Re: Genetic Evolution (was: HGHG)
Lane Singer (lsd@ix.netcom.com)
30 Jan 1995 07:58:36 GMT
In <tlathropD36L2I.3sA@netcom.com> tlathrop@netcom.com (Tom Lathrop) writes:
[continued from previous post]
>But Lane ignores something else just as important, which is that the
>map of human relatedness that Cavalli-Sforza *does* come up with, after
>all his careful statistical analysis, looks a great deal like the
>racial classifications physical anthropologists came up with years
>ago!
Yes, because as I illustrated in a previous post, when confronted with
genetic data on almost 2,000 populations, he began pooling them on
a geographical basis. And, he used the names to identify them that
were present in the sources for much of the genetic data upon which
"The History and Geography of Human Genes" was based. By the
way, he ended up with 42 populations. Are you defining them as
42 different races?
Also, I should like to remind you that he comes up with numerous
maps.
> His strongest conclusion is that the deepest genetic division in
>the human race lies between Africans and non-Africans. His genetic
>trees typically divide first into African and non-African branches, and
>then the non-African branch divides into a South-Asian/Australian
>branch and a North-Asian/European branch. "Europeans" or "Caucasoids"
>generally have a branch of their own, and the main area of confusion
>seems to be Asia, with the relationship between north and south Asia
>unclear.
I know this African/non-African split is of some significance to you,
however to Cavalli-Sforza et al its only import is that it "suggests that
the split between Africans and non-Africans was the earliest in human
evolutionary history."
>These genetic trees and graphs, and the relationships they represent,
>form one of the major conclusions of the book. Lane has simply blown
>them off, because they are not what he wants to see.
I have blown nothing off. I would like to focus on the issue of the
Europeans, for just a moment. Cavalli-Sforza et al state in numerous
passages that the arm leading to the Europeans is quite short, genetically:
"There are three possible explanations for this phenomenon: a smaller
evolutionary rate in the European branch, a bias resulting from the
selection of all markers among European samples, or admixture
between two populations of the tree leading to the formation of
Europeans.
"In the last 5000-6000 years, Europe was densely inhabited, and
the resulting decreased drift may have lessended the evolutionary
rate."
The book contains a very clear discussion on the effects of population
density on the rate of evolution by random genetic drift.
They go on to state, however, that even if drift were completely frozen
it wouldn't explain all of the shortness of the link, meaning the closeness
of Europeans to Africans.
In pursuing the possibility of admixture, another study is cited that
turned up evidence of an Asian-African source for Europeans,
with 65% Asian and 35% (subSaharan) African.
So Europeans are genetically similar in many was to both Asians
and Africans, only slightly less evolution has taken place as a result
of the effects of population density on random genetic drift.
>But how is it
>possible, if surface features are indeed "superficial", that physical
>anthropologists who had little else to work with should have arrived at
>conclusions so close to those Cavalli-Sforza arrived at by analyzing
>genes?
Because climate is a factor in any specific geography. The early
attempts to define race were based entirely on skin, hair, bones &c,
all surface traits that respond to climate. When Cavalli-Sforza
created 42 populations to study, he did it by taking 2000 populations
and pooling them on a geographic basis. There's very little more to it
than that, however much you seem to want to read a great deal into
it.
By the way, exactly which racial definition are you referring to?
The early anthropologists had many. If you're going to keep citing
one, perhaps you should include it, along with its source.
>I think it is because they never relied on just *one* trait, but tried
>to look at as many as possible. If you group by just dark skin alone,
>your results are unreasonable. If you group by dark skin, tightly
>curled hair, a broad nose and thick lips, then you come up with
>Africans and some of the people of Oceania.
In other words, what do they look like and where do they live. That
should cover it. BTW, aren't you "obsessing over physical traits?"
> Make an educated guess
>that these groups are too far apart to be related (which turns out to
>be correct), and you've replicated one of Cavalli-Sforza's groupings
>(although not his conclusion that Africans form one of the two main
>branches of humanity).
Oh no, they wouldn't have imagined Africans to form the basis of
all humanity. That would have required that they drop all manner
of racist notions, so they could start carfully examining the fossil
evidence in Africa, something that =was= within their capability,
even if genetics wasn't.
>Note BTW that it isn't necessarily true that *all* racial features
>respond quickly to climate. Skin color and body build certainly do,
>but what about hair form, or the epicanthic eye fold and characteristic
>facial bone structure of Asians?
Have you read any of the followups to your "Those Eyes" thread?
I haven't seen you respond to many. The general consensus is
that eye folds are to be found in many populations outside of Asia,
including Africa and Europe. Facial bone structure is responsive
to climate, by the way. (More "obsessing", Tom?)
> At least some racial features
>probably did arise after the races separated, and *do* trace separate
>lineages.
What are you attempting to convey here?
>Anyway, I've spent more time on this quote than I intended to, and I
>want to remind Lane that I had *two* main points in my post that I
>wanted him to respond to. He took a weak stab at one elsewhere (my
>query as to how long *he* thought it would take for a 15 point IQ
>difference to arise between two separated populations),
You haven't responded to my post on that. I believe I did have some
questions in there for you.
> but he has
>entirely ignored the other, which is that while genetic variation
>between races may account for only 6 percent of total human genetic
>variation, this number is highly dependent on how much variation
>existed in the ancestral human population prior to racial
>diversification, and tells us little about how important the
>differences between different racial groups might be.
This seems like a good topic for another post.
> He also has yet
>to explain Cavalli-Sforza's use of the word "hierarchy" to describe how
>his "population clusters" are structured, and what this does to the
>argument that the notion of race must be meaningless because the number
>of racial groups you can come up with is arbitrary.
I think I have discussed Cavilli-Sforza's view of this. Do you have
something to add?
>In fact, it seems
>that *most* of the points I made in my post have gone unanswered.
>Maybe I should just repost it. >:->
Singer
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