>But it is a rather small the place on the earth
>where our genes have formed.
>(and spread therefrom as the successfull Cro Magnon human).
>And there - in Africa - was a tropical rainforest for many millions
>of years, our anchestors were fruitarians (with little insects),
>and vegetarian nutrition *is* possible there year-round,
>as gorillas show.

I think that considering gorillas as our "ancestors" is not useful, because
they are biologically very different from humans.  In particular, their
digestive system is quite different from ours:  it has abilities to get
nutrients out of plant matter, in ways that humans can't.

A better way to look at our real ancestors would be to study the small
groups of hunter-gatherers, who still live and eat today the way they did
millions of years ago.  I believe that, among these cultures, there are
*no* vegetarians:  they all eat at least a little meat, and some live
almost entirely on animal foods.