Craig Smith wrote:
>
> Keith wrote:
>
> >So, he says, we don't know fro
> >m evolution whether serious obesity is
> >incurable.  No one - as far as we know - was ever born seriously obese, he
> >adds; they get this way.  Modern society makes it easy for the obese and
> >other people who could not survive in the Pleistocene to reproduce and it
> >may be that this expansion in human reproductive choices will lead to a
> >genetically [rather than environmentally] inherited obesity.


I recall an experiment done with sparrows in captivity. They
were allowed to reproduce freely, with plenty of food and no
predators. Within just a few generations the size of the
sparrows had changed greatly, in both directions. Some were
far larger, and some far smaller than wild sparrows. The
selection forces normally kept them within a very narrow
range, but the genetic diversity was there to allow very
different sparrows to appear under new conditions. When
these sparrows were exposed to wild conditions, the extremes
died off and the normal sized ones again predominated.

I am probably an example the other way from overweight, I
was always underweight, didn't even make the minimum on the
charts for my height/weight ratio as a kid, as I recall. For
a Sudanese I might have been average, but for a Northern
European I am very lean. In paleolithic times I probably
would have been too skinny to stay warm. But then again, I
would have been eating very different foods then, so maybe
not...

We still face considerable selection pressure, but not on
body size so much. Currently we face considerably more
selection pressure from disease than paleo people ever did.
Paleo people dodged rhinos; we drive cars. Much the same
reflexes involved, and similar rates of death I suppose. Our
social pressure is very great too, many people in modern
times never marry, or put  it off so long that they never
have kids. This will have an evolutionary effect if it
continues several generations.