(urth) Mystery of Ascia

[Gerry Quinn]

From: "Lee Berman" <severiansola at hotmail.com>
> Gerry Quinn wrote:

>>(1) 50000 years or 2000 generations is in fact a quite substantial time
>>in human evolutionary history, and it is rather obvious that significant
>>genetic changes have taken place in human populations over such 
>>timescales.
>
> The sort of evolutionary change from which Dollo's Law was formulated 
> takes 10's
> of millions of years. Humans and chimpanzees share 98% of the same genetic 
> code.
> This amount of change is currently estimated to have taken around 18 
> million years.

Dollo's Law was formulated before the days of molecular genetics, but it is 
easily generalised.  Essentially it is a statement about the irreversibility 
of evolution, and its truth or otherwise can be observed on any scale on 
which one cares to look, including evolutionatu changes taking place over 
quite short timescales.  The key issue is irreversibility.

Your 98% figure is essentially meaningless.  From human to chimpanzee is a 
considerable difference, at least according to criteria which would be 
considered important by humans and chimpanzees.  If by some definition, the 
genetic difference is only 2%, all it proves is that 2% is a huge 
difference, and much smaller differences would be important.

What matters is not the numeric value, as measured by whatever criterion, 
but the net effect on phenotype.


> The huge amount of genetic difference many people assume exist among 
> modern
> Homo sapiens sapiens is largely an illusion perpetrated by dietary and 
> other
> environmental differences, clothing and hair style differences, and a 
> xenophobic
> bias which pushes us to exaggerate visual differences, probably an ancient
> tribal recognition trait.

Certainly some people ezaggerate the difference between races (or whatever 
other paradigm they use to describe genetic differences among populations). 
On the other hand, it is equally true that many people - including not a few 
scientists -  falsely minimise these differences, presumably taking the view 
that interracial harmony is more important than scientific truth.  It's by 
no means obvious that their lies (or at least statements carefully designed 
to mislead) do indeed lead to interracial harmony, though.


> Swedes and Africans were not genetically separated for 50,000 and thus are 
> even
> closer than the 99.998% similarity that time frame suggests. Walking seems 
> like
> slow transportation but given thousands of years it works quite well to 
> provide a
> genetic continuity across our entire species. And anywhere you can walk or 
> boat,
> you can walk or boat back.

In the first place, your figure of "99.998% similarity" is both wrong and 
irrelevant.

In the second place, you seem to be setting a lot of store by the fact that 
geographiically separated populations may not be completely separated. 
Absence of complete separation does not in any way preclude genetic drift 
between populations  The most obvious counterexamples are 'ring species':

>From Wikipedia:
In biology, a ring species is a connected series of neighboring populations, 
each of which can interbreed with closely sited related populations, but for 
which there exist at least two "end" populations in the series, which are 
too distantly related to interbreed, though there is a potential gene flow 
between each "linked" species. Such 
non-breeding-though-genetically-connected "end" populations may co-exist in 
the same region thus closing a "ring".

Ring species clearly give the lie to your notion that the possibility of 
occasional interbreeding eliminates the possibility of significant genetic 
drift.

Another thing giving the lie to it was mentioned already - the existence of 
human populations with considerably different phenotypes side by side - e.g. 
Pygmies and larger peoples.


> As a thought experiment, let's pretend an experimenter grabbed a random 
> sample of
> 1000 babies from the different races and sub-races around the globe that 
> people (though
> not scientists) say they recognize. All those babies are raised in an 
> isolated commune
> with the same diet, sunlight exposure, clothing, hairstyle etc. As adults, 
> this commune
> would not have recognizable "races". It would demonstrate a single species 
> with slight
> gradations of diversity, which is what the world population of humanity 
> is, from a
> genetic perspective. It is only when you focus exclusively on extremes and 
> ignore
> gradations and environmental and cultural differences that genetic "races" 
> can be
> "clearly" identified.

Are you seriously proposing that the genetic heritage of these children 
would somehow disappear?  Adopted children of different racial origin from 
their parents are commonly reared in their parents community.  They don't 
develop all the phenotypical features of their adoptive parents!


>>In fact, even if we ignore genetic drift within Homo Sapiens lineages,
>>current thinking is that 1-4% of the genetic heritage of European and 
>>Asian
>>populations come from outcrossing with the subspecies Homo 
>>Neanderthalensis.
>
> There has been much debate in the past 50 years but the current majority 
> opinion is that
> Homo neanderthalensis (proper nomenclature= genus capitalized, species 
> lower-case)
> was, as that name implies, a different species than Homo sapiens sapiens. 
> Meaning
> there was no interbreeding. Neanderthals originated in Africa then spread 
> out as far
> as Europe. Later, Homo sapiens evolved in Africa and spread out even 
> further.

The new research was in the news lately.  Here's a link to a news report:
   http://news.bbc.co.uk/2/hi/science/nature/8660940.stm
Of course it might be proven incorrect, but what it says is exactly what I 
stated.


> It is just hypothesis. There is no way to know, without experimentation, 
> whether Homo sapiens
> and neanderthals 1. could not produce offspring (like humans and chimps)* 
> or 2. could only
> produce sterile mules (like horses and donkeys) or 3. actually could 
> interbreed with viable
> offspring.
>
> It doesn't matter. If "neanderthal genes" are present in the Homo sapiens 
> gene pool they
> have been spread across our species, not concentrated in Europe or 
> something like that.

The research indicates where they have spread, and where they have not. 
Specifically, they found the Neanderthal genes in French, Chinese and Papuan 
populations, and not in San or Yoruba populations from sub-Saharan Africa.


> The occasional (might be 1 in 10 million) dark baby born to light parents 
> in Sweden or pale
> baby born to dark parents in Africa and the even rarer occasion of a baby 
> born with a tail
> demonstrates that the genetic potential of our ancestors remains in our 
> genome, waiting to
> be turned on, whether by accident, or perhaps someday, by necessity.

Yes, but the genes of a dark-skinned baby from Swedish stock, while they 
will probably lead to the expression of melanin of some kind, will probably 
be differnt in some ways to the genes currently expressed by the various 
dark-skinned races.  They are likely to lead to the production of different 
kinds of melanin in differnt proportions. Like I said, a tribe of Swedes 
that moved to Africa would eventually grow dark skinned, but they would look 
different from nearby tribes.  There is no 'natural country type'. 
Irreversibility of evolution (the generalised principle of Dollo's Law) says 
so.

- Gerry Quinn