Freethought & Rationalism Archive

Doubting Didymus · 12-17-2002, 03:14 PM

Quote:

Originally posted by pz:

Do you think that genes could have nothing at all to do with morphology, or something?

What? I don't understand how you came to ask this question.

I still maintain that heritable factors must have genetic roots, but that is another question entirely.

RufusAtticus · 12-17-2002, 06:07 PM

Quote:

Originally posted by Doubting Didymus:
How very interesting. So, may nose shape change as a consequence of mutations in the parts of these genes that influence other features? Or is that too much of an extrapolation?

Yes and no. Pz is talking about pleiotropic genes. (Genes that influence more than one trait.) In such genes sometimes a mutation will only effect one or some of the traits influenced by the gene. Other times it will not.

Furthermore, pz is pointing out that morphological features are usually "quantative traits" and the genes that influence them are many and they have small effects.

~~RvFvS~~

pz · 12-17-2002, 06:29 PM

Quote:

Originally posted by RufusAtticus:
Yes and no. Pz is talking about pleiotropic genes. (Genes that influence more than one trait.)

I would also add that almost all (or all?) genes are pleiotropic, and that especially if you are talking about developmentally significant genes, the interactions are particularly complex.

I suspect that if you traced back every gene that contributed to the shape of your nose, you'd find that it pretty much included the entire genome.

echidna · 12-17-2002, 06:56 PM

[No understanding of genetics]

But given that a range of physical characteristics may represent commonly recognised racial traits, surely then it must be possible to statistically group the underlying genetic influences for these characteristics. Complex yes given the interactions, but surely possible in theory.

10 markers for instance seems to be a very narrow X-section to conduct any meaningful study.

If a complex combination (even if very complex) of pleiotropic genes gives rise to flat noses, straight black hair, narrower eyes, then surely it is theoretically possible (even if more difficult than our understanding allows us today) to map these and others, statistically as markers for Asian features for instance (half Chinese myself).

[/No understanding of genetics]

Quote:

The idea of race is not reflected in a person's genes, Brazilian researchers said, confirming what scientists have long said -- that race has no meaning genetically.

To the layman this strikes me as very PC rather than accurate. I still fail to understand how from their study they can conclude that no cosmetically-based definition of race (especially statistically based) can genetically exist.

Of course how those cosmetic differences might or might NOT relate to other characteristics such as behavioural is entirely another discussion.

ps418 · 12-18-2002, 01:04 PM

Quote:

Originally posted by echidna:
To the layman this strikes me as very PC rather than accurate. I still fail to understand how from their study they can conclude that no cosmetically-based definition of race (especially statistically based) can genetically exist.

I'm a genetic layman too. But after reading the Genome Biology article above (Risch et al 2002), it would appear to be somewhat of an overstatement to say that race is a biologically or genetically meaningless concept.

Quote:

Because of the large amount of variation observed within races versus between races, some commentators have denied genetic differentiation between the races; for example, �Genetic data � show that any two individuals within a particular population are as different genetically as any two people selected from any two populations in the world.� [18]. This assertion is both counter-intuitive and factually incorrect [12,13]. If it were true, it would be impossible to create discrete clusters of humans (that end up corre-sponding to the major races), for example as was done by Wilson et al. [2], with even as few as 20 randomly chosen genetic markers. Two Caucasians are more similar to each other genetically than a Caucasian and an Asian

. . . recent SNP surveys of the different races have shown that lower frequency variants are much more likely to be specific to a single race or shared by only two races than are common variants [12,19-20]. In one study, only 21% of 3,899 SNPswere found to be pan-ethnic, and some race-specific SNPs were found to have a frequency greater than 25% [12].(p. 5)

Quote:

The results are the same irrespective of the type of genetic markers employed, be they classical systems [5], restriction fragment length polymorphisms (R LPs) [6], microsatellites [7-11], or single nucleotide polymorphisms (SNPs) [12]. For example, studying 14 indigenous populations from 5 continents with 30 microsatellite loci, Bowcock et al. [7] observed that the 14 populations clustered into the five continental groups, as depicted in igure 1. . . The identical diagram has since been derived by others, using a similar or greater number of microsatellite markers and individuals [8,9]. More recently, a survey of 3,899 SNPs in 313 genes based on US populations (Caucasians, African-Americans, Asians and Hispanics) once again provided distinct and non-overlapping clustering of the Caucasian, African-American and Asian samples [12]: "The results confirmed the integrity of the self-described ancestry of these individuals�. Hispanics, who represent a recently admixed group between Native American, Caucasian and African, did not form a distinct subgroup, but clustered variously with the other groups. A previous cluster analysis based on a much smaller number of SNPs led to a similar conclusion: A tree relating 144 individuals from 12 human groups of Africa, Asia, Europe and Oceania, inferred from an average of 75 DNA polymorphisms/individual, is remarkable in that most individuals cluster with other members of their regional group� [13]. Effectively, these population genetic studies have recapitulated the classical definition of races based on continental ancestry - namely African, Caucasian (Europe and Middle East), Asian, Pacific Islander (for example, Australian, New Guinean and Melanesian), and Native American (p. 4-5)

Quote:

If biological is defined as genetic then, as detailed above, a decade or more of population genetics research has documented genetic, and therefore biological, differentiation among the races. This conclusion was most recently reinforced by the analysis of Wilson et al. [2]. If biological is defined by susceptibility to, and natural history of, a chronic disease, then again numerous studies over past decades have documented biological differences among the races. In this context, it is difficult to imagine that such differences are not meaningful. Indeed, it is difficult to conceive of a definition of �biological� that does not lead to racial differentiation, except perhaps one as extreme as speciation.

. . . the various racial groups were easily distinguishable on the basis of even a modest number of random genetic markers; furthermore, categorization is extremely resistant to variation according to the type of markers used (for example, RLPs, microsatellites or SNPs).

. . . it would be difficult to distinguish most Caucasians and Asians on the basis of skin pigment alone, yet they are easily distinguished by genetic markers.

bluefugue · 12-18-2002, 01:20 PM

Speaking as a complete layman, I have always assumed that, at least in part, the characteristics we described in various "races" came about because of geographical isolation in prehistoric times and marked the division (or the prelude to a division) of humans into subspecies. What I mean is, for a long time, Africans and Asians and Europeans (for instance) were relatively isolated from one another and so different characteristics (among which are skin color, hair color, eyelid shape, bone structure, etc.) developed in the various groups. Had this geographical isolation continued for many more thousands of years, it might have led to reproductive isolation and the splitting of h. sapiens into more than one species.

Is this completely off base? It always seemed transparently obvious to me, but of course the "obvious" is not always correect.

As to another point that has been raised, it's true that an Irishman and an African may share curly hair, but in a "common sense" way I would assume that a (full-blooded) Irishman shares a more recent ancestor with other Europeans than he shares with a full-blooded native of the Congo. I'm aware there are dangerous pitfalls here (what exactly is an "Irishman," how is it defined, etc.), but in a general sense is this completely off base?

ps418 · 12-18-2002, 02:06 PM

Quote:

Originally posted by bluefugue:


I must confess I find this article puzzling. Is it suggesting there is no correlation between things like hair color, skin color, bone structure, etc., and genes? Are we to suppose that the cosmetic differences between an Irishman and an Australian Aborigine are culturally determined? Or is it asserting that interbreeding has mixed up the genes so much that it's impossible to disentangle them at this point... or what *is* it saying?

What the research in question shows is not that "race is not reflected in genes," as the title of this thread suggests, but only that "in Brazil as a whole, color is a weak predictor of African ancestry." The CNN article, on the other hand, says something far different:

Quote:

The Brazilian researchers looked at one of the most racially mixed populations in the world for their study, which found there is no way to look at someone's genes and determine his or her race.

That is not a conclusion that could be justified, even in theory, by the experimental design described in the CNN article. Plus, it would seem to contradict the research cited in Risch et al.s paper. Risch et al also talk about how skin color and how predictive it is of ancestry:

Quote:

Genetic differentiation among the races has also led to somevariation in pigmentation across races, but considerable variation within races remains, and there is substantial overlap for this feature. For example, it would be difficult to distinguish most Caucasians and Asians on the basis of skin pigment alone, yet they are easily distinguished by genetic markers

[ December 18, 2002: Message edited by: ps418 ]

bluefugue · 12-18-2002, 02:17 PM

So in other words, journalism adds some static, as usual.

echidna · 12-18-2002, 02:27 PM

Slightly offtopic : Patrick I glanced at this morning�s Herald-Sun. Front page picture is 2 quite attractive identical twin sisters who just received their VCE (A-levels) results. Identical scores 99.95 ! Some of their individual marks were different, but I couldn�t help remembering ...

Vorkosigan · 12-18-2002, 08:15 PM

For example, it would be difficult to distinguish most Caucasians and Asians on the basis of skin pigment alone, yet they are easily distinguished by genetic markers

LOL. Just yesterday I shocked my fourth year students when they all claimed I was lighter than they were, and after comparison, it was obvious to the naked eye that caucasian Michael was the darkest person in the classroom!

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12-18-2002, 01:20 PM	#26
bluefugue Veteran Member Join Date: Aug 2001 Location: Los Angeles Posts: 1,427	Speaking as a complete layman, I have always assumed that, at least in part, the characteristics we described in various "races" came about because of geographical isolation in prehistoric times and marked the division (or the prelude to a division) of humans into subspecies. What I mean is, for a long time, Africans and Asians and Europeans (for instance) were relatively isolated from one another and so different characteristics (among which are skin color, hair color, eyelid shape, bone structure, etc.) developed in the various groups. Had this geographical isolation continued for many more thousands of years, it might have led to reproductive isolation and the splitting of h. sapiens into more than one species. Is this completely off base? It always seemed transparently obvious to me, but of course the "obvious" is not always correect. As to another point that has been raised, it's true that an Irishman and an African may share curly hair, but in a "common sense" way I would assume that a (full-blooded) Irishman shares a more recent ancestor with other Europeans than he shares with a full-blooded native of the Congo. I'm aware there are dangerous pitfalls here (what exactly is an "Irishman," how is it defined, etc.), but in a general sense is this completely off base?

12-18-2002, 02:17 PM	#28
bluefugue Veteran Member Join Date: Aug 2001 Location: Los Angeles Posts: 1,427	So in other words, journalism adds some static, as usual.

12-18-2002, 02:27 PM	#29
echidna Veteran Member Join Date: May 2001 Location: Melbourne, Australia Posts: 2,832	Slightly offtopic : Patrick I glanced at this morning�s Herald-Sun. Front page picture is 2 quite attractive identical twin sisters who just received their VCE (A-levels) results. Identical scores 99.95 ! Some of their individual marks were different, but I couldn�t help remembering ...

12-18-2002, 08:15 PM	#30
Vorkosigan Contributor Join Date: Jan 2001 Location: Barrayar Posts: 11,866	For example, it would be difficult to distinguish most Caucasians and Asians on the basis of skin pigment alone, yet they are easily distinguished by genetic markers LOL. Just yesterday I shocked my fourth year students when they all claimed I was lighter than they were, and after comparison, it was obvious to the naked eye that caucasian Michael was the darkest person in the classroom!

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