Sickle cell trait, lactose intolerance, and alcohol sensitivity are all classic signs of selection.
Sickle cell occurs in ares where there is Malaria. People with sickle cell trait have resistance to Malaria. This is so favourable it outweighs the mortality caused when someone actually suffers from sickle cell anemia due to getting the gene from bith parents. Despite the mortaility some suffer, those with the trait are more fecund, thus the gene is common in areas with Malaria.
Dietary patterns in the West mean that anyone having lactose intolerance would fail to thrive. Those with lactose tolerance would be fecund. Thus the genes for tolerance are more common (it looks like most Westerners should call themselves lactose tolerant, as this was probably the original form, Oriental people being 'nrmal' with respect to their intolerance of lactose after weaning).
Alcohlic senstivity; same thing.
nytelecom; I know you love the little persona you wave around, but unless you improve the quality of your responses you will continue to be as intimidating as a eunuch flashing. Genetic disease and repetative strain disorders are two different things. Doh! If you're gonna be a troll, do it properly, otherwise, get with it.
People living in glass paradigms shouldn't throw stones...