On Sat, 3 May 2003 23:59:41 +0000 (UTC), nonlinear5{at}yahoo.com (Eugene
Kononov) wrote:

>Hey guys,
>
>I don't know much about genetics, so I am turning to you to help me
>with this problem.
>
>[moderator's 'ello: Watch it, right? - JAH]
>
>Suppose you want to verify a biological/philosophical theory that the
>humans are imperfect because they still have a recessive gene that
>comes from incest between some close relatives of Adam and Eve. Assume
>also that it happened about 6,000 years ago. If you need an estimate
>of the number of generations in 6,000 years, take 250. According to
>the laws of genetic evolution (if there are any), what are the chances
>that this recessive gene is still in the current generation of people?
>
>I'll do the math myself, I just want to know some probabilistic
>formula/rule that a particular gene mutates (completely, partially?).
>
>Thanks,
>Eugene.

First of all, you must understand that, under the breeding plan
described, incest is inevitable.  Who did Adam and Eve's children mate
with?  What about the grandchildren?  With such a tiny population, all
offspring of one original pair, there is no alternative.  After a few
generations, cousin-cousin matings of different degrees of inbreeding
become possible.

Second, you have another problem in the genetics.  If the gene in
question is what makes us imperfect (or sinners) and if it is truly
recessive, then the heterozygote (with only one copy of that allele)
would actually be perfect.  So if all humans are imperfect (sinners?)
and the gene is recessive, then all humans are homozygotes.  That
means, there is no alternative allele -- both Adam and Eve were
imperfect, possessing two copies of the 'imperfect' allele so all
their offspring would be.  The allele will never be eliminated.  Any
other interpretation of the genetics (whether the gene is dominant or
recessive or shows some intermediate inheritance, whether it is sex
linked or autosomal, whether it shows epistasis or some other strange
genetic characteristic) if there is more than one allele, then
necessarily some humans would be perfect and some imperfect. And,
according to some ways of thinking, that is false.  So there are no
alternative alleles.

Third, you must understand that, according to the Hardy-Weinberg
equilibrium, if the recessive gene is neutral in fitness (neither
advantageous nor disadvantageous) then it should remain in constant
frequency in the population.  Of course, that assumes a large
population so in the early generations you have to calculate the
probability that genetic drift will eliminate the recessive allele.
But let's just look at the present day with a large population.  Then
a neutral allele will remain in the gene pool at a constant frequency.
Obviously, having the "imperfect" allele does not reduce ones
fertility and therefore it is not deleterious.  It may even lead to
lust, and therefore be advantageous. In any case, unless there were
selection against the trait, it would not be eliminated.

Fourth, even with selection against this allele, in large populations
natural selection actually works quite slowly.  Hardly anything
happens in just a few hundred generations unless the fitness
differences are quite unusually large.  Ordinarily it takes thousands
of generations to produce even small genetic (evolutionary) change.
That is, in the history of human civilization (only a few thousand
years) there really hasn't been any significant evolution.  Over
hundreds of thousands of years (10,000 generations or more), then you
can accumulate some real changes and over millions of generations
evolution can do quite a lot.
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