On 7/8/97 Dean Esmay wrote:

>...Evolution DOES occur, and if the
>selective pressure is HIGH (let's say a very extreme dietary change that
>kills people quick who don't adapt), you can see changes in a fairly short
>period of time.

I was told recently that evolution (change in genetic makeup) can occur by
at least 4 other mechanisms besides selective pressure. I don't remember
all of them, but one that is thought to be particularly relevant to human
evolution is something called "genetic drift". This is a sort of random
sampling situation, where the normal distribution of genes in a population
is biased by passing through a numbers bottleneck - in the case of humans,
usually either a significant die-off or migration of a sub-group. (For
example, if I have 10 balls, 5 red and 5 blue, and I discard 6 of them, the
remaining 4 will not necessarily have the original 50:50 distribution of
red and blue.)

Such a process allows for the appearance and distribution of genotypes that
seem unreasonable given normal selection. Basically, you don't have to have
high selection pressure for a gene to evolve, particularly within a
population subgroup. Many traits relating to dietary adaptation would be
expected to generate only weak selective pressure since they primarily
affect us after our reproductive years. Given the chance, genetic drift
could act as an "accelerator" on the evolution of such traits.

Gary