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Author Topic:   Human Races
NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 121 of 274 (69581)
11-27-2003 9:41 AM
Reply to: Message 119 by Peter
11-27-2003 3:34 AM


I'm not talking about 3-4 major divisions. I find that too
broad ...
And isn't that where this whole thing started?
If there is a new definition of the races of humans perhaps you could supply it? At least clearly enough so that we can tell how many there are.

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 Message 119 by Peter, posted 11-27-2003 3:34 AM Peter has seen this message but not replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 122 of 274 (69594)
11-27-2003 10:59 AM
Reply to: Message 120 by Mammuthus
11-27-2003 8:42 AM


I'm sure Ned won't mind
I felt that the part that spoke about why the within/between
comparison isn't relevant was stated better than I had.
Maybe I was wrong.
Consensus is hardly a validation of anything -- a couple
hundred years ago the concensus was that the earth was flat.
You've mentioned 'clearly divergent' a few times -- I asked how
different populations needed to be for this, but I think
you missed it in the rush to respond to the rest of the
posts.
The differences which we see as 'race' in terms of racial
description are localised geographically wrt origin of the
lineages (biological).
Biological lineages can be traced genetically (e.g. the Viking
study that found a correlation with the known interaction
with the Danes and the boundaries of the Dane-Law).
The differences are related to locally adaptive traits, and are
heritable.
If you look at non-coding sequences (which the within/between
paper cited earlier in the thread did) you are not looking
at the areas responsible for the 'racial' differentiation.
If you accept out-of-africa then you must accept divergence
of the human populations, else the differentiation that is visibly
present (and heritable) couldn't exist.
That divergence does correlate with the racial distinctions
commonly made -- including those with only 3 categories (is that
a particulalry US thing in the UK we now use a 16 + 1
categorisation for such things.)
That there is more variatey amongst Africans than between
Africans and Eurpoeans (say) is not evidence of a lack of
race, but evidence of a lack of refinement.

This message is a reply to:
 Message 120 by Mammuthus, posted 11-27-2003 8:42 AM Mammuthus has not replied

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sfs
Member (Idle past 2533 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 123 of 274 (69654)
11-27-2003 11:49 PM
Reply to: Message 119 by Peter
11-27-2003 3:34 AM


quote:
The following nicely sums up my objection to the rejection of
human races as a biological concept as argued in this thread.
I will admit though (to save time) that this paper agrees that
the link between cultural concepts of race and a meaningful
biological one is likely not there.
Since that's precisely what you're arguing, the paper would appear to undercut your position.
quote:
I tend to disagree with that aspect of the paper, simply because
the commonly held view of what makes races of humanity different
focusses on 'adaptive' differences.
Really? I'm not aware of any good evidence that any of the commonly used differences, apart from skin color, is the result of adaptation.
I have a couple of problems with your use of this paper. First, recall that your claim was that there is a genetic basis to what we call race. These authors disagree, unless you mean something very peculiar by "we". They explicitly state that human races, in the meaning given to the term by human geneticists, in the meaning given by anthropologists, and in the popular meaning, are not real biological entities. Instead, they argue that human populations do qualify under quite a different definition of race, one that makes it equivalent to "ecotype". (Why they think it's important to make such a seemingly pointless argument I haven't got a clue.)
The second problem is related to the first. The definition of race that you would like to defend is based on clusters of traits, while the authors again explicitly state that different traits do not naturally form the same group. A phylogenetically based race will tend to share a suite of traits, while a race that is characterized only by a common selective environment will not, since different selective pressures vary differently with geography.
In their words, "And of course, as has already been noted, insofar as folk races are supposed to pick out populations that systematically differ from each other over a wide range of genetic and phenotypic measures, biology provides no support for the existence of such populations (and indeed, provides evidence that no such populations exist)." And, "Of course, this implies that insofar as we focus on an ecotype conception of race, there will not necessarily be a unique 'race' to which any given member of a population belongs. Any given individual may in fact belong to a number of different ecotypic races, and/or be a member of one (or more) intermediate population(s) within a (series of) clinal distribution(s)."

This message is a reply to:
 Message 119 by Peter, posted 11-27-2003 3:34 AM Peter has replied

Replies to this message:
 Message 125 by Peter, posted 11-28-2003 4:10 AM sfs has replied

  
sfs
Member (Idle past 2533 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 124 of 274 (69655)
11-27-2003 11:57 PM
Reply to: Message 122 by Peter
11-27-2003 10:59 AM


quote:
Consensus is hardly a validation of anything -- a couple
hundred years ago the concensus was that the earth was flat.
There's been a consensus in the West, at least, that the Earth is spherical for over two thousand years.
quote:
Biological lineages can be traced genetically (e.g. the Viking
study that found a correlation with the known interaction
with the Danes and the boundaries of the Dane-Law).
The differences are related to locally adaptive traits, and are
heritable.
Differences between Scandanavians and Anglo-Saxons are related to locally adaptive traits? Like what? The differences that were used to distinguish Scandanavian genetic contributions were not functional one. You've confused definitions of race again: the distinction between Scandanavians and Anglo-Saxons is a phylogenetic one, while the definition of race you've just been supporting is an adaptive one. You just used two different definitions in two sentences.

This message is a reply to:
 Message 122 by Peter, posted 11-27-2003 10:59 AM Peter has seen this message but not replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 125 of 274 (69674)
11-28-2003 4:10 AM
Reply to: Message 123 by sfs
11-27-2003 11:49 PM


quote:
Since that's precisely what you're arguing, the paper would appear to undercut your position.
...the reason is not linked to greater difference within and
between populations though.
quote:
Really? I'm not aware of any good evidence that any of the commonly used differences, apart from skin color, is the result of adaptation.
So distinctive differences in physiology, bone stucture, muscle
attachment, etc. are just random coincidence and not the
result of some past selective pressure?
quote:
A phylogenetically based race will tend to share a suite of traits, while a race that is characterized only by a common selective environment will not, since different selective pressures vary differently with geography.
So a population that has been subject to the same selective
pressures will NOT share a set of traits?
And two different populations living in environments with
different selective pressures won't diverge (even remotely ...
perhaps I can call it nano-evolution )?
If there was concensus in the west for a spherical earth for
two thousand years, how is that people thought Columbus was
going to fall off the egde if he went too far?
Sure, the Greeks and other ancient races knew, but in Europe
as recently as, what, three - four hundred years ago, the majority
opinion was Earth was flat.
Consensus isn't enough. It can be shaped by political factors
and fear of reprisal.
I'll restate my position (hopefully with any contradictions
removed, and consider this my thinking even if my meadering
thought processes have obfuscated my thinking in previous posts).
1) Cultural racial membership is defined by the members of a
perceived race (not by outsiders). The UK government is using
a 'self-declaration' race categorisation, and the US hospital
services have performed studies that show, by-and-large, that
self-determined racial categorisation matches standard
admission rankings.
2) Cultural racial associations are linked to the history
of the cultural race.
3) Cultural races originate in localised geographic regions. Each
geographic region will present somewhat different survival
challenges.
4) Extant phenotypic traits that interact with the environment will,
over time, be shaped by the environment. These traits are, by
definition, heritable.
5) If there is a noticeable difference in the pehnotypic traits
of one group compared to another, then this must be identifiable
in the coding segments of the genome.
We, as humans, are observably different.
Those differences are heritable.
Those differences are what cultural racial concepts refer to.

This message is a reply to:
 Message 123 by sfs, posted 11-27-2003 11:49 PM sfs has replied

Replies to this message:
 Message 127 by sfs, posted 11-29-2003 3:42 PM Peter has replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 126 of 274 (69677)
11-28-2003 4:22 AM


And what about ....
Nature - Not Found
"They discovered that the most recent common ancestor of everyone in the sample group lived in Africa 171,500 50,000 years ago. They also found a significant branch in the tree that separates most Africans from non-Africans. This genetic divide probably represents an exodus of people from Africa that took place 52,000 27,500 years ago."

  
sfs
Member (Idle past 2533 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 127 of 274 (69893)
11-29-2003 3:42 PM
Reply to: Message 125 by Peter
11-28-2003 4:10 AM


quote:
So distinctive differences in physiology, bone stucture, muscle
attachment, etc. are just random coincidence and not the
result of some past selective pressure?
Quite possibly. Also quite possibly not. Determining whether any particular trait in real-life populations is the result of selection or not is actually quite difficult, except in the most extreme cases. Most human traits are in the "we don't know" category. Even the evidence for selection for skin color is a little tenuous.
quote:
So a population that has been subject to the same selective
pressures will NOT share a set of traits?
A single population subject to the same set of selective pressures will probably share a set of traits. But different selective pressures are unlikely to have exactly the same geographical distribution, which is why the paper you quoted from talks about membership in multiple, overlapping races. Some environmental factors change over very short distances, while others remain similar over thousands of miles.
quote:
If there was concensus in the west for a spherical earth for
two thousand years, how is that people thought Columbus was
going to fall off the egde if he went too far?
They didn't. The whole flat-earth thing was a product of tendentious (and crappy) nineteenth century antireligious efforts at history. The reason people thought Columbus would fail was that he was using the wrong value for the diameter of the Earth. (The more commonly accepted value was around 25,000 miles, and was quite accurate; he was using a much smaller estimate (18,000 miles? I forget). Both estimates were made by the ancient Greeks.) There's no evidence that anybody in Europe three or four hundred years ago thought that the Earth was flat. Uneducated peasants might have thought so (they might still think so in some places, for all I know), but nobody bothered to record what peasants thought. The educated knew better. (You probably mean more than than three or four hundred years, by the way -- the first circumnavigation of the globe was completed well over 400 years ago.)
I'll deal with your substantive comments latter. Right now my kids are harassing me to read to them.

This message is a reply to:
 Message 125 by Peter, posted 11-28-2003 4:10 AM Peter has replied

Replies to this message:
 Message 128 by Peter, posted 12-02-2003 6:09 AM sfs has replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 128 of 274 (70527)
12-02-2003 6:09 AM
Reply to: Message 127 by sfs
11-29-2003 3:42 PM


quote:
Quite possibly. Also quite possibly not
So your rejection of the traits being adaptive is as incorrect
as my suggestion that they are.
Can we positively identify ANy traits as adaptive except by
a significant amount of hypothesising?
quote:
A single population subject to the same set of selective pressures will probably share a set of traits. But different selective pressures are unlikely to have exactly the same geographical distribution, which is why the paper you quoted from talks about membership in multiple, overlapping races. Some environmental factors change over very short distances, while others remain similar over thousands of miles.
And in regard to a biological basis for race, this is more pro
than contra.
If geographic separation subjects different groups to different
sets fo selective pressures, then the populations that are
affected by those pressures will share trait sets that populations
elsewhere do not have.
quote:
They didn't.
Fair enough ... doesn't detract from concensus being a poor
metric for a theory.
How about a geocentric solar system then ... or bleeding being
a beneficial therapy ... or ...

This message is a reply to:
 Message 127 by sfs, posted 11-29-2003 3:42 PM sfs has replied

Replies to this message:
 Message 129 by sfs, posted 12-02-2003 4:05 PM Peter has replied

  
sfs
Member (Idle past 2533 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 129 of 274 (70615)
12-02-2003 4:05 PM
Reply to: Message 128 by Peter
12-02-2003 6:09 AM


quote:
So your rejection of the traits being adaptive is as incorrect
as my suggestion that they are.
Had I stated such a rejection, it would have been incorrect. I didn't, so your comment does not apply. I just reject labeling traits as adaptive until we have evidence that they are.
quote:
Can we positively identify ANy traits as adaptive except by
a significant amount of hypothesising?
We can make a good case, but only when there's enough genetic evidence. E.g. "Detecting recent positive selection in the human genome from haplotype structure." (Sabeti et al., Nature. 2002 Oct 24;419(6909):832-7.) Without doing the work, however, it's just a bunch of guesses.
quote:
If geographic separation subjects different groups to different
sets fo selective pressures, then the populations that are
affected by those pressures will share trait sets that populations
elsewhere do not have.
Could you be more specific? Identify some groups that are the sort that you think could be considered races, and identify their distinctive environmental conditions. That would give me a much clearer idea of what you mean.
quote:
doesn't detract from concensus being a poor
metric for a theory.
Sure. It's the evidence that counts, not the consensus.

This message is a reply to:
 Message 128 by Peter, posted 12-02-2003 6:09 AM Peter has replied

Replies to this message:
 Message 130 by Peter, posted 12-03-2003 4:15 AM sfs has replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 130 of 274 (70709)
12-03-2003 4:15 AM
Reply to: Message 129 by sfs
12-02-2003 4:05 PM


quote:
Really? I'm not aware of any good evidence that any of the commonly used differences, apart from skin color, is the result of adaptation.
Had I stated such a rejection...
Sorry, mis-interpreted the above as you saying that they
weren't rather than we don't have evidence that they are.
quote:
We can make a good case, but only when there's enough genetic evidence
Darwin didn't have the luxury of genetic evidence, and yet he could
still infer adaptive traits from observation of traits wrt
environment ... isn't that sufficient? If a trait provides a benefit
of some kind in the environment where it is the norm?
Isn't the emergence of differentiation between two populations
of the same species in different locations required by evolutionary
theory ... and it's absence an undermining of such?
quote:
Could you be more specific? ...
Inuit :- live in harsh, cold environment with limited vegitation.
Kalahari Bushmen :- live in harsh, desert environment some game, some
fruit/nuts/edible roots.
Celts :- Originated in cold, wet hilly location unsuitable for much
agriculture.
The locations on earth are many and varied, and the peoples who
come from different locations are observably different, but
consistent within group.
quote:
It's the evidence that counts, not the consensus
That's all I was saying. Consensus was raised as though that
made it true ... I am unconvinced by the suggested evidence.

This message is a reply to:
 Message 129 by sfs, posted 12-02-2003 4:05 PM sfs has replied

Replies to this message:
 Message 131 by Mammuthus, posted 12-04-2003 4:33 AM Peter has replied
 Message 133 by sfs, posted 12-04-2003 1:48 PM Peter has replied

  
Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 131 of 274 (70931)
12-04-2003 4:33 AM
Reply to: Message 130 by Peter
12-03-2003 4:15 AM


quote:
Darwin didn't have the luxury of genetic evidence, and yet he could
still infer adaptive traits from observation of traits wrt
environment ... isn't that sufficient? If a trait provides a benefit
of some kind in the environment where it is the norm?
Isn't the emergence of differentiation between two populations
of the same species in different locations required by evolutionary
theory ... and it's absence an undermining of such?
Darwin's inferences on adaptive traits were mere speculation. As sfa pointed out, it is extremely difficult to identify adaptive traits. Merely saying some trait must be the cause of reproductive success is not sufficient since multiple traits vary simultaneously and figuring out which one or ones are adaptive is not trivial for example,
: J Exp Biol. 2001 Sep;204(Pt 18):3151-60. Related Articles, Links
Genetic approaches to understanding human adaptation to altitude in the Andes.
Rupert JL, Hochachka PW.
Department of Pathology and Laboratory Medicine, The University of British Columbia, Vancouver, Canada V6T 2B5. rupert@zoology.ubc.ca
Despite the initial discomfort often experienced by visitors to high altitude, humans have occupied the Andean altiplano for more than 10000 years, and millions of people, indigenous and otherwise, currently live on these plains, high in the mountains of South America, at altitudes exceeding 3000 m. While, to some extent, acclimatization can accommodate the one-third decrease in oxygen availability, having been born and raised at altitude appears to confer a substantial advantage in high-altitude performance compared with having been born and raised at sea level. A number of characteristics have been postulated to contribute to a high-altitude Andean phenotype; however, the relative contributions of developmental adaptation (within the individual) and genetic adaptation (within the population of which the individual is part) to the acquisition of this phenotype have yet to be resolved. A complex trait is influenced by multiple genetic and environmental factors and, in humans, it is inherently very difficult to determine what proportion of the trait is dictated by an individual's genetic heritage and what proportion develops in response to the environment in which the person is born and raised. Looking for changes in putative adaptations in vertically migrant populations, determining the heritability of putative adaptive traits and genetic association analyses have all been used to evaluate the relative contributions of nurture and nature to the Andean phenotype. As the evidence for a genetic contribution to high-altitude adaptation in humans has been the subject of several recent reviews, this article instead focuses on the methodology that has been employed to isolate the effects of 'nature' from those of 'nurture' on the acquisition of the high-altitude phenotype in Andean natives (Quechua and Aymara). The principles and assumptions underlying the various approaches, as well as some of the inherent strengths and weaknesses of each, are briefly discussed.
quote:
The locations on earth are many and varied, and the peoples who
come from different locations are observably different, but
consistent within group.
Consistent within group??? You are kidding right?
J Clin Endocrinol Metab. 2001 Jun;86(6):2747-51. Related Articles, Links
Common genomic variation in LMNA modulates indexes of obesity in Inuit.
Hegele RA, Huff MW, Young TK.
John P. Robarts Research Institute, London, Ontario, Canada N6A 5K8. robert.hegele@rri.on.ca
We discovered that rare mutations in LMNA, which encodes lamins A and C, underlie autosomal dominant Dunnigan-type familial partial lipodystrophy. Because familial partial lipodystrophy is an extreme example of genetically disturbed adipocyte differentiation, it is possible that common variation in LMNA is associated with obesity-related phenotypes. We subsequently discovered a common single nucleotide polymorphism (SNP) in LMNA, namely 1908C/T, which was associated with obesity-related traits in Canadian Oji-Cree. We now report association of this LMNA SNP with anthropometric indexes in 186 nondiabetic Canadian Inuit. We found that physical indexes of obesity, such as body mass index, waist circumference, waist to hip circumference ratio, subscapular skinfold thickness, and subscapular to triceps skinfold thickness ratio were each significantly higher among Inuit subjects with the LMNA 1908T allele than in subjects with the 1908C/1908C genotype. For each significantly associated obesity-related trait, the LMNA 1908C/T SNP genotype accounted for between approximately 10--100% of the attributable variation. The results indicate that common genetic variation in LMNA is an important determinant of obesity-related quantitative traits.
Glad all those Inuit are genetically identical....especially those inconsistent ones in the population.

This message is a reply to:
 Message 130 by Peter, posted 12-03-2003 4:15 AM Peter has replied

Replies to this message:
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Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 132 of 274 (70943)
12-04-2003 7:43 AM
Reply to: Message 131 by Mammuthus
12-04-2003 4:33 AM


'Genetic approaches to understanding human adaptation to altitude in the Andes.'
Talks about the difficulty of determining whether or not
a trait is developmental or 'built-in'.
Is that the same as inferring whether a trait is adaptive or
not, if one already knows that the trait is genetically
linked (based of heritability, for example)?
If a heritable trait confers an advantage, and only occurs
in individuals who trace their family origins back to
the same location is that insufficient evidence of an adaptive
trait?
Off topic maybe?
quote:
"We discovered that rare mutations in LMNA.."
Who said anything about genetically identicle ... since when did
consistent mean the same?
The paper you cited is talking about 'rare mutations'. One would
hardly classify a drosophila with stunted wings as anyhing
but a mutant drosophila, why change the 'rules' for humans?
If you have a whole bunch of red-eyed ones and a whole bunch
of white-eyed ones of the same species they are referred to as
strains (aren't they) ... why change the 'rules' for people?

This message is a reply to:
 Message 131 by Mammuthus, posted 12-04-2003 4:33 AM Mammuthus has not replied

  
sfs
Member (Idle past 2533 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 133 of 274 (71004)
12-04-2003 1:48 PM
Reply to: Message 130 by Peter
12-03-2003 4:15 AM


Re: Engineering special: take whatever it has at that point.
quote:
Darwin didn't have the luxury of genetic evidence, and yet he could
still infer adaptive traits from observation of traits wrt
environment ... isn't that sufficient? If a trait provides a benefit
of some kind in the environment where it is the norm?
Just showing that there's a benefit is not usually enough -- and showing that a trait is beneficial is pretty difficult in itself in humans. There are cases where the circumstantial evidence is good enough that it's pretty persuasive; the persistence of lactose tolerance in populations that have historically practiced dairy-farming is a good example. I can't think of any that are markers for racial groups, however.
quote:
Isn't the emergence of differentiation between two populations
of the same species in different locations required by evolutionary
theory ... and it's absence an undermining of such?
That depends on how recently the populations have separated and how much gene flow there is between them.
quote:
Inuit :- live in harsh, cold environment with limited vegitation.
An environment they share with a number of other ethnic groups. Are they all one race, or are they many races? I would say that the Inuit are a group that has shared a similar enough environment and has been isolated enough that they might have distinctive adaptive allele. Then again, they might not -- they might share adaptive alleles with other arctic groups, for example. Is there any evidence that they do have distinctive, adaptive alleles?
quote:
Kalahari Bushmen :- live in harsh, desert environment some game, some
fruit/nuts/edible roots.
This is a better example of more typical human populations. "Bushmen" is not a category that they would use to self-identify -- it's a grouping invented by European colonists. They're confined to the Kalahari primarily because they've been pushed there by recent pressure, so it's not at all clear that there's any reason they would have unique adaptations for desert life. San-speaking groups originally inhabited all of southern Africa. They admixed heavily with agriculturalists arriving from farther north; some groups retained San languages, others northern languages, but all were genetically mixed.
quote:
Celts :- Originated in cold, wet hilly location unsuitable for much agriculture.
Really bad example. Many or most self-identified Celts today have little or no genetic inheritance from the original Celts. I'm not sure where you mean by the cold, wet hilly location they originated -- do you mean southern Germany? Or the Asian steppes, where they may have come from earlier? To the extent that they are a genetically identifiable population, they don't seem to have stuck around anywhere for very long, so it makes no sense to talk about unique environmental pressures for them.

This message is a reply to:
 Message 130 by Peter, posted 12-03-2003 4:15 AM Peter has replied

Replies to this message:
 Message 134 by Rei, posted 12-04-2003 1:59 PM sfs has replied
 Message 137 by Peter, posted 12-05-2003 3:13 AM sfs has replied

  
Rei
Member (Idle past 7013 days)
Posts: 1546
From: Iowa City, IA
Joined: 09-03-2003


Message 134 of 274 (71005)
12-04-2003 1:59 PM
Reply to: Message 133 by sfs
12-04-2003 1:48 PM


Re: Engineering special: take whatever it has at that point.
quote:
There are cases where the circumstantial evidence is good enough that it's pretty persuasive; the persistence of lactose tolerance in populations that have historically practiced dairy-farming is a good example. I can't think of any that are markers for racial groups, however.
Let's just ignore disease adaptations (like sickle cell) for now; probably the most frequently used racial identifier - skin color - does have regional dependence. Skin color is based on a balance between two issues: genetic damage from UV light (having extra melanin absorbs the light, and reduces the risk of damage), and vitamin-D synthesis (which melanin inhibits). In regions with more annual light intensity, darker skin is adapted for; in regions with less annual light intensity, lighter skin is.
I agree, though, that there is no distinct point where one can make a fair delimitation; it's a gradient of allele frequency, which varies depending on which gene you're talking about.
------------------
"Illuminant light,
illuminate me."

This message is a reply to:
 Message 133 by sfs, posted 12-04-2003 1:48 PM sfs has replied

Replies to this message:
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sfs
Member (Idle past 2533 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 135 of 274 (71089)
12-04-2003 11:06 PM
Reply to: Message 134 by Rei
12-04-2003 1:59 PM


quote:
Let's just ignore disease adaptations (like sickle cell) for now; probably the most frequently used racial identifier - skin color - does have regional dependence. Skin color is based on a balance between two issues: genetic damage from UV light (having extra melanin absorbs the light, and reduces the risk of damage), and vitamin-D synthesis (which melanin inhibits). In regions with more annual light intensity, darker skin is adapted for; in regions with less annual light intensity, lighter skin is.
Sorry, I wasn't clear -- I'd already agreed several posts back that skin color is probably adaptive (dark color quite likely, light color less so -- it's possible it just represents a relaxed constraint, not positive selection). It's not at all clear to me that it does represent a racial marker, in the sense that he's using "race" here, or at least that it represents anything but a poor marker. He's treating race as self-identified ethnic group with a distinctive set of traits, and a very large number of such groups share similar skin color.

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Replies to this message:
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