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After my online research on the subject, I learnt that, biologically speaking, many scientists believe that there is no such thing as a race, because Homo sapiens species is only 200,000 years old, which have not allowed for any significant genetic diversification yet, and our DNA is 99.99% similar. I've read statements that there can be more genetic variation inside a racial group than between different racial groups, meaning that, for example, two individuals from the same population can have less in common with each other than with an individual from another population.

Wikipedia quote:

Scientists consider biological essentialism obsolete, and generally discourage racial explanations for collective differentiation in both physical and behavioral traits


Q1: If Homo sapiens has no races (according to biologists), why are we so different morphologically? (hair/eyes/skin colour and even athletic performance seem to differ between human populations)

Q2: Is it common for other species too, when genetically close populations have very different morphological traits? Are there any other mammal or animal species that exhibit biological diversity comparable to human diversity, and how do taxonomists treat these species? (excluding intentionally bred domestic species to keep the comparison fair)


The question has been paraphrased to emphasize that it is the biological debate that is in question, not the sociopolitical. I.e., why is there no consensus in evidence and opinions of scientists?

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5 Answers 5

up vote 13 down vote accepted

Firstly, it's not true that you can't tell racial background from DNA. You most certainly can; it's quite possible to give fairly accurate phenotypic reconstruction of the features we choose as racial markers from DNA samples alone and also possible to identify real geographic ancestral populations from suitable markers.

The reason that human races aren't useful is that they're actually only looking at a couple of phenotypic markers and (a) these phenotypes don't map well to underlying genetics and (b) don't usefully model the underlying populations. The big thing that racial typing is based on is skin colour, but skin colour is controlled by only a small number of alleles. On the basis of skin colour you'd think the big division in human diversity is (and I simplify) between white Europeans and black Africans. However, there is vastly more genetic diversity within Africa than there is anywhere else. Two randomly chosen Africans will be, on average, more diverse from each other than two randomly chosen Europeans. What's more Europeans are no more genetically distinct overall from a randomly chosen African than two randomly chosen Africans are from each other.

This makes perfectly decent sense if you consider the deep roots of diversity within Africa (where humans originally evolved) to the more recent separation of Europeans from an African sub-population.

It's also worth noting that the phenotypic markers of race don't actually tell you much about underlying heredity; for example there's a famous photo of twin daughters one of whom is completely fair skinned, the other of whom is completely dark skinned; yet these two are sisters. This is, of course, an extreme example but it should tell you something about the usefulness of skin colour as a real genetic marker.

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Yahoo answers say you can't tell race from DNA... that's why I mentioned it. I also never heard this in crime investigations or detective stories... are you sure we can? Just double-checking, by no means I imply that my sources are credible. Regarding skin colour, we can also consider that the skin colour of a Caucasian can vary from pale-white to red to dark-brown at different levels of UV exposure. These changes are only in the phenotype, not in the genotype. What about athletic performance though? It's something more than just skin tinge. It must be related to organ systems, muscles, etc. –  Th334 Jan 11 at 13:46
    
It depends what you mean by race; because race isn't actually meaningful you obviously can't reconstruct it. However, given a DNA sample it is possible to make a good approximation of the appearance of the person the sample is from. I don't think such a reconstruction would be reliable enough for law enforcement purposes, but it's pretty good none-the-less. –  Jack Aidley Jan 11 at 16:52
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@Herman Suppose that in some sport it is an advantage to be very tall. Then because all genetic variation of humans is in Africa, you would expect the tallest people of the world to be in Africa. But you would also expect the smallest people in the world to be an African people. Similarly, in Africa you would find those who can sprint fastest. But you would also find in Africa those which are the slowest runners. So expect all variation to be on that continent. Also remember that those Africans who were deported to the Americas as slaves, all came from a small area on the west coast of Africa. –  Jeppe Stig Nielsen Jan 11 at 20:24
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@Herman: Evolution follows a branching, hierarchical structure (broadly, it's more complicated than that) and Europeans group within the various African populations, i.e., they're essentially a subpopulation of a particular African population. –  Jack Aidley Jan 13 at 8:22
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@Herman: No, although that can also be a factor. Have a look at this image - bit.ly/1iHOMss - and note how there is no clade that includes both Africans but not the Europeans. This is because the European population is a subpopulation of the African population. The two African populations shown are as different from each other as the European population can be from the first African population. In reality, there are many more distinct African populations than shown here. –  Jack Aidley Jan 13 at 15:43

Well, that's just it, we don't actually have much phenotypic variation. For example, compare this:

enter image description here

to this:

enter image description here

or this:

enter image description here


Or this:

enter image description here

to this:

enter image description here


This is phenotypic variation:

enter image description here


And of course, you can't beat the birds of paradise when it comes to variation (though, strictly speaking, these are different species):

enter image description here


So, as I hope is clear from the images above, phenotypic variation among humans is tiny compared to other species. We just notice small differences much more because, well, it's us so little differences are much more noticeable.

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This ridiculously obvious illustration somehow put the issue in a totally different perspective for me. Quite an eye-opener. I think this is a brilliant answer, thank you for the effort. –  Th334 Jan 11 at 12:12
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Hmm... I'm not sure how useful comparing natural variation (human phenotypes) to artificial variation (dogs, cats and pigs) really is. Are you humans really less phenotypically variable than wild animal species? I guess ring species might make a good comparison? –  Jack Aidley Jan 11 at 12:52
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@terdon: The bird of paradise are not a species, as you note in your answer and I don't think it's clear - at all - that humans show relatively little phenotypic variation. I would say that humans are probably on the high side (likely due to the huge range that humans occupy). –  Jack Aidley Jan 11 at 13:03
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@Rodrigo yes, that was added after I posted this answer. –  terdon Jan 14 at 19:57
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@Herman don't. You should edit your question in response to the answers you get. Your Q should always reflect what you are actually asking. I will look into this in more detail and update as soon as I get the chance. –  terdon Jan 15 at 1:44

It could not fit in a comment…

1) When you say "phenotype" you mostly mean skin color, size of the nose, hair, shape of the eyes, height,… All these traits that we manage to find to explain population structure among humans. But you forget all the rest of the phenotypic diversity. We you choose 1000 randomly chosen traits (external morphology and other stuff) and make a PCA. Will the main axes explain much of the inter-subpopulation (or inter-racial) diversity? I am not sure about that. One cannot use one subset of the total phenotypic or genetic variance and use it in order to define several species within what was previously thought to be one. It is not because two genes are associated with the same population structure that one can define two different species.

2) You say: " [..] is it reasonable to use a genetic approach to races and claim that biological races do not exist, while it seems to be a poor indicator, when it comes to comparison of phenotypes of human populations". Similarly, one could say "Bats look like birds. We consider them as being mammals just because that is what scientific observations (genetic data or in-depth observation of the phenotypic variance) says. But should we follow scientific explanations when our intuition tell us that these observations are poor indicators?

I have to confess though that I don't know much about phenotypic or morphological variance among humans. And I'd be curious if someone could give some words about that and whether or not much of the phenotypic and morphological variance is explained by what we consider being racial groups. It might be possible that very little of the total phenotypic variance is explained by racial groups but quite a lot of the face morphological variance is explained by racial groups.

As a sidenote: For species that can reproduce exclusively with sex, we tend to use the concept of reproduction isolation to define species and I really don't think (although I might be wrong) that there is a pair of racial groups are sexually incompatible (however you delimit the racial groups)

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I would be very, very surprised to find out that any two racial groups cannot reproduce: not only we are one species, we are also one subspecies, and we share over 99.9% of the same genome. The world would be a totally different place if this was true, from the sociopolitical perspective. It might happen one day though. I hope collectively we'll be much wiser when and if it does happen. –  Th334 Jan 11 at 12:49
    
Yes, that would be immensely surprising indeed! But I don't think any study ever reviewed cases of reproduction between all "considered social groups". –  Remi.b Jan 11 at 12:59
    
On the other hand, it also means that no one has ever noticed any suspicious trends in child mortalities from cross-racial parents to think about such a survey. I also believe that gentlemen from the Third Reich would be very interested in this question, and they conceivably could do some research, which wasn't published because the results were negative. It's just my guess though, and I'm no specialist in history. –  Th334 Jan 11 at 13:08
    
Remi, sorry, I'm not familiar with PCA, and the Wikipedia page is intimidating. Was your first point that we share so much traits in common that the ones that distinguish us from each other are statistically non-significant? –  Th334 Jan 11 at 14:04

I decided to summarize a competing hypothesis to make our answers more balanced. I also tried to address the question about the degree of human morphological diversity compared to other animals.


According to Woodley (2010), it is plausible that H. sapiens does not belong to one species and subspecies (i.e. is polytypic). Some of the data he uses to support this hypothesis could be useful for answering our question. He claims that H. sapiens, which is often considered monotypic, posses higher levels of morphological diversity, genetic heterozygosity and differentiation than many animal species which are considered polytypic.

Woodley cites a study by Sarich and Miele, who claimed that morphological differences between humans, on average, are equal to the differences among species within other mammalian genera (excluding species bred for domestic purposes), and are typically more strongly marked than in other animals.

However, morphological differences are known to be caused by little genetic differences too, like in the case of domestic dogs, which are still considered to be one species. Therefore, Woodley presented further evidence that looked on these inconsistencies in classification using allele frequencies and genetic diversity.

He presented data from a wide range of studies, which compares genetic diversity of various mammalian species based on heterozygosity (H), which is a common indicator for genetic diversity, and describes whether both alleles are the same or not on a studied locus. According to this data (which you can find in the linked paper):

  • Chimpanzees exhibited H of 0.63-0.73, which is very similar to H found in humans (0.588 - 0.807), however, chimpanzees are divided into four subspecies.
  • Some species like the grey wolf even exhibited a lower H (corresponding to lower genetic diversity) than humans (0.528 vs 0.588 - 0.807), while the grey wolf has been divided into as many as 37 subspecies.

This data suggests that humans are more diverse both morphologically and genetically than some of the other mammalian species that have been divided into subspecies.

References:
Woodley, M. A. (2010). Is Homo sapiens polytypic? Human taxonomic diversity and its implications, Medical Hypotheses, 74, 195-201. doi:10.1016/j.mehy.2009.07.046 (full-text PDF)

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It's a political question. They think (or pretend?) they're fighting racism denying human races. At the same time, a country with more species and subspecies receive more funds for conservational programs (see my answer). –  Rodrigo Jan 14 at 19:32

It seems to me that many answers to this question suffer from the nasty habit of "political correctness". As a zoologist, I never heard of somebody sequencing the whole DNA of any species to decide when to use or not the term "race". If a group of animals comes from a side of a river, and the other comes from the other side, and they have one or a few distinctive features (color of chest pelage, tuffs of hair in the sides of head, etc), that's enough to call them both different races (or even subspecies). Of course some geographical isolation has taken place, although it hasn't been long enough to divide the two (or more) populations into full species. The same logic should be used to humans, right? Maybe some folks believe that, pretending there are no human races, then the question of racism is "solved"? Bad logic, to me.

Look at http://www.worldbirdnames.org: they cite 10,518 extant species of birds and 20,976 subspecies. About 2 subspecies per species. How do they do that? (No DNA for most of them.) Subspecies/races are usually from different regions (like human races), their vocalizations are usually different (like human races) and their colors sometimes vary (not as much as in human races). My point is: there is NO SCIENTIFIC REASON to say there are no human races, if we're using zoological reasoning. (Unless we are not animals anymore!)

For mammals, http://www.catalogueoflife.org/col/browse/classification/kingdom/Animalia/phylum/Chordata/class/Mammalia/match/1 cite: 4,843 species, 2,998 infraspecific taxa. Again, if someone show me they did complex DNA analysis for most of those infraspecific taxa, and those analysis showed that variation inside races is smaller than between races, THEN I will be forced to agree with them.

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Maybe, but the "why?" question is beyond our scope here, I asked the "is it?" question, which is purely biological. If you improved your answer by expanding on your experience as a zoologist when it comes to defining subspecies and removed the "why?" question of your own -- I, personally, would like your answer much more :-) –  Th334 Jan 15 at 0:07
    
I just inverted your question: "If human populations have several distinct phenotypes, why (they say) there are no human races?" Or, from other point of view, I questioned your first "If" in the title. It's not just a biological question, to me it seems much more a political one. How many biological races have been described? Or subspecies? Take a look at IUCN Redlist, for instance, or Zoological Records in many universities. Do you really think they scanned their DNA in depth? There's no biological reason for a different approach on human beings. As I said, it's just politics. –  Rodrigo Jan 15 at 0:51
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I think you make a fair point... I might paraphrase my question. Why paraphrasing? Although intuitively I agree with you that it might have something to do with politics, it's not really something that I wanted to discuss, and it's probably not even allowed to be discussed on Biology SE. If we do, someone will ask: "Well, how do you know that it's all just politics", and here we go, it becomes a debate with no science behind it, just opinions. –  Th334 Jan 15 at 1:00
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Good argument, Rodrigo, I don't see how I could contradict right now. One thing though, just because SE is a little like Wikipedia in terms that we try to save good and detailed answers for future reference by other users, if you could edit your answer to express this idea, you would definitely get a +1 from me, and potentially an "accepted answer" too. –  Th334 Jan 15 at 1:37
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Rodrigo, ok, most of subspecies and "races" in zoology don't have DNA analyzed but are still considered to be separate. However, in the case of humans it is analyzed, so it would make sense to apply this information if it indicates that humans cannot be grouped in races, wouldn't it? (whether that's what our DNA indicates or not is another, not mentioned by you, question) –  Th334 Jan 15 at 2:41

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