Richard Archer wrote:

>Imagine a population of 100,000 in which a mutation occurs.
>Assume the mutation has a 50% chance of being passed on to offspring.
>Also assume the mutation gives the bearer a 2% advantage over a non-bearer.
>This advantage could be a greater fertility rate, a resistance to a
disease,
>a greater ability to raise young etc.
>
>That mutation will have 'infected' 10% of the population after 471
generations.
>Would this be where middle-eastern humans are now - 10% grain tolerant?

Please correct me if I am wrong, as your two hour crash course in genetics
is more than I can boast (since college), but I think you have the whole
idea of advantageous mutations and subsequent reproductive gene transmission
upside down.  You propose hypothetically that 10,000 years ago, all middle
easterners  (100%) experienced a mutation that resulted in a slight
advantage that has a 50% chance of being passed on to offspring.  From that
point, you seem to infer, prevalence of this mutated gene would dwindle to a
current 10%.

As I see it, the way it actually works is totally different.  First of all,
mutations don't happen all at once to a whole population.  The mutogens
encountered in the environment from individual to individual are varied, and
even in the case of group exposure there still exists the element of
individual variability in the immune system's ability to repair and maintain
DNA.  Thus, any given population has a certain degree of random genetic
variation at any given time.

Upon exposure to selective pressure in the form of an environmental change
like high grain consumtion, a fraction of a given population, perhaps a very
small one, may be lucky enough to exist on that portion of the random
genetic variation curve that contains a mutated gene that allows the them to
fare slightly (or otherwise)better in the face of the environmental change.
Over time, this lucky fraction of the population has slightly better luck at
reproduction and thus grows in number.  Those who are among the unlucky
experience slightly dwindling numbers until eventually the mutation prevails
and the population as a whole has adapted.  You have to remember that, even
given only a 50% transmission to offspring rate, a suficiently advantageous
mutation prospers from less direct mechanisms.  For example, the fittest
individuals (those with the mutation) are more likely to mate with others
who are most fit, and advantaged couples are likely to have more offspring
than normal couples.  This is oversimplified, but I think that you can get
the general idea.

B. Lischer