We aren’t all the same- science is finding evidence of genetic diversity between populations as well as between individuals

Let’s celebrate human genetic diversity

Bruce Lahn and Lanny Ebenstein Nature, 8 October 2009

Science is finding evidence of genetic diversity among groups of people as well as among individuals. This discovery should be embraced, not feared, say Bruce T. Lahn and Lanny Ebenstein.

A growing body of data is revealing the nature of human genetic diversity at increasingly finer resolution. It is now recognized that despite the high degree of genetic similarities that bind humanity together as a species, considerable diversity exists at both individual and group levels (see box, page 728). The biological significance of these variations remains to be explored fully. But enough evidence has come to the fore to warrant the question: what if scientific data ultimately demonstrate that genetically based biological variation exists at non-trivial levels not only among individuals but also among groups? In our view, the scientific community and society at large are ill-prepared for such a possibility. We need a moral response to this question that is robust irrespective of what research uncovers about human diversity. Here, we argue for the moral position that genetic diversity, from within or among groups, should be embraced and celebrated as one of humanity’s chief assets.

The current moral position is a sort of ‘biological egalitarianism’. This dominant position emerged in recent decades largely to correct grave historical injustices, including genocide, that were committed with the support of pseudoscientific understandings of group diversity. The racial-hygiene theory promoted by German geneticists Fritz Lenz, Eugene Fischer and others during the Nazi era is one notorious example of such pseudoscience. Biological egalitarianism is the view that no or almost no meaningful genetically based biological differences exist among human groups, with the exception of a few superficial traits such as skin colour. Proponents of this view seem to hope that, by promoting biological sameness, discrimination against groups or individuals will become groundless.

We believe that this position, although well intentioned, is illogical and even dangerous, as it implies that if significant group diversity were established, discrimination might thereby be justified. We reject this position. Equality of opportunity and respect for human dignity should be humankind’s common aspirations, notwithstanding human differences no matter how big or small. We also think that biological egalitarianism may not remain viable in light of the growing body of empirical data.

Many people may acknowledge the possibility of genetic diversity at the group level, but see it as a threat to social cohesion. Some scholars have even called for a halt to research into the topic or sensitive aspects of it, because of potential misuse of the information. Others will ask: if information on group diversity can be misused, why not just focus on individual differences and ignore any group variation? We strongly affirm that society must guard vigilantly against any misuse of genetic information, but we also believe that the best defence is to take a positive attitude towards diversity, including that at the group level. We argue for our position from two perspectives: first, that the understanding of group diversity can benefit research and medicine, and second, that human genetic diversity as a whole, including group diversity, greatly enriches our species. 

Emerging understanding of human genetic diversity

Genetic diversity is the differences in DNA sequence among members of a species. It is present in all species owing to the interplay of mutation, genetic drift, selection and population structure. When a species is reproductively isolated into multiple groups by geography or other means, the groups differentiate over time in their average genetic make-up.

Anatomically modern humans first appeared in eastern Africa about 200,000 years ago. Some members migrated out of Africa by 50,000 years ago to populate Asia, Australia, Europe and eventually the Americas. During this period, geographic barriers separated humanity into several major groups, largely along continental lines, which greatly reduced gene flow among them. Geographic and cultural barriers also existed within major groups, although to lesser degrees.

This history of human demography, along with selection, has resulted in complex patterns of genetic diversity. The basic unit of this diversity is polymorphisms — specific sites in the genome that exist in multiple variant forms (or alleles). Many polymorphisms involve just one or a few nucleotides, but some may involve large segments of genetic material. The presence of polymorphisms leads to genetic diversity at the individual level such that no two people’s DNA is the same, except identical twins. The alleles of some polymorphisms are also found in significantly different frequencies among geographic groups. An extreme example is the pigmentation gene SLC24A5. An allele of SLC24A5 that contributes to light pigmentation is present in almost all Europeans but is nearly absent in east Asians and Africans.

Given these geographically differentiated polymorphisms, it is possible to group humans on the basis of their genetic make-up. Such grouping largely confirms historical separation of global populations by geography. Indeed, a person’s major geographic group identity can be assigned with near certaintly on the basis of his or her DNA alone (now an accepted practice in forensics). There is growing evidence that some of the geographically differentiated polymorphisms are functional, meaning that they can lead to different biological outcomes (just how many is the subject of ongoing research). These polymorphisms can affect traits such as pigmentation, dietary adaptation and pathogen resistance (where evidence is rather convincing), and metabolism, physical development and brain biology (where evidence is more preliminary).

For most biological traits, genetically based differentiation among groups is probably negligible compared with the variation within the group. For other traits, such as pigmentation and lactose intolerance, differences among groups are so substantial that the trait displays an inter-group difference that is non-trivial compared with the variance within groups, and the extreme end of a trait may be significantly over-represented in a group.

Several studies have shown that many genes in the human genome may have undergone recent episodes of positive selection — that is, selection for advantageous biological traits. This is contrary to the position advocated by some scholars that humans effectively stopped evolving 50,000–40,000 years ago. In general, positive selection can increase the prevalence of functional polymorphisms and create geographic differentiation of allele frequencies. 

A news worthy article, that won’t probably get the attention it deserves in the general media. I’ve noticed over the past few years more and more papers are being published along these lines, and I’d just like to applaud them for having the courage to put this in print, as this kind of published work (observing what are essentially racial differences) can really endanger your career. Most notable was this …

It is now recognized that despite the high degree of genetic similarities that bind humanity together as a species, considerable diversity exists at both individual and group levels

Which really goes counter to what it generally presented to the public in those cosy channel four and BBC documentaries like ‘In the blood’  and ‘ Race, the last taboo’. Prof. Jones will not be a happy man when he reads this. Also worthy of attention was this (condensed, it’s in the text as a whole) …

Biological egalitarianism is the view that no or almost no meaningful genetically based biological differences exist among human groups …..We believe that this position, although well intentioned, is illogical and even dangerous…We also think that biological egalitarianism may not remain viable in light of the growing body of empirical data.

So there you go. We aren’t all the same. I’ve believed for the past seven years, ever since I started to show a deeper interest in anthropology and genetics, the ‘no such thing as race’ paradigm was driven by (well meant) egalitarianism ideology and not fact. If there’s no such thing as race, there can’t be racial differences and, ergo, no racism. I think that Lahn’s and Ebenstein’s hopes for a grown up acceptance of between-group differences may be unfulfilled, as the average human just isn’t that reasonable.

16 responses to “We aren’t all the same- science is finding evidence of genetic diversity between populations as well as between individuals

  1. Biological egalitarianism is the view that (…) no meaningful genetically based biological differences exist among human groups

    And this is the fact. There are differences in, say, pigmentation? Sure; we did not need genetics to know that. But there are quite few credible biological adaptations with such geographical differences.

    For example, a quite interesting read in this issue of pigmentation genetics is Coop 2009. One of the things that most called my attention was that all the regional alleles are present in Africa south of the Sahara (fig 4). That means that: (1) they existed probably before the OoA and were amplified by founder effect plus adaptative pressure, and (2) that there are many other genes and epigenetic factors affecting these matters (because Africans with the “whiteness allele” are still black).

    Another important factor is that mostly single genes are not determinant, but the accumulation of various, often many of them, plus environmental factors (and here I mean biological factors like epigenetics too).

    So why that insistence with genetic predestination when all is so fuzzy and plastic? Most of the adaptative (or drifted) genes that have been found, if not all, correspond to things we already knew without looking at the genes: pigmentation, cartilage structure or known health issues.

    We are looking at the script of a program we are way too familiar with. The code is different but says that program works more or less as we thought it did. Just common sense.

    “Whoa, I have discovered the gene of whiteness!” (90% media hype anyhow).

    So? What do you want, the Nobel prize? It’s nice to know but in a sense I already knew that pigmentation was essentially hereditary.

    • Hi9 Luis.

      I’m always bemused at the isistence we are all ‘essentially the same’ and an isistence that hereditary plays little part in who we are.

  2. Well, I’m always bemused at the cliché insistence on genetics being an all-encompassing totalitarian program. Genes count but they are normally not that different and, importantly, they are much more plastic than some want to believe.

    There’s a silent fight of paradigms within the genetic research field: on one side are the old-fashioned who claim “genes predict all” and on the other hand the realists who see that single genes predict nearly nothing and that epigenetics (post-conception plasticity) is much in charge, activating or deactivating or just modifying the expression of genetic complex “programs” altogether.

    Genes alone explain only so much. And anyhow, as discussed above, there are not so many genes distributed along racial or geographical lines and, even those that are, show high intra-population variability. This is particularly true for Africa, where the diversity is so huge and where there were not the founder effects and relative isolation that happened in Eurasia.

    When you simplify the overall averaged effect, racial clusters do appear, of course. But when you look at the genes one by one and at individual level, you see that it’s just an statistical effect, not anything too real. And not anything that was not known before the advent of modern genetics in most cases.

    • see that it’s just an statistical effect, not anything too real

      Not really, it does have manifest biological differences Luis, and it’s possible to split into seperate species with less genotypic diversity than humans have as a group- cichlid fishes for example.

  3. “Genetic diversity is … present in all species owing to the interplay of mutation, genetic drift, selection and population structure”.

    Doesn’t that just sum it up completely? Yet so many of us are so convinced that humans are so completely different to all other species that we don’t vary across our geographic range.

    “There are differences in, say, pigmentation? Sure; we did not need genetics to know that”.

    Are you implying that that difference is not a result of genes? And skin pigmentation is not the only character that varies geographically.

  4. I agree, except that it’s worth noting that what we label as races is clearly not based on any kind of genetic evidence. For example there is greater genetic diversity between some groups of different black Africans than there is between some of those groups and Scandinavians. We really base our “race” labels on superficial features that don’t really give us a particularly good indicator of genetic variation (in many cases).

    • For example there is greater genetic diversity between some groups of different black Africans than there is between some of those groups and Scandinavians

      I agree, I’ve got a relative of Cape African ancestry and she gets lumped in with Bantu people under the current ‘folk’ races.

      Europeans- it’s hardly worth while differentiating us, we are so similar.

  5. It is not contradictory to say that we are all the same, or correctly nearly the same, and yet distinguishable and separable into types.

    Our sameness is from our genes which govern our essential body functioning, our skeletal structure, human as distinct from Gorilla or Chimpanzee, our tolerances to environmental changes and so on. Our differences is in how our genes function, mostly due to alleles, and ancillary genes which modify other genes.

    So the two statements are not incompatible. On the basis of massive numbers SNPs geographically separated ethnic groups and nationalities can be separated into their correct GPS homelands. Indeed, children can be placed closer to one parent or the other, or closer to siblings than others on the basis of SNPs. I know myself being one of eight children, how I thanked my lucky stars that I was different from the others, and my parents.

  6. Pingback: We aren’t all the same- science is finding evidence of genetic diversity between populations as well as between individuals « Ethos, Interrupted

  7. I stumbled across your blog the other day, it is great. My blog is similar except I throw in a lot of other topics that interest me besides anthropology (like philosophy and book reviews). I like how you stated that this is a research scrapbook in a way, that is a good way to describe my blog. Anyway, I reposted this post on my blog.

  8. “human as distinct from Gorilla or Chimpanzee”

    And they vary geographically as well. The different-looking populations are often refered to as (wait for it), Races.

    Anthropology.net has just posted an interesting article about Chinese H. erectus. Seems that H. erectus didn’t vary regionally, which I find extremely surprising. It means either there was very rapid migration from Africa (more rapid than that of modern humans, because modern humans have diversified into geographical races) or there was a surprising level of gene flow, amazingly so for a human species so ancient.

  9. “For example there is greater genetic diversity between some groups of different black Africans than there is between some of those groups and Scandinavians”.

    The obvious conclusion is that Africa contains several races. Even the briefest examination reveals this to be so. For a start we have Berbers along the Mediterranean side of the Sahara. And Pygmies in the densely forested Central West African Basin. Any apparent homgeneity of Africans is presumably the product of the relatively recent Bantu-speaking people’s expansion from West Africa. They seem to have mixed with pre-existing inhabitants along the way. Khoi-San at the Southern end are very different from most other Africans. Some claim similarity between them and some Ethiopians although these last may be partly a product of incoming Eurasian genes.

    So, we’re left with five races in Africa, distributed around the geographic margins: The Mediterranean Coast, the Central West African jungle and the Western, eastern and Southern points, with a mixture in the middle. Not so different from the situation we find in Eurasia.

  10. Two thoughts on “no such thing as race” that drive that debate.

    1. Line drawing: No U.S. census has drawn the boundaries in quite the same way, and different countries classify the same individuals differently (as you note in the Cape African case). For example, the Chinese distinguish between South Chinese, North Chinese and Koreans on sight, Americans don’t. Americans used to distinguish Northern Europeans from Southern Europeans as races or quasi-races, now both are considered “white.” There are different levels of branching and they are complicated by admixture at different rates. While the genetic diversity of populations is well established, the places it makes sense to draw lines that describe clusters is more art than science. The way lines are drawn has social reality that is reinforcing. Admixture of populations is more likely when the populations don’t perceive themselves as racially different. An Italian is much less likely to see ethnicity as a barrier to marrying a Swede now than would have been the case in 1909.

    A big part of the opposition to “race” is not to the notion that there are genetic differences between populations, but to the notion that the places one can draw the lines around clusters and branches is scientificallly definitive.

    Halotype studies, that show each population having a mix of halotypes found over a range much broader than the origin area or high frequency area of that haloptype illustrate the difficulty of abstracting from populations down to individuals when talking about genetic diversity.

    2. Culture as an element of “folk race”:

    Customary use of the term race includes a combination of clusters of physical characteristics (with some clusters rarely encountered in a society registering as ambiguous), with a usually associated membership in an ethnic culture. Even at a shallow level “folk race” is really appearance cluster plus dialect cluster, simplified into culturally created boxes.

    Hispanic, for instance, is a United States “folk race” even though it includes people of Iberian descent, Mestizos (Iberian-Native Americans), people with partial African descent, and others. A mixed race person of partially European and partially East Asian descent who grew up speaking English can appear quite a bit like a Mestizo, and has a fair amount of genetic similarity, but would rarely be considered one socially after saying even a few words.

    A Chinese adoptee raised in Alabama from shortly after birth is quickly disagregated from Chinese-American stereotypes, even though adoptee is pure Chinese genetically. Likewise an African immigrant is treated socially differently than an African-American, even though they may be descended from the same village in Africa have have quite similar genes. At first glance, an encounter with an anomolous individual can provoke confusion (the “what are you” response), but soon a new social category emerges.

    Aversion to “race” as a classifier use flows from stereotypes and predjudices based on these mixed clusters that acquire social meaning. Indeed “race” as the term is commonly used in American English really isn’t established until it is associated with an ethnicity and given social meaning that has real world effects.

  11. Hi Matilda – I’ve had this site marked in my Favourites for months & finally had a quick look. It’s excellent although some of the more technical genetic stuff is a bit over my head.

    I campaign on energy & environmental issues & am always wondering ‘where did it all go wrong?’. As a species we are amazing but look at the net result – poverty, pollution etc. Why were those who lived in balance with nature referred to as ‘uncivilised’ and wiped out by us Europeans? Although I have no academic training in anthropology, I am, like you, one of those who is convinced that there were several species of ‘Homo whatever’ living tens of thousands of years ago and those who prevailed tended to be the brutal, greedy ones. Makes sense – survival of the fittest & all that.

    The switch to settled agriculture was the beginning of our over-manipulation of the environment – it enabled sections of the population to specialise in work which was not linked to feeding ourselves and it enabled a few to own way more than the rest. Daniel Quinn wrote a fascinating book called Ishmael – basically there are ‘takers’ and ‘leavers’ – the latter lived in harmony with nature & he suggests that it was they who wrote (at least some of) the biblical texts as a warning that things were getting out of control. It seems, to me, that all religions have at their base a message of cooperation and caring for each other & the planet. Sadly, most religions have lost the plot a bit on that. By the way, I’m an athesist, not that it should matter.

    Skipping forward to now, we have developed a complex, globalised society thanks to the energy of fossil fuels. Now that the energy returns from fosil fuels are falling alarmingly (not to mention the depletion of ecosystems, fertile soils, fresh water & countless essential minerals) we are left with the seemingly impossible task of running the show with a lot less energy. Such talk is as popular as your race stuff but none the less important for being unpopular!

    I’m not sure how our low energy future is going to pan out but I do know that we need to move away from so many of the cherished (& probably wrong) views that humans are the pinnacle of evolution and that we can do anything if we put our minds to it. Yes, we’re smart when swimming in energy but I wonder how smart we’ll be without it. We’ve lost so many skills. Anyone who thinks evolution stopped with modern man simply does not understand evolution, genetics, ecology & the like.

    OK, rant over. Thanks again for your blog – I’ll keep an eye on it!

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