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Author | Topic: Human Races | |||||||||||||||||||||||
Peter Member (Idle past 1478 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
Isn't it likely that light skin was selected for in
low-sunlight regions because darker skin reduces (in the sense that you need more light to do it) Vit-D synthesis ? Otherwise the 'western europeans' would range in skin toneacross the ful spectrum rather than in the lighter end, surely. [This message has been edited by Peter, 12-05-2003]
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Peter Member (Idle past 1478 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: This implies that regionally associated, heritable traitsjust emerge at random, and leads to the populations originating in different regions came into being independently of one another. Genetic evidence points to a migration from Africa coupled withsome populational bottle-necks. If the population that headed out-of-Africa where a single populationthen according to what has been suggested in this thread they would be pretty homogenous. That populations in different regions are observabley differentand these differences are heritable means that something promoted particular phenotypes in the different regions. The different phenotypes are suggestive of a divergence amongstthe original migrant population. quote: Are you saying that the ToE's dependence on differentiationwithin a species depends on the above, or whether it happens or not depends on the above. Some researchers are suggesting that the emergence of modernhumans and apes did not occur as a distinct split, but was generated over time from an inter-breeding population with increasing degrees of differentiation. quote: Inuit are genetically pre-disposed to obesity (i.e. fat deposition)which is beneficial in a cold climate, and require less calcium in their diets (recommended calcium levels given to Inuit children can cause hypercalciuria at significantly higher rates than seen in non-inuit). They also possess lower incidence of genes associated with cardio-vascular disorders, which is beneficial if you want to survive longer with higher body-mass-index. quote: Agreed, although they have no name for themselves (or none thatthey are willing to divulge), but have come to accept the term (somewhat). The intrusion of Bantu herders into their hunter-gathering lifestylepre-dates western interaction with the region, but is not overly indicative of inter-breeding between the two different tribal cultures. There is some suggestion that all click-language speakers arerelated. http://www.marylandresearch.umd.edu/issues/fall2003/dna.html has: "The connection between populations who speak a click language, the language spoken by the Africans in the film "The Gods Must Be Crazy." The DNA shows that different peoples who use click language but live hundreds of miles apart, may be related. Says Tishkoff, "We have been able to show, for the first time, that the Sandawe of East Africa and bushmen from the south of Africa and the southern bushmen of Botswana, Namibia and South Africa share a recent common ancestry, within about 35,000 years. We speculate the southern bushmen originated in East Africa, and that they both are remnants of a very old group of hunter-gatherers, perhaps the earliest ancestors of modern humans." Which admittedly doesn't say anything about, well, anything in detailbut indicates that there is a genetic means of identifying 'Bushmen'. As for the celts --- well OK, even during the time of the RomanEmpire that was a bit tenuous (and I was thinking of Wales ). Interestingly there is a review onhttp://www.2think.org/cavalli-sforza.shtml which is a little schizophrenic. It states that "The variation among individuals is much greater than the differences among groups. In fact, the diversity among individuals is so enormous that the whole concept of race becomes meaningless at the genetic level", but just prior to that says "once the genes for surface traits such as coloration and stature are discounted". So once we discount the genes for the traits upon which racialdistinctions are usually made, suprisingly, we find no genetic evidence for race. Does that not seem a little, well, odd. Other selected quotes are :-"What the eye sees as racial differences - between Europeans and Africans, for example - are mainly adaptations to climate as humans moved from one continent to another. " "Those findings, plus the great genetic distance between present-day Africans and non-Africans, indicate that the split from the African branch is the oldest on the human family tree" "All Europeans are thought to be a hybrid population, with 65% Asian and 35% African genes" You cannot have it both ways ... there are either geneticallyobservable differences that allow us to trace humanity's origins back to Africa, or there are no significant differences between races that can be seen in the genome.
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
quote: I was arguing this point with Peter earlier in the thread but he claims that he is unconvinced and that one can place a clear boundary on one race and another. If you have a distribution of allele frequencies or a normal distribution of pairwise sequence differences for say a neutral locus like a microsatellite or the Dloop ...where in that distribution can one identify specific "races"? I fail to see it.
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sfs Member (Idle past 2533 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:More likely? Yes, I'd say so. But I don't see that it's certain. All northern peoples have straight hair, as far as I know -- would you argue that that must be the result of selection, since without selection they'd show the full range of hair shapes?
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sfs Member (Idle past 2533 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:It's certainly true that many regionally associated, heritable traits emerge at random. Remember all of those nonfunctional genetic markers we were talking about? They're all heritable traits that emerged at random; many of them are regionally associated. A random trait is unlikely to be associated only with one region (assuming we're talking about fairly small regions, as you have been) and also to be very common in that region -- that would suggest either selection or an extreme bottleneck. But there aren't very many traits (that I know of) that fit that description. quote:I don't know what you mean here. quote:Different populations still are pretty homogeneous, compared to other species; since we're dealing with our own species, we're attuned to picking out fairly minor differences. There's nothing that says heritable differences between the populations have to be the result of selection. Widely separated populations are pretty isolated genetically (until recently), and there has clearly been a significant amount of genetic drift, especially in all non-African populations. To a good approximation, populations in western Europe and eastern Asia each carry subsets of the alleles that left Africa; they just carry somewhat different subsets. Because of drift, populations will differ in their neutral variants. A signature of selection would be if in a particular trait two populations differed much more than they do on average over the rest of the genome, especially if there is independent evidence that the different phenotypes have selective advantage in the two populations. Skin color is in this category, as is lactase persistence and sickle cell trait. None of those traits is characteristic of a particular race, however, as you have defined race, and two of them aren't visible characteristics.
quote:I'm saying that in evolutionary theory, the genetic distance between populations depends on the time since they separated and the amount of gene flow since. Depending on those parameters, the distance can vary from almost zero to a whole bunch. quote:Are they more pre-disposed to obesity than many other populations, especially ones that are traditionally hunter-gatherers? Many populations are predisposed to obesity and diabetes. I'd say it's at least as likely that this is the ancestral human phenotype, and that the phenotype we often define as normal arose only in a few populations (probably agricultural ones). quote:Plausible. Is there good evidence for this, though? All I can find is a single report in CMAJ that is pretty scanty evidence. (See Low-calcium diet | CMAJ.) I wouldn't be surprised if it were true, however. As I said, the Inuit are a group in which I might expect to see some distinctive selected alleles. quote:I don't think there's any evidence at all for this one. If anything, the evidence is to the contrary: "Specifically, compared to whites, both Oji-Cree and Inuit have an excess of 'deleterious alleles' from 12 candidate genes in atherosclerosis and/or diabetes." (Clin Chim Acta. 1999 Aug;286(1-2):47-61). Inuit are thought to have less cardiovasular disease (although even that is in some dispute -- see "Low incidence of cardiovascular disease among the Inuit--what is the evidence?" Atherosclerosis. 2003 Feb;166(2):351-7), but they also tradionally have a diet high in fish oil, which is thought to be protective against cardiovascular disease. quote:No, but the genetic date are pretty clear: "The data of Soodyall (1993) indicate that the Dama similarly have only ~5% Khoisan lineages but that the southern African Xhosa and Zulu may have ~25% and ~50% Khoisan lineages, respectively (also all L1d). This much higher level of assimilation is consistent with the presence of Khoisan click consonants in both languages. In southern Africa, Khoisan speakers themselves appear to have experienced high levels of assimilation of Bantu lineages: ~23% in the Vasikela !Kung (Chen et al. 2000), ~24% in the Sekele !Kung (Soodyall 1993), and ~61% in the Khwe, consistent with their similar physical appearance to southern African Bantu speakers (Chen et al. 2000)." That's from a paper on mitochondrial DNA; Y chromosome data shows a similar pattern. (References on request.) I have to go to bed now -- lot's of snow shoveling to do tomorrow. I'll write more if I have time.
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sfs Member (Idle past 2533 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:If Cavalli-Sforza has evidence that these traits, apart from skin color, are the result of adaptations to climate, he should tell the rest of us. quote:No one has denied that there are genetically observable differences between populations. What we deny is that there are sets of differences that line up well enough with culturally defined races or ethnic groups to justify talking about those groups having a basis in genetics. Here's the genetic situation as I understand it. Human groups do differ genetically, on every scale that you can examine. It's trivial to distinguish between a West African and a northern European, or a Mayan and a Tamil, based on their chromosomes, for example. It gets harder to distinguish groups as they get closer geographically and historically, but it is still possible. You can distinguish African from non-Africans. You can distinguish groups from different parts of the same continent, or groups from different language families, or neighboring tribes; you can very likely distinguish neighboring villages. Some of the genetic differences are the result of natural selection, either because they represent different genetic responses to the same pressure or because selective pressures are different in different environments (including in different cultural environments). Some of it is purely random. How much phenotypic difference falls into either category is not known at present. There is almost never a clear boundary between different genotypes, but rather a slow change over distance, with different genes varying at different rates and in different geographic regions. Culturally defined groups are (or were, at least) usually confined to some geographic region, so cultural groups inevitably correlate with certain genotypes. That does not, by itself, make the cultural groups a natural way of dividing the genotypic variation; any arbitrarily assigned geographic boundaries would also show a correlation. Some (but not all) culturally defined groups do, in addition, show a higher degree of relatedness within them than a randomly assigned geographical group would; i.e. they are somewhat inbred. This is a fairly small effect for humans, since we are a highly outbred species. Populations for which it is significant tend to be small, isolated recent hunter-gatherer groups. These groups probably come closest to what you mean by races, but they generally don't have the kind of obvious distinctive physical characteristics that would be used as race markers. Many other groups are outbred enough that they aren't usefully thought of as a genetic subpopulation, and some groups are (genetically speaking) a hodge-podge of different ancestries. Overall, then, culturally defined groups are at best a very imprecise reflection of patterns of genetic variation. Even with its imprecision, group identity can still be useful: physicians will sometimes use self-identified ethnicity as a clue to guide diagnosis or treatment. That's rational, but it's a weak source of information and can easily be wrong, not just about individuals but about entire communities. None of this is to say that political/social considerations never obscure genetic realities. There are people involved in genetics (especially among those that worry about ethical and social aspects of genetics) who adopt an extreme rejection of genetic differences between human populations. For example, the International Haplotype Map Project is currently planning to map haplotypes in three populations, one African, one Asian and one European; the hope is to add more later if they prove to be needed. For those who planned this strategy, the justification for it is simple: different populations have somewhat different sets of haplotypes, and if the map is going to be medically useful for most of the world's people (which is its goal), it has to provide maps for different populations. (Fortunately, haplotypes only vary a lot on large geographic scales, so a small number of populations should be enough to describe common haplotypes for most people.) For some of the ethics people, however, the strategy amounts to the "racialization" of genetics, and is something to be condemned. I think such reactions are quite confused, but they do occur. Most working human geneticists don't react that way, however. On the other hand, they do tend to be aware that when they talk, they're talking about people, and that people (other than other geneticists) may well be listening. They therefore choose their words with care. Couching any kind of statement about human genetics in terms of the word "race" pretty much guarantees that it will be misunderstood, and that by itself an excellent reason for avoiding it. Now, if you will excuse me, I have to go finish writing a short talk in which I will explain to the steering committee of the HapMap why they should choose markers in Africans and not in Europeans.
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Peter Member (Idle past 1478 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: It's actually an issue that I find somewhat confusing. I assume by 'curly hair' you mean the very tight curls associatedmost often with those of African or Afro-Carribean descent, rather than the 'naturally curly hair' of Charlie Brown's would-=be girlfriend. But eye colour also is a problem for me. From people I know with mixed-raced parents, they all seem to havethe dark eyes and tight curls of that side of the family. If that is the case all of the time it would suggest that the genetic controlling this feature are dominant (blue eyes are a recessive feature I believe). Why have recessive features become dominant in somepopulations? How could that happen with significantly inter-breeding gloal populations?
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Peter Member (Idle past 1478 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
What you have said perturbs me.
There is a suggestion that because somethingexists in a continuum we must negelect differences between 'items' in two different points of the continuum ... like red-light is just electromagnetics isn't it, no different from UV or X-rays. If the polarised objection to a genetic basis for race ispolitically motivated, then it is as objectionalble as using race for political ends, or promoting creation science in schools. All of the citations show that differentiating between differentcultural members IS possible at the level of the genome. Even with the inter-breeding between Zulu, Bantu, and Khosian people, from fairly narrow geographic ranges. How can one posit differences between different culturallydivided groups as evidence against race? There are objectionable associations with racial determination,and I cannot see any reason that racial differentiation should matter on a day-to-day personal basis. It has interest in tracing human origins, perhaps. My problem in this thread is not that I want there to beracial distinctions, but that I feel that denial of them is driven by politics and not by scientific inquiry.
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
quote: Where do you get this from sfs or my posts? from sfs post quote: That you can replace cultural groups with any arbitrary geographical demarcation is the reason race is a useless concept. This is not some political game. In order for "race" to be a useful concept genetically it would have to be supported in such a way that you could not replace "races" with almost any arbitrary grouping. This is the case because of the heavy outbreeding of humans coupled with a normal distribution of genetic variation rather than blunt genetic differentiation among populations that one could consider "races". It is no more a ducking of the political issues to avoid using the term race which is not supported by genetics and is a word that has had multiple historical meanings than it is to call avoid calling genetics "blended inheritance".
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sfs Member (Idle past 2533 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:The problem is that you can make many other equally valid divisions. A Khoisan-speaking village may be closer genetically to the Bantu-speaking village next door than it is to the Khoisan-speaking village 50 miles away, but you would label the two Khoisan-speaking villages as part of the same race and the Bantu-speaking village a different race. When you do that, you demonstrate that your labels are cultural, not biological. It's not that the cultural labels never correlate with genetic relatedness; they often do -- on average, Khoisan speakers are more closely related to each other than they are to Bantu speakers. But that correlation does not mean that the cultural label is itself a genetic description. When you treat the label as if it were a biological description, which is what you're doing, you're are led into ways of thinking that may be quite mistaken. Language influences how we think, and in this case it is my professional opinion that the language you're advocating make thought less precise and more error-prone. Instead of race, think about people who live in the same city. Inhabitants of a given city are, on average, more closely related to each other than they are to people living elsewhere. Do you think it therefore makes sense to talk about a "biological basis" of place of residence? Saying someone is a Dubliner may well convey more genetic information than saying he's Irish, but the latter description automatically makes us think that it's saying something more fundamental about the person's makeup than the former. Even for geneticists who know all the caveats it's very easy to fall into essentialist thinking about groups, and be misled in the process. Using racial language only makes the problem worse.
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Too Tired Inactive Member |
Mammathus writes:
---------I don't deny that populations have diverged. I don't even deny that some populations may have private polymorphisms, little gene flow, etc. But to ascribe these differences to a level "race" that has biologically been ascribed to a sub-species level distinction is preposterous. --------- I've never understood why so many people think that 'races' in the human species should be qualitatively different from 'subspecies' in other animals. They're both generally fuzzy categories and both traditionally based on more-or-less consistent observable morphological differences. I've looked at the genetics of both categories and there's not much difference there, either. See my not-very-well-written paper, "The Race FAQ" at Just a moment... and at least read my critique of Templeton's 1998 paper on race at the end. Also there's some interesting stuff from Klein & Takahata, Cavalli-Sforza in his pre-race-denial days, Sewall Wright and others. Cheers, John
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
Hi John
While your Faq is actually quite well written, you are basically advocating a re-assignment of the word "race" (and sub-species from your article) with various other terms such as phylogeographical subspecies. At the same time you admit that cultural definitions of race are not accurate quote: I am not taking issue with your article and not trying to politicize the debate. However, I am of the same opinion as sfs that when you have such a fuzzy concept as "race" that does not necessarily correlate with the genetics of a species, just renaming your terms arbitrarily serves no purpose. If as sfs pointed out, that Dubliner is a more accurate measure of genetic relatedness than Irish what use is race in forensics or medicine? The Dublin race? The Bronx race? There are issues of the utility of the concept in general that probably requires the development of new terms rather than mis applying old terms that have a fairly political history. Why did Avise et al. bother with phylogeographical subspecies? This in not an old term. They developed a novel term and they were not specifically dealing with human variation. Why just rename "race" and confuse everybody even further when from a scientific perspective, one would wish to have clarity?
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Peter Member (Idle past 1478 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: Sorry if I implied that it was your (or SFS's) motivation,not intentional there. My concern is that there is a great push for there beingno genetic basis for race which doesnt seem to tie up with what the people who are claiming that are saying elsewhere in the same papers. If there is no race, how CAN you tell that there are differencesin genomes between African and non-Africans, or that Australian aborigines are not closely related to modern indigenous Africans. You cannot make ANY arbitrary geographical demarcation and finda genetic correlation. To take an example from sfs's reply to the same post that you are replying to) look at a city. Say Dublin, or London, or Paris. There is NO genetic marker available for such a populationbecause there is a very wide range of lineages that originate in different geographioc locations. Likewise if the geographic area is too large, or divided by geological barriers this will not be the case.
quote: You cannot replace 'race' with 'almost any arbitrary grouping' unlessI am mis-understanding your use of arbitrary. Take a city population and study their genetic diversity andit will be all over the map. Sub-divide the same group based upon assumed racial origin and you'll start to see correlations. If this were not the case genetic distance would not correlateto geographic distance. Perhaps my use of the word divergence is a little strong,but there is diversification. If you accpet that the genetic evidence points to an out-of-africa origin, then you have to accept diversification. That diversity is forged geographically, and most concepts of'race' correlate with geographical origin.
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Peter Member (Idle past 1478 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: No, you demonstrate that neither the Bantu-speeaking not Khosianspeaking villages are representative of the races in question. The history of this relationship, in terms of inter-tribalmarriages, changes the situation. The genetic distance between one Khosian speaking villageand another (assuming one is relatively isolated) provides a measure of 'out breeding'.
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
quote: There are differences in the genome between mother and child. There are enormous among African genetic differences so who are you going to pick as your "African" race as a standard to which to compare to other non-Africans? How is this lumping of divergent groups of people who may differ from one another more than the groups you are comparing them to going to guide research into the effects of novel drugs on humans? forensics? Anything? How about as these groups outbreed? How do you classify the descendants who may be genetically a mish mash of dozens of different "races"?
quote: If according to you, one can designate "original lineages" despite massive interbreeding in say London or anywhere else then there should be absolutely no correlation between genetic distance and geographic distance...one should always statically maintain one's race just like a separate species.
quote: First off, I don't necessarily think OOA (in the form of purist supporters) is correct but in any event, I can accept diversification without subscribing to the cultural concept of "race".
quote: Oh really? Your own personal definitions of race in this thread have varied from as extreme as African, Asian, Caucasian to 3 individuals composing a potential "race". Compound how variable your definitions of race are with the other variant defintions of race on top of the changes throughout the history of the word itself and you are left with a term that is almost as ill defined as "creationist kinds".
quote: Oh really? And this does not apply EVERYWHERE else? Show me a place where you do not have large numbers of lineages orginating from different locations even in relatively isolated populations. Sfs point that the chance that even in a city, your chances of being related to others from the city are higher than another city kinda throws the "race" concept for a loop. A person from Munich has a higher chance of being related to other people from Munich than from Berlin...Munich race? (aside from the fact that some of them seem to think so) Why is it any less valid to you to have "identity by residence" than race? You can find genetic relationships that correlate just as weakly as anything culturally you have proposed so why not just lump people by zip code under this scenario?
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