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For parents who each carry the sickle cell trait, the chance that their child will also have the trait -- and be immune to malaria -- is 50 percent. There is a 25 percent chance that the child will have neither sickle cell anemia nor the trait which enables immunity to malaria. Finally, the chances that their child will have two copies of the gene, and therefore sickle cell anemia, is also 25 percent. This situation is a stark example of genetic compromise, or an evolutionary "trade-off."

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. 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.

whether it is beneficial...whether it verifies the theory of evolution...

All I'm saying is that sickle-cell is an example of mutation and natural selection at work. If it weren't beneficial in the Darwinian sense, it wouldn't occur in 40% of some populations. Do you have another explanation to account for the fact it is found in a fairly large percentage of people in malaria country, but in a very small (zero, really) percentage outside it?

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.

No-one said, and I explicitly denied, that hemoglobin-S is the *only* protection against malaria.

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.