On Fri, 18 Jul 1997, Toby Martin wrote:

> Todd Moody wrote:
> > Again, the fact of neoteny may not be the whole story.  The
> > explosion of agriculture has subjected most of the human race to
> > intense selection pressures.
>
> I don't understand why this would be the case. Can you explain?

I can try.

As Ray Audette and Troy Gilchrist point out very well, the
agricultural revolution was a very phenomenon in its effects on
humankind.  On the positive side, it made possible and necessary
many of the things that we now recognize as basic ingredients of
civilization: literacy, surplus and leisure, extensive division
of labor, etc.  These things may not be entirely positive, but
I'm not going to argue that point.  Agriculture makes possible an
entirely different way of life, which has benefits and costs.
Among the costs are the health consequences of the altered diet.

To the extent that some genetic strains of humans are better
adapted to the new diet, they would have a selective advantage.
Not only would they be less sick than others, but they would tend
to live longer.  Long-lived people provide much that is of value
to their kin, and thus to their gene pool.  There *is* selection
pressure in favor of longevity beyond prime childbearing age.

Those families that held up better under the strain of the
agricultural diet would tend to grow and prosper; those families
made sicker by the agricultural diet would tend to dwindle.  This
differential success is selection pressure.  In a world in which
infant and childhood mortality rates are high, the family that
has healthy grandparents and even great grandparents to help with
the child rearing and other tasks has a distinct advantage over
the family in which the adults succumb at a young age to
diet-related disorders, hence the intensity of the selction
pressure.

Of course, selection pressure doesn't *create* adaptation; it
only favors it.  For adaptation to happen there must be the right
sorts of variations, occurring with sufficient frequency.  The
sort of dietary adaptations that we are discussing would come
under the heading of microevolution, and this is precisely the
domain in which saltational models of evolution work best.  I
therefore think it is not out of the question that some strains
of human beings have evolved away from being adapted to the
paleolithic diet.

The blood type theory comes to mind here, but I have no idea
whether there is any merit to the idea that blood types are
markers of dietary adaptation.

Todd Moody
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