>>> But again, and importantly, the key point here is that genetic
>>> changes in
> response to diet can be more rapid than perhaps once thought.

Some adaptations are easier than others. Going from drinking milk as a
baby to drinking it as an adult too is not such a big jump. Going from
being a small gutted omnivore eating concentrated  foods to being a
complex gutted grass eater is much greater. The argument that paleo
thinkers make is that some of the changes of the neolithic were too
great to have been completed yet. As it is we are halfway beasts. We
have started down the road, but how far any individual is on that road
is not known. If you get arthritis or diabetes in your "peak" years
from eating too much neolithic food, then you are still close to the
pre-neolithic genotype. Some people seem to have little  or no trouble
with neolithic diets. Perhaps their ancestors were under extreme
pressure that culled out the ones who didn't have the genotype that
allowed them to eat wheat and other grains.

My own ancestors, as far as anyone can know, were all northern
europeans, probably less than a few hundred years eating wheat, maybe a
thousand eating other northern grains? People from ill-fated Iraq and
the middle east may be far better adapted to neolithic foods than my
relatives.

 From a genetic aspect, shifts in gene frequencies are easy. If the gene
for something is present in the population even in very low numbers, it
can increase rapidly if conditions change to make it adaptive. A true
genetic change, a new gene mutation allowing the organism to do
something its ancestors could not do, is much much rarer and more
difficult. This second type of change is what probably has not
occurred. We are not grass eaters by nature.





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