On Sat, 5 Sep 1998, T. Martin wrote:

> Ok, got it. What threw me off in your original phrasing was that
> "pressure to adapt to local conditions is extreme" in an isolated
> breeding population. The way I see it, the pressure comes from the
> environment, and is therefore extreme in both isolated and non-
> isolated populations: a large portion of each new generation does
> not survive to reproduce.

Yes, that's right.  I think I just didn't express the point very
well.  The fact that a large portion of each new generation does
not survive to reproduce can quickly wipe out an I-pop.

> In the I pop, on the underhand, pressure is strong only at first.
> If the pop survives, later generations will be adapted to the
> environment (which no longer seems harsh). Genetic change is rapid
> at first, and slows down as equilibrium is reached.
>
> Does this sound right?

Exactly.  That was the main point.  In an I-pop under harsh
conditions there is a forced choice between *rapid* adaptation
and extinction.

I should also add that the assertion I made about isolation
preventing genetic drift was exactly wrong.  Isolation *favors*
genetic drift, but genetic drift wasn't the idea that I was
trying to get at.  Rather, it was the idea that in a small and
isolated breeding population, the gene pool is necesarily smaller
and doesn't get enrichment from other populations.  This stacks
the deck against adaptation at first, but if adaptation
nevertheless occurs it also keeps it local.

In the context of diet and nutrition, we have to think about this
in terms of the magnitude of changes necessary for adaptation.
Consider a diet of all or mostly meat versus a diet that makes
extensive use of plant foods.  Both diets are "paleo" but they
make different demands on the body.  Most obviously, the all-meat
diet is ketogenic and thus requires the body to function well in
ketosis.  Adaptation to such a diet would involve *optimizing*
for ketosis.  What would that mean?  It would mean shifting the
balance of enzymes in the direction of readiness to deal with
large amounts of protein and fat.  It would also mean an
adaptation for more efficient gluconeogenesis to provide the
glucose that is absolutely needed.  It would mean adaptation in
the direction of maximum retention of those vitamins and minerals
that would be in short supply on an all-meat diet.

Now consider a population that consumes even a modest amount of
vegetation, i.e., more than about 50g of carbs per day.  These
people will almost never be in ketosis, except when they are
going hungry.

If you think about just these two populations, one living in
almost constant ketosis and the other almost never in ketosis, it
wouldn't be exactly unexpected to find divergent adaptation,
since their bodies are being required to function well in quite
different states.  A similar point might be made about diets very
low in fiber versus diets very high in fiber, I think.  Why would
we expect an Australian aborigine, whose traditional diet is low
in meat but high in fibrous vegetation to do well on the Inuit
diet?  Personally, I *wouldn't* expect it.  Why do the aborigines
and Inuit suffer from even higher rates of diabetes and other
diseases than the rest of us, when exposed to civilized diets?
Why aren't their disease rates the same as ours?  The obvious
answer is that they are even less adapted to civilized diet than
we are.  Why should we assume that they are well adapted to each
other's diet?

Moral of the story:  Paleolithic nutrition comprises a spectrum
of possibilities.  There is no good reason to suppose that any
diet on that spectrum will match the nutritional needs of every
person.  The trick is to find the one that does.  It is made
trickier by the fact that the foods available to us are often
rather different from the ones that we are best adapted to.

But it makes life interesting.

Todd Moody
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