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Author | Topic: Human Races | |||||||||||||||||||||||||||
sfs Member (Idle past 2553 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:I don't have any real opinion on whether human population structure is unusual or not. I'm just of the opinion that use of the term "race" for anything biological about humans at this point produces more confusion and less communication than any possible gain it brings. quote:Interesting material, especially that comparing human variation with other species. Much of that is new to me, since I don't know much about non-human genetics (having somehow neglected to take a course in genetics at any point in my schooling). One thing that make me scratch my head, though: it's becoming clear from autosomal SNP data (vast quantities of autosomal SNP data) that chimps really do have at least twice the diversity of humans -- but this rather significant difference doesn't show up at all in the tables. No doubt (as usual) more data will clarify the situation. I think there are a few distinctions that you slide over too quickly, however, for a FAQ that's addressing the question of race in humans. You treat folk definitions, anthropological definitions and genetic definitions of human races as if they were interchangeable. They're not. In the U.S., folk definitions of races are such that any detectable amount of African ancestry makes a person "black". Since such a person may be genetically and morphologically more similar to the average European, this means that the folk category does not align well with any biological category. This may not matter much if you're interested only in whether humans can be described as having subspecies, but it matters a heck of a lot if you actually want to use race as a category in the real world. Similarly, anthropological definitions are not the same as genetic ones. "Sub-saharan African" is not one of the traditional, widely used racial categories; "Negroid" is. The latter category includes Africans, Filipinos, Andaman Islanders, and Melanesians, groups that don't form any kind of meaningful genetic cluster. Using racial terminology again serves only to confuse things, for no obvious purpose. There's a more subtle problem in the use of "clade" (and not just by you). Despite Nei and Roychudhury's language, you can't really form a phylogenetic tree for human populations, or for any interbreeding diploid populations; or rather, you can't form a unique, non-reticulating tree. Genes have phylogenetic trees; populations form webs. For many purposes a phylogenetic tree is a reasonable approximation, but when one uses it it's easy to forget that it is only an approximation, and that the population you're talking about may be an average that doesn't correspond to any actual individuals. I point this out mostly because talking about Africans as a clade bugs me. It seems very likely that the Out of Africa migration(s) came from a source population in East Africa, much of which remained in Africa; their descendents are still there. If you're thinking in terms of phylogenetic trees, that branch together with the rest of the African population do not form a clade; rather, the East Africans form a clade with the rest of the world's populations. When you cluster people by gene frequency, however, you will find that the East Africans' descendents within Africa do form a "clade" (a cluster, really) with other Africans, at least at most loci, thanks to continuing gene flow within Africa.
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sfs Member (Idle past 2553 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:In this case, probably a secondary result of selection for lighter skin.
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sfs Member (Idle past 2553 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:So if the Khoisan "race" consists of twenty villages, each situated near a different Bantu-speaking village, which village is representative of the race? It's quite possible for each of the 20 villages to be closer genetically to its immediate neighbor than to any of the other Khoisan-speaking villages, and for the 20 groups still to share a common cultural identity and distinctive genetic and phenotypic traits (all of which they would share to some extent with other Khoisan populations). By your definition they're a race, but by your argument here, it's a race without any representatives. And while this is an extreme case, it is an extreme case of the normal situation in human genetics.
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sfs Member (Idle past 2553 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:I chose my analogy fairly carefully. Cities vary in their composition. Some, like London, are highly cosmopolitan, with genetic input from many sources. Others, like, I don't know, Lagos maybe, or Osaka, draw their population primarily from one region; such cities will share all of the genetic characteristics of their region, and will also have their own (quite faint) distinctive genetic signature because of inbreeding within the city boundaries. Both kinds of city are analogous to culturally defined ethnic groups, some of which have highly heterogenous composition and some of which don't. quote:Look again at what you just wrote. Genetic distance correlates with geographic distance. Cities are compact geographically. What conclusion can you therefore draw about genetic distances within a city?
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Too Tired Inactive Member |
Mammathus writes:
quote: Thanks, I appreciate the compliment.
quote: I didn't really say that cultural definitions of race are inaccurate, but I don't know exactly what you mean by "accurate" so I won't pursue it right now. Looking at the phylogeographic subspecies definition isn't so much a matter of advocating a reassignment of terms, it's an attempt to get a definition on the table that has the blessing of some prominent biologists in the field of non-human taxonomy (John C. Avise, Stephen J. O'Brien, Ernst Mayr, EO Wilson et al.) so that the subspecies synonym "race" which we use for humans might be given some guidelines. So much of the race debate is about how to define race in the first place, with endless silly arguments about the 'Dubliner race', the 'Bronx race', the green-eyed race, etc etc. The phylogeographic subspecies concept was developed to ensure that those populations called 'subspecies' are evolutionarily significant segments of a species. Its use still requires the sound judgement of biologists, and the subspecies level of taxonomy is and will always be fuzzy practically by definition, but it's still a big improvement over the way subspecies have too often been assigned in the past. In the studies I've read that employ this definition, many or even most of the classical subspecies don't meet the criteria, in other words it's a lot tougher to be named a subspecies under this definition than under the older definitions of the term. Phylogeographic subspecies are more distinct species segments than classical subspecies, which in many cases weren't very distinct at all. What's the relevance to the race debate? Well, there's recent population genetic data on these phylogeographic subspecies that can be compared to population genetic data for humans. That allows us to assess the claim that we hear so often about how human populations are NOTHING like subspecies. As it turns outs, some human populations are an AWFUL LOT like subspecies, in terms of morphology AND in terms of genetic population structure. To my way of thinking, that's highly relevant to the race question, in fact it answers the question. The rest is just squabbling over details, which is all well and good but is quite apart from debating whether or not human races exist. John
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NosyNed Member Posts: 9003 From: Canada Joined: |
Check this months issue of Scientific American.
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Too Tired Inactive Member |
SFS writes:
quote: When I wrote the paper, autosomal microsatellites were the marker of choice and about the only option for comparing a dozen or more species. I know that chimps have more SNP diversity than humans, but I think it's illuminating to look at as many species as possible to get a sense of how humans rank, and comparable SNP data wasn't available. In terms of population structure (how the diversity is partitioned) I have a second-hand reference (the original was in an unpublished doctor's thesis) to an Fst value of .02 between I believe P.t.troglodytes and P.t.vellerosus, two supposed subspecies yet quite a bit less distinct than most human groups, according to this data. But there hasn't been a good comprehensive study of wild chimp population structure done using autosomal markers, it's all been mtDNA which is a single locus and not wholly reliable.
quote: To be honest it's not an aspect of the debate that interests me. Supposedly there's all this confusion over what race means to the man on the street or the college freshman or whomever. It's not something I've encountered but I'm not in a position to know if it's out there or not. (The one thing I've noticed is that people who argue against human races tend to think of race as a synonym for species.) The issues of hypodescent and admixture certainly have their place but they don't have much bearing on the race question as I see it. I mean, do you actually know somebody who would consider a European-looking person black because he or she had 1% African ancestry? Maybe you do, but just because a term or concept can't be idiot-proofed doesn't mean it has to be discarded. John
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Mammuthus Member (Idle past 6495 days) Posts: 3085 From: Munich, Germany Joined: |
Hi TT,
quote: This is where some of my problem with this concept stems. To call phylogeographical subspecies the equivalent of "race" in humans amplfies the significance of the diversity among human populations while minimizing those in other species. Look at some of the groups O'Brien for example, has examined such as a group I have worked with, proboscidians. Forest elephants, Loxodonta cyclotis, were given a sub-species/species designation based on a level of divergence far more pronounced than that which exists between human populations Science. 2001 Aug 24;293(5534):1473-7. Related Articles, Links Comment in:Science. 2001 Aug 24;293(5534):1414. Genetic evidence for two species of elephant in Africa. Roca AL, Georgiadis N, Pecon-Slattery J, O'Brien SJ. Laboratory of Genomic Diversity, National Cancer Institute, Frederick, MD 21702, USA. Elephants from the tropical forests of Africa are morphologically distinct from savannah or bush elephants. Dart-biopsy samples from 195 free-ranging African elephants in 21 populations were examined for DNA sequence variation in four nuclear genes (1732 base pairs). Phylogenetic distinctions between African forest elephant and savannah elephant populations corresponded to 58% of the difference in the same genes between elephant genera Loxodonta (African) and Elephas (Asian). Large genetic distance, multiple genetically fixed nucleotide site differences, morphological and habitat distinctions, and extremely limited hybridization of gene flow between forest and savannah elephants support the recognition and conservation management of two African species: Loxodonta africana and Loxodonta cyclotis. These are two species that can and do interbreed where their ranges come in contact and until only a few years ago were thought to be all part of the same species. This is more in line with what O'Brien, Avise, etc. are trying to accomplish with the phylogeographic subspecies assignments. If one does the same with non-human primates and finds older and more diverse lineages in say, P. troglodytes than one finds in H. sapiens, how can one consider the divisions equivalent and cover them with the same definition? I don't think it is semantics. If evolution in one species is markedly different from related species, the terminology should reflect this difference i.e. there is no L. cyclotis version of humans. I would not take issue, after more data is collected, with rough subdivisions of human genetic diversty that analyzes multiple loci and is based in principle on relevant comparisons to non-human primates. However, even the phylogeographic subspecies concept does not overlap with a common or folk concept of race. One would have to redefine race scientifically and somehow hope that everyone from the general public to funding agencies to potential candidates for drug screens etc etc magically understands and acknowledges that science has changed the definition. It would be far easier and productive to use novel terminology or terminology used for other species to designate the differences than to use a term that is already in use and that has variable meanings both historically in science and in layman terms. I am not even necessarily opposed to phylogeographical subspecies per se. Only that in applying it to humans or any other species where the are less among group differences than say Loxodonta, the terminology reflects this so that one gets some biological meaning from the terms. Race does not do the trick.
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Peter Member (Idle past 1499 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: Those who, according to at least one of the papers referencedduring this discussion, share alleles that are not present in Europeans and Asians. There are aprrox. (without looking back) 20 of these.
quote: What has this to do with it? If you have a group of populations with no reproductive barrieryou can get highly embedded crosses, that doesn't mean that a concept of race is non-existent. I am not arguing that you won't get convergence with significantinter-breeding, I'm saying that that has not happened to a sufficient degree to claim that there is no biological basis for race. quote: This doesn't make sense, logically. If, in one region you have sufficient inter-breeding to comletelyobscure all traces of original lineages, then in that location you will have a new, unique trait-set, since the likelihood of haveing the exact same mix elsewhere would be very small. So the 'new' lineage would have a geographically traceable origin. If this has not happened sufficiently yet, then you would findtraces of the lineage origins in any case. You cannot start a lineage if you live on opposite sides ofthe world (unless you have an inter-national sperm/egg bank I suppose). quote: Not paying any attention to it and not 'subscribing' to it aredifferent. I doubt that there is a society anywhere that doesn't have an ingrained concept of race ... socially constructed yes, but there. If Out-Of-Africa is incorrect, then human populations emergedseparately in separate locations, and the diversification would be even more pronounced, since it would be older. quote: Well, yes. No matter how much vagueness there is in a concept of race,ultimately there is a geographic component. One doesn't think of the bloke up the steet as of a different race, unless he's different from all the usual residents ... and the only reason that someone would be that different are unfortunate circumstances of disease or other disability, or because they come from somewhere else ... or their family line comes from somewhere else. There are people in the US who think of themselves as Irish-American,or African-American ... almost all racial concepts have a geographic component (even Dubliners or Berliners). quote: Outside of the US, UK, and Australia pretty much all over. Western Europe has a large degree of inter-mingling, but lessso than the colonies ... but move to the Indian sub-continent or mainland Asia, or S.America (outside the large population centres) or Amongst the Native American tribes, or African tribes ... and the number of inputs will be MUCH less. quote: It's not invalid ... but that ISN'T biologically based. You seem to be suggesting that global inter-breeding has beencommon across the ages ... I've not seen historical evidence of this. Human societies have been fairly xenophobic, on the whole.
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Too Tired Inactive Member |
Mammathus writes:
quote: It could amplify or diminish your sense of human group diversity depending on what your original sense of it is. But in any case it at least gives an accurate view of our species diversity with respect to that found in other mammals.
quote: No, forest and savannah elephants were given SPECIES designations based on strong genetic distinctiveness which indicates very limited gene flow between the two. I have both the Roca et al. article and the Comstock et al. from Molecular Ecology, which I'm happy to email if anyone wants them. I might be misreading you, but it sounds like you're failing to make a crucial distinction between the terms 'subspecies' and 'species'. To my knowledge nobody in modern times is advocating the existence of different SPECIES within extant humans, so of course the level of genetic difference between these elephant species is much greater than what's found in humans. It's the SUBSPECIES level of taxonomy that's useful to examine for the race question in humans. Incidentally, the Comstock paper gives microsatellite Fst values of .07-.08 for the major geographic groups of the savannah species (L. africana), less distinct by this measure than the traditional human races, and so without some compelling morphological differences between them there probably will be no effort to name subspecies within savannah elephants.
quote: Again, no, in this case the genetics indicate a general lack of gene flow between forest and savannah elephants even when a population of one species is in closer proximity to the other species than to another population of its own. There's evidence of minor hybridization but not enough to threaten the genetic integrity of either species. This case puts you squarely into the biological species concept, and the phylogeographic subspecies concept doesn't enter into it.
quote: It happens all the time - that's taxonomy for you. Consider the Lake Victoria cichlids or Darwin's finches.(Just a moment...) There are full-blown species within these groups that have only formed in the past ten thousand years or so. These different species are nearly indistinguishable genetically and yet they're considered full species because they've evolved mechanisms that reproductively isolate them from other such species. They're clearly less distinct genetically than are the major human groups, but human groups are merely races because they freely (more-or-less) interbreed. So taxonomy at the lowest levels is really more about reproductive isolation than about length of separation. Race, subspecies, species - each of these taxa can accomodate a wide range of genetic relatedness. Human races aren't especially distinct as races/subspecies go, but the human species is not especially homogeneous, either.
quote: It's true that anthropologists tend to be hopelessly confused by the term, but fortunately the rest of us can get along with it just fine. John
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Mammuthus Member (Idle past 6495 days) Posts: 3085 From: Munich, Germany Joined: |
quote: If it can change based on your "original sense" then how can it give an accurate view of our species diversity? Again, this is my problem with the concept of race i.e. trying to fit precisely defined categories on a highly variable distribution.
quote: Sorry I did not make myself clear. L. cyclotis until recently was a sub-species and only after the O'Brien groups study did it get elevated to species. There is a similar study in the first issue of PLOS by Fernando et al. on Asian elephants demonstrating that E. maximus from Borneo are actually a subspecies that probably diverged around 300 kya. My point was, it was very difficult to demonstrate lack of gene flow and that enough divergence exists to even suggest that these populations are in fact different sub-species or species in the case of cyclotis. And you think one can then apply strict "racial" categories (whatever those would be) to H. sapiens were there is extensive gene flow? A comparative approach may also not serve to calibrate the differences among H. sapiens and other mammals because it is unclear if the evolutionary histories, mutation rates, etc. are equivalent among mammlian groups. I have used Comstock's microsat primers on mammoths by the way and one sees that they demonstrate far lower heterozygosity and numbers of alleles than E. maximus or L. africana for these loci (it's not published so you won't find it in Pubmed yet). One already sees extreme differences in numbers of alleles and heterozygosity among extant elephant species reflecting the differences in their evolution. Regarding Lake Victoria cichlids, the species designations are not uncontroversial though the original work of Schliewen and colleagues on sympatric speciation is fascinating...but nobody is calling them Lake Victoria cichlid races. That race, subspecies, and species can accomodate an extreme range of genetic diversity among groups suggests that the terminology is inadequate. If you give me a sample and tell me it is African or Asian...how would this guide my forensic work? would it be enough for a significant comparison to be made to other groups if I genotype it? Which genotype represents which race? What is a race? In this thread alone I have seen probably a dozen different definitions appear. Given the difficulty of biologically defining species, it seems to be a wasted effort to try to precisely categorize humans into the even more fuzzy concept or races.
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Too Tired Inactive Member |
Mammathus writes:
quote: I'm not familiar with the morphological differences that led to the former subspecies designations for forest and savannah elephants in Africa, but the lack of gene flow is readily apparent in the genetic data for people who have genetically characterized a lot of different species. I don't know where the difficulty is you're talking about. In my humble opinion Fernando et al. have overinterpreted a small amount of genetic data in trying to support their hypothesis that the Borneo elephants have Pleistocene origins. Maybe they're right, but there's nothing in their analysis of six loci that argues strongly against the 16th-18th century introduction hypothesis. It's up in the air whether the Borneo population should be considered a true subspecies even with those big pairwise Fst values. Look at the microsatellite heterozygosity - .014 compared to .7-.8 in humans. Fst is basically (Ht-Hs)/Ht so when Hs is practically nil like in these elephants, Fst is not very meaningful. Lack of gene flow with other populations is obvious though from the severe loss of alleles, most likely due to drift in a small isolated population. Whether it's been happening for 300 years or 10,000, who knows.
quote: What's a "strict racial category"? Sounds like an oxymoron. How much gene flow is "extensive"? You can't build a very solid case against human races using vague terms like these. You have to show us that gene flow has indeed been "extensive" compared to gene flow among groups within lots of other species. Stephen O'Brien has said publicly that people who don't believe in the biological reality of human races are basically ignorant of population genetics, although he said it more nicely.
quote: Of course evolutionary histories are not equivalent. But why shy away from a comparative approach? You were using one yourself when you wrote that it's preposterous to compare human group differences to those found among subspecies.
quote: Well, you can propose some new terminology if you like. I agree that it would be wasted effort to try to precisely categorize all humans into racial categories, but it works pretty well for several billion people and at least provides a frame of reference for the rest. Your new terminology will have to do at least that well. John
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sfs Member (Idle past 2553 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:Then you are not someone who should be writing a FAQ on human races. Write a FAQ on human diversity or on human subspecies, but if you're not interested in the issues involved in the use of the term "race", just leave the subject alone. quote:It's not that there's so much confusion about what race means to the man on the street, or to an anthropologist, or to the geneticist. It's that they each means something different. You, unfortunately, contribute to the confusion by writing as if the term carried only a single meaning. It doesn't. quote:No, but I know many, many people who consider a European-looking person black if he has any stereotypical African features, especially if he is known to have some African ancestry. All the people who considers Colin Powell an African-American (including himself), for example, or all the people who call Tiger Woods a "black athlete". I am also aware that someone else who has an identical amount of African ancestry but who was from Latin America would be quite unlikely to be considered black. That's how race actually works in the U.S.
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Mammuthus Member (Idle past 6495 days) Posts: 3085 From: Munich, Germany Joined: |
quote: I asked you what a "race" is....Peter in this thread has claimed there is a clear basis for "race" in the results of human population genetics studies and from the genome project. You seem to be advocating this same position yet neither of you has produced a definition of what a "race" or what the "racial" divisions we should be accepting are. As sfs pointed out, you are conflating several different meanings of "race" and assuming your concept is somehow the most common understanding of the term. If anyone is using vague terminology it is those who variably define "race" to suite any particular need. As for comments by O'Brien, everyone can have their opinion...science and scientific definitions should not be based on megalomaniac posturing. Leave that to the rock stars.
quote: Yes, I do advocate a comparative approach. But I do not advocate assuming a priori that the genetic diversity in one species can be used as a direct measure of the evolutionary history of another. Even if the genetics are similar, the evolutionary histories could have been very different. You are comfortable with the concept that cichlids can evolve by sympatric speciation and that even with low levels of genetic divergence among groups, that they can be considered species...I am fine with that. But what evidence is there that humans have evolved in this way? Would you advocate then that there is an African "race, sub-species, species" of H. sapiens? I know a morphologist who does though he was equally vague in his definition of "race" and "species"
quote: I'm not studying humans...Let O'Brien propose the terms if he thinks everyone besides himself is a rube. I am just not convinced that "race" is a useful concept as applied to defining human groups biologically. After participating in this thread, I now am skeptical that any two people share a common concept of what "race" is much less that it "works for billions of people". I note that plenty of scientists are perfectly happy allowing species definitions and concepts to proliferate "phylogenetic species concept, phylogeographic sub-species etc" yet somehow "race" is invariant and billions of people are all sharing exactly the same definition from scientists to laymen?
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Too Tired Inactive Member |
Mammuthus writes:
quote: My stance in this debate is that the racial division of humans is the default position, the status quo, and that the campaigners against human races have to convince us otherwise. So, slightly differently from how you've characterized Peter's take on genetics, I'd say that the evidence *against* human races is *not* found in genetic data. On the other hand, knowing as we do that human groups are interfertile and knowing what the population genetics of other subdivided species look like, I wouldn't argue much with Peter's assessment. As far as a definition of race, not only have I provided some quite in-depth discussions of the concept from various experts on my web site Just a moment... but I've provided an actual working definition of subspecies in my race faq which I can offer as a definition of race as well since I consider the terms to be synonymous. If I've overlooked a similar contribution by yourself in this thread, please point me to it. Which racial divisions to accept: well, for the major races Cavalli-Sforza preferred (prefers?) the Big Three, Wright would add Amerindians for four, five works well too, but I agree completely with Klein & Takahata that the number doesn't matter, you can be a lumper or a splitter as you wish.
quote: I agree that similar genetic make-up can be the result of very different evolutionary histories, but taxonomic terms aren't really intended to describe evolutionary histories - that would be a tall order. I'm not aware of any evidence or reason to think that extant humans have evolved by sympatric speciation. I would agree that sub-Saharan Africans comprise a major human race (and therefore, technically, a subspecies). I'm not aware of there being more than one species of H. sapiens.
quote: Like I said, it's always about definitions. The vast majority of people in the world who have had any amount of exposure to racial diversity probably have a very adequate sense of what race means. There's any number of concepts that we deal with all the time that aren't and can't be precisely defined - it makes no difference. All this agonizing over how race is defined just doesn't ring true, especially when it comes from those who haven't figured out how the term is used in non-human taxonomy. John
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