>> As an experimental/experiential dietary researcher, I frequently have
> conversations with people who make always-unsupported claims that although
> the human is a frugivorous ape, we "adapted" to animal flesh and cooked food
> in the relatively short time that such practices have been in vogue.
How sure are we that the human is a frugiverous ape? If this statement
is not true then the rest of the discussion is not very relevant.
> Since human digestive/transport/assimilation biochemistry is a very
> complex system, I conclude it is impossible for several dozens of pathways
> to magically and simultaneously shift, or be created out of nothing, by
> stochastic mechanisms, such to be able to properly digest/assimilate animal
> flesh. In fact, humans who abandon animal products uniformly experience an
> increase in health and elimination of body/urine/fecal odors, which supports
> the conclusion that no adaptation ever took place.
I doubt that abandoning animal protein is uniformly leading to an
increase in health. Even so, the fact that meat causes changes to body
odor isn't a strong argument that humans are not adapted to eating meat.
In fact, the Inuit live on a nearly pure meat diet and their health is
poorer when they shift to a diet richer in plant components.
Also, digesting meat and vegetables are not completely different
pathways. The same proteases and lipases can hydrolyze proteins and
lipids from animal and plant tissues.
> Since the removal of genes from the gene pool can occur only by
> death-before-reproduction, and cultural diets no matter how poor do not kill
> their followers before reproductive age, there seems to be no 'selective
> mechanism' to allow such alleged 'adaptation'.
Death before reproduction, or failure to reproduce, or relatively poorer
reproduction than other individuals in the population. Poor nutrition
certainly decreases fecundity. If animal protein as part of the diet
increases fecundity you would get selection.
> Would people with scientific credibility comment on the mechanisms, or
> lack of mechanisms, necessary to 'adapt' to such non-natural dietary items?
1) I don't see that these are non-natural diets.
2) The metabolic pathways for handling the components of animal and
plant tissues are quite similar, so there is sufficient overlap that
adaptation would be a quantitative change in these proteins, not a
qualitative change leading to all new pathways.
Or at least, that's how it seems to me.