Mark, it is my understanding that Sickle Cell and Thalassic Anemias are aquired, congenital, diseases that were passed on because they gave those afflicted from the disease some protection from Malaria. Sickle cell would kill you eventually, but it would allow you to live long enough to have children with the trait, while Malaria was an equal opportunity killer. For this reason they are more apt to be found in people from warm or tropical areas, like Africa, Italy and Greece, and South East Asia and the Pacific Islands.

What you might have been better off using as an example would be the distribution/frequencies of blood types, across racial lines, where I understand that there are extreme skewing of the relative distribution of various blood types from one "race" to another.

Dave