunately for us, each is rare. This occurs because with realistic mutation rates the equilibrium level of deleterious alleles attained in the mutation-selection balance model is always low, significantly less than one percent. Though rare, the deleterious recessive mutations are always there, a permanent fixture of the gene pool. This helps explain the bad effects of inbreeding, since close relatives have increased chances of carrying the same mutations. This result also says that negative eugenics can never clean up the gene pool completely. In particular, even if a society were to screen everyone every generation and prohibit any carriers of deleterious mutations from reproducing, that would still never completely eliminate the mutation - it would only reduce the frequency somewhat, at unthinkable social cost. Negative eugenics can't purify the human gene pool.
Not that the Discovery Institute or its band of blatherers are interested in anything as inconvenient as the truth.

Via Pharyngula.

Comments: Post a Comment

<< Home

This page is powered by Blogger. Isn't yours?

. . . . .


How to Support Science Education