Hi Gary, and all,
You may well be correct about several types of selection pressure. But I'm
going to disagree with the position you take on dietary adaptation
generating only weak pressure. I have an 1889 report on celiac disease,  by
Dr. R. A. Gibbons, in which   he states:
"Prognosis- Unfortunately this is usually grave, and the majority of
children suffering from this disease die." (page 328)


Gibbons R, "The Coeliac Affection in Children" _Edinburgh Medical Journal_
vol. XXXV; no IV:321-330: 1889

Since celiac disease is a function of dietary adaptation, it is one trait
relating to dietary adaptation which would be expected to exert some very
strong selective pressure. And what about infant milk allergy? Prior to
this century, that would be likely to exert some fairly strong selective
pressure.
Best Wishes,
Ron Hoggan


> Many traits relating to dietary adaptation would be
>expected to generate only weak selective pressure since they primarily
>affect us after our reproductive years. Given the chance, genetic drift
>could act as an "accelerator" on the evolution of such traits.