On Fri, 24 Apr 1998, Aaron D. Wieland wrote:

> I
> suspect that resistance to disease may be the main selective pressure
> affecting blood type distribution.

This is the received view, I think.

> Since certain illnesses would have been
> most common in agricultural societies, this may have resulted in a spurious
> correlation between blood type and metabolic type.

I don't think I follow you here.  Could you explain your idea a
bit more?

> I'm another Type A who fared very poorly on a "Type A" vegetarian diet, so I
> share the skepticism of others on this list.  As Todd suggested, the blood
> type diet confounds two issues: (1) sensitivity to particular foods, and (2)
> metabolic needs.

And I'm sure you have noted that it's difficult or impossible to
find any pattern to the lectin sensitivities, from an
evolutionary standpoint.  Bananas are okay for Os but not As.
Strawberries are okay for As but not Os.  I have to wonder if,
from purely a lectin standpoint, there has ever been a population
of humans that avoided all or even most of their "bad" lectins.
It seems doubtful.  Presumably, type O hunter-gatherers ate
blackberries when they could get them, and ate strawberries when
they could get them, and cauliflower and coconuts and many of the
other things on the type O "avoid" list.  This suggests that the
lectins, in themselves, were not creating much selection
pressure.

On the other hand, the lectins appear to behave exactly as
Neanderthin's "foreign proteins" are supposed to behave.  So much
so that I am inclined to think that the foreign protein and
lectin theories stand or fall together.

Neanderthin is also a mixed bag, of course.  Although obesity is
claimed to be an autoimmune disease, it seems that avoidance of
foreign proteins is not sufficient to cure it.  For that, lowcarb
dietary principles must be followed, even though they have
nothing specifically to do with autoimmunity or, for that matter,
paleolithic eating.  We know that not all hunter-gatherer diets
are lowcarb.

But I digress...

> Blood type may in fact be correlated with metabolic needs,
> but there are many exceptions.  From an evolutionary perspective, it makes
> little sense that within a population, in which everyone ate the same foods
> for thousands of years, there would be sub-groups with completely different
> dietary needs; hunting tofu was not an option for the Blackfoot.

That's a good point, and well worth thinking about.  It may be
that the key thing is to *vary* the lectins by varying the plant
foods as much as possible and not allowing any one set of lectins
to be continuously pushing the same immunological buttons.

Todd Moody
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