How could a population be adapted to a situation that hadn't yet occurred?

I don't think you'll find that evidence, because the appearance of
agriculture and civilzation more or less did away with natural selection,
no?

John Pavao

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I don't think the theory implies this at all.  It does imply,
however, that when the type A mutation occurred, some 38,000
years ago, the selection pressure against it was not sufficient
to wipe it out.  That is, type As are supposedly more adapted to
an agricultural diet, but agriculture didn't arrive until 12,000
years ago, at the earliest.  So, between the appearance of type A
and the appearance of agriculture, type As were at a
disadvantage, but not a lethal disadvantage.

Now that I think of it, the theory ought to predict a greater
dispersion rate for type A blood after the appearance of
agriculture, since that would be the condition under which it
would flourish.  I wonder if the data support this...