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Seems we pretty much agree on the basic facts as to what this 'mutation' does. What we disagree on is (1) whether it is beneficial and (2) whether it verifies the theory of evolution. As to (1) losing a 1/4 of the children does not seem very beneficial to me. In addition it must be remembered that people without this 'protective' mutation nevertheless survive in malaria infested regions. So this is not necessary for survival.

Yes, we do agree on the function of this mutation. Thank you.

However, as we are discussing "survival of the fittest", I think sickle-cell anemia falls well within this criteria. Natural selection does not always result in a decrease in genetic variation. If this were so, then balanced polymorphism would not be seen in populations such as the Black-Bellied Seedcrackers of Cameroon, West Africa.

In the case of sickle-cell anemia, heterozygotes have the distinct advantage, with up to 35% of the population in a region where malaria is evident displaying heterozygote resistance, with only about 4% of the population being homozygous and therefore afflicted with the disease. Indeed, other individuals without the Hb-S allele do survive, but I'm sure you would agree that living organisms have a variety of survival mechanisms available to them. Humans do not overcome the flu, for instance, solely because of antibodies...fever, nutritional status, age, etc. all contribute to the survival of the individual.

As to (2) it cannot be said to verify evolution because it destroys normal operation of the organism. It does not create anything new. Evolution needs lots of new stuff to be true, not the destruction of stuff.

Hmmm...I'm not sure I follow you on this point. "Normal" operation of an organism is survival, and the heterozygous resistance to malaria conferred by the Hb-S allele clearly facilitates survival in these individuals.

Natural selection does not always result in a decrease in genetic variation. If this were so, then balanced polymorphism would not be seen in populations such as the Black-Bellied Seedcrackers of Cameroon, West Africa.

I must strongly disagree with your statement about natural selection, the dead do not reproduce so their genetic information is lost - and not just the trait that brought destruction, but other traits that might have been beneficial. Further, since even the traits that caused destruction might have been useful if circumstances had been different (and circumstances always change) this is also a loss to the species.

Yes, that is pretty much what it means. However, let's consider this - is malarial infection prevalent everywhere on earth? Clearly not. So outside of malarial areas, this mutation is bad since it may result in death to progeny if two people carrying it have children. We see that problem now with blacks in the US where it is of no benefit at all. So if this trait were spread throughout the whole human species, it would be seriously detrimental to humanity. That's what I meant.