(urth) Mystery of Ascia

[Lee Berman]

Gerry we are a bit closer to understanding on these issues. I misunderstood what you were
getting at with "natural country type". I thought you meant there could be no prevalent 
variation of a gene in a certain region. Now I understand you are arguing that there is more
than one possible adaptation that can help a population to live in a given environment. And
of course that is true. Large body size, Hunter's response, brown adipose tissue, epicanthic
folds, large nose, light skin; all these have been argued as cold weather adaptations in humans
and a given population in a cold environment can have any of them (though I don't know of any
which have all of them in high frequency).
 
A couple misundertandings on your part: 
 
> Genes are copied faithfully person to person. Mutations are almost always harmful
 
>Not true.  Here, for example, is Wikipedia on the subject of alleles:"It is now appreciated that most 
>or all gene loci are highly polymorphic, with multiple alleles, whose frequencies vary from population 
>to population, and that a great deal of genetic variation is hidden in the form of alleles 
>that do not produce obvious phenotypic differences.">
 
First it should be understood that "allele" is not a synonym for "gene". An allele is defined as a gene
variant. Second it should be understood that "phenotype" refers to the outward expression of a gene.
 
So, Wikipedia is saying that there can be a lot of gene variation where the difference doesn't DO 
anything. This relates to the idea of "junk DNA". If a gene is not expressed, it it not subject to
natural selection. It can just sit there and be copied or mutated from generation to generation and it 
doesn't matter.
 
With certain traits which don't have a selection pressure on them, like eye color or blood type, there
are various alleles like blue/brown or A-B-O. But for stuff that matters, like the code for insulin or
the code for having 5 fingers alternate alleles (diabetes and 6 fingers) are selected against and are
rare.
 
But this is not what we are talking about. We are talking about high frequency genes which have obvious 
phenotypic effects and which are subject to selection and, as a result, show regional variation in 
frequency like skin color (btw, there is probably no adaptive advantage to blue eyes and blonde hair;
they are just accidental by-products of the gene for low melanin production in the dermis). There is no
"African" melanin or "Swedish" melanin" or "Turkish" melanin or whatever. It is the same pigment in all
humans (and many other animals as well). There is no irreversible variant of melanin that will make one
population of humans forever different than others.
 
Anyway, those are just side issues. The main issue you are not getting is that there can be no inherent 
"irreversibility" of gene frequency within a species. By definition it is not possible because 
the potential for admixture exists. With admixture and selection, any particular gene in a regional
population of a species can go from 0% to 100% and back to 0% as long as the gene exists somewhere
on earth for that species.
 
You can't argue that artificially isolating a group of Swedes and a group of Africans in a cage for
infinity years constitutes an example of Dollo's Law of irreversibility. It makes no sense. A scientific 
law must describe what happens in nature. It must have an element of predictability. For your experiment 
to create irreversibility your caged individuals must become different species. So different that there is 
never a possibility of interbreeding. This has already been discussed and it must be understood or there is
no point in discussion.
 
I get the impression you were hoping Dollo's Law might make it impossible for lighter skinned people to
ever look like their African ancestors even if global warming turns the whole planet into a tropical
rain forest or something like that. It just isn't the case. As long as we remain one, potentially 
interbreeding species, it is possible for the whole of humanity to end up falling anywhere in the range of 
the spectrum of variability. We could all become light skinned, all dark skinned, all curly haired, all 
straight haired, all blue eyed, all brown eyed, etc.
 
I think Chances are highest that our diverse genome will maintain a diverse outer appearance but there is 
no way to know what the future selection pressure will be. No way to know which genes will get turned on
which will get turned off nor in what frequency. But as long as we remain one species there is no
irreversibility.