All One Species ?

There is a new paper about a recently discovered skull from Dmanisi, Georgia, an early Homo erectus.  Compared with a set of other erectus skulls from the same area and from about the same time, it looks as if this population had a fair amount of variation – so some are arguing that various skulls in Africa that were assigned to several different species may well all be members of a single fairly variable species.  Possibly evidence for lumpers, in their eternal struggle with splitters.

Milford Wolpoff, in reaction to this work, said “Everyone knows today you could find your mate from a different continent and it is normal for people to marry outside their local group, outside their religion, outside their culture,” Wolpoff told Agence France Presse. “What this really helps show is that this has been the human pattern for most of our history, at least outside of Africa,” he added. “We don’t have races. We don’t have different subspecies. But it is normal for humans to vary, and they have varied in the past.”

That’s all wrong. For most of human existence mating with people from substantially different groups was rare – usually very rare.  For one thing, there were no letters for your baby to send, let alone aeroplanes to take. Long-distance travel was very rare. Most people never even met anyone from another race or subspecies.

 If two populations exchange exchange genes much, they can’t become very different via drift. To be exact, you don’t expect to see much divergence in neutral gene frequencies as long as at least one individual is exchanged per generation.  You heard me right: ONE.  Assume that Old Stone Age people in sub-Saharan Africa were effectively a single population, while Neanderthals were another. Judging from the measured genetic distance between those two groups,  gene flow was very low –  averaging quite a bit less than one individual per generation for hundreds of thousands of years.

In terms of populations that exist today, Bushmen seem to have been isolated – really isolated, less than 1 mating across the line per generation – for something like 150,000 years. Until fairly recently.  In the Holocene, the last 10,000 years or so, there’s been a whole lot of shaking going on. Many Bushmen groups have a fair amount of Bantu admixture, and  surprisingly, they also seem to have a few percent of ancestry picked up from an expansion of pastoral peoples that (in part) traces all the way to the Middle East [Joe Pickrell’s work]. But that’s all recent.

Populations can also come to differ significantly because of natural selection, rather than drift. That can happen much more rapidly.  Gene flow between populations interferes with this process, but it takes a lot more gene flow to stop selection than it does to stop drift.

None of this means that individuals from long-isolated populations couldn’t mate successfully, given the chance.  It takes a long time for that kind of infertility to develop –  more than a million years, on average. Lions and tigers, which have been separated for about two million years,  can still produce fertile female offspring, although male ligers. are sterile.  This makes another point: fertility isn’t all or nothing. There can be degrees of interfertility.  A given kind of hybrid mating might have an average fertility that was 90%, or 50%, or 10% of normal. Haldane’s rule says that, in mammals, male hybrids are more likely to take it in the shorts.  Or, as genetic distance between parents increases, fertility problems show up first in male offspring.

If you knew how long ago Neanderthals and Denisovans split off from the ancestors of anatomically modern humans (something like half a million years), it was possible to see that AMH could probably mate successfully with those archaic humans. In the course of expanding out of Africa, AMH had to run into Neanderthals, and so some degree of admixture was likely.  And since even a wee bit of admixture is enough to transmit alleles with a selective advantage,  that admixture had some functional consequences [upcoming paper by Sankararaman].  None of this means that Neanderthals weren’t significantly different from modern humans.

It doesn’t mean that subspecies didn’t exist, or don’t exist.   And the existence of some interfertility doesn’t mean that there were no fertility problems in AMH-Neanderthal crosses.   The amount of Neanderthal ancestry is considerably lower than average on the X-chromosome [about a third of the normal fraction] .  This suggest a certain amount of hybrid incompatibility, since incompatibility loci are known to concentrate on chromosome X [recent work from Sriram Sankararaman at the Reich lab] .

The odds are fair that a modern human could successfully mate with a Floresian hobbit, assuming that it’s really an island-dwarfed version of Homo erectus.   Even though it was three feet tall and had a chimp-sized brain.  Somehow that doesn’t convince me that races and subspecies don’t exist.  Nor does it convince me that mating with people from very different populations was common.  Mating across the lines happened before the Holocene, and sometimes, when it transmitted adaptive alleles,  it was very significant.

But it was rare.

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This entry was posted in Archaic humans, Denisovans, homo erectus, Neanderthals, Uncategorized. Bookmark the permalink.

40 Responses to All One Species ?

  1. Paul Conroy says:

    Here’s aquote from an article about Dmanisi – Skull 5:

    “The broad face, large teeth, and snout-like skull… What intrigued them about the last skull, called Skull 5, were very primitive characteristics of prehuman ancestors, combined with distinct hallmarks of Homo erectus, an early human that emerged about 2 million years ago whose remains have been found in Europe and Asia. The face, Rightmire said, is strikingly large, with a wide nose and flaring, thickened cheek bones. Its mouth protrudes, almost like a muzzle, quite unlike modern humans. Its brain is also small—about a third of the size of a modern human brain—but the skull and the shape of the back of the skull resemble that of Homo erectus”

    Does this sound like a more extreme Hybrid to you? Rather than AMH+Neanderthal, or AMH+Hobbit, how about Homo Erectus+Sus Scrofa or Pan Troglodydytes+Sus Scrofa ???

    http://www.macroevolution.net/human-origins.html

    It would explain how Pig kidneys and other organs work just fine in humans, and a whole bunch of other strange coincidences…

  2. Anonymous says:

    “It doesn’t mean that subspecies didn’t exist, or don’t exist.” The problem is that drawing “subspecies” lines is even more problematic than drawing “species” lines. Of course there are genetically distinct populations, but how do you decide weather they are “races” or “subspecies” or anything? And the old, pre-molecular, quasi-folk rule to the effect that “if you can tell ’em apart more often than not, call ’em a subspecies” isn’t very helpful-tellapartability doesn’t necessarily coincide very well with genetic distance, plus it is relative (one can tell apart Japanese from Koreans-so are they different races?). To objectively decide weather you have races, subspecies, or anything, you need an objective and biologically meaningful way of drawing such lines-otherwise the “race doesn’t exist” idea is as wrong as any other.

    • reiner Tor says:

      I actually think along the lines of Sarich and Miele, who wrote that the tellapartism works quite well with animals (even if genetic studies usually finetune the picture), and that, well, if you can tell Swedes apart from Greeks, then yes, Mother Nature gave us that many races. I mean, I actually think Greeks do look different from Greeks, they do behave different, they stem from distinct populations which had very little to no contact for millennia – so they are different races.

      Of course they probably resemble each other more than either of them resembles say Chinese or the Xhosa, so maybe we need to find an in-between category. You might for example want to call Greeks and Swedes clines of the same race (white Europeans), whereas the Xhosa might be said to be members of an altogether different race. There might be categories where the difference is larger than in the Greek/Swedish case (Egyptians might be more different from either than they are from each other), yet where this difference is still smaller than in the case of the Greek/Xhosa or Swedish/Xhosa pair.

      Mother Nature unfortunately never restricts itself to a few easy to recognize, comfortable and fairly distinct categories, sometimes the number of categories is very large, their hierarchies are messy, etc. The reason for that is that categories like race or species are creations of the human mind to help us better approximate reality. Race as such does not exist in a very clear-cut way, but their non-existence is not clear-cut either. The question is, are they real enough to be considered a reality? (The answer is a big yes.) But they are fuzzy, often with not very well-defined borders (especially in the case of recently or a few millennia ago hybridized populations).

    • gcochran9 says:

      Define a criterion that’s useful for the problem you’re looking at and then use it.

      • Anonymous says:

        That was my point. Using “race” as equivalent to “a distinct population” (so that one can correctly speak of “the Asian race” as well as of “the Korean race”) is fine, but when arguing if distinct populations are “races”, one needs other criteria of raciality. Otherwise people arguing the existence-or-not of race can go on forever without even meaning anything.

    • Chuck says:

      “To objectively decide whether you have races, subspecies, or anything, you need an objective and biologically meaningful way of drawing such lines-otherwise….”

      *face palm* You can simply define races as sub-specific genetic populations (as done in biology). Genetic cluster analysis, then, would be your objective way.

      Kitcher (2007): “So there is a genuine issue about level or fineness of grain, one that can only be settled on pragmatic grounds: the clusters, or races, will be picked out by fixing the number so that the resulting division best accords with the inquiries we find valuable. Picking out new clusters preserves, in an important sense, the boundaries that have already been drawn. You may find new subdivisions within a previously identified unit, but you do not generate new clusters that straddle earlier ones. If two populations are assigned to different clusters at one value of the parameter, they remain separated at all higher values. On this basis, one might conclude that the pragmatic component in dividing the species is relatively insignificant,just a matter of finding the appropriate level in an objective tree-structure.”

  3. Anonymous says:

    “Either we must debunk downward by showing that science gives the best description of what is real, with the rest counting as nothing more than epidermal illusion; or, we must debunk upward by showing that everything is constructed by language, society, perception, or events, so that only naïve, life-hating oppressors would insist on a “reality” hiding beneath the play of surfaces”

  4. P says:

    If two populations exchange exchange genes much, they can’t become very different via drift. To be exact, you don’t expect to see much divergence in neutral gene frequencies as long as at least one individual is exchanged per generation. You heard me right: ONE.

    Lou Jost has argued that this is not true, and that the misconception results from the use of faulty indices of population differentiation. I quote from a blog comment of his:

    In the comments under Jerry’s blog, John Harshmann raised a related issue. He claimed that since one migrant per generation was enough to prevent divergence of populations due to drift, human races should not show much divergence (since migration between most groups surely exceeds one individual per generation). This argument is part of the same population genetics lore as the statements about variation. It is based on the misinterpretation of Gst or Fst as actual measures of genetic divergence between groups. Gst is the between-group heterozygosity divided by total heterozygosity. In my example above, with two completely distinct groups that share no genes at all, Gst is very low, about 0.05, which would usually be interpreted to indicate little differentiation between groups (clearly a false conclusion). The idea that one migrant per generation is enough to prevent divergence at neutral loci is based on analysis of Gst. When there are significantly more than one migrant per generation, Gst is close to zero. But as we just saw, Gst can be close to zero even if the groups are completely diverged (no shared genes). So it is wrong to think that because there are more than one migrant per generation., divergence is necessarily low. Low Gst does not equal low divergence.

    A derivation in my 2008 Mol Ecol article shows that the quantity which controls divergence between a pair of groups at a given locus is the relative migration rate divided by the mutation rate. The relative migration rate (number of migrants divided by population size) might very well be small between many groups of humans.

    I don’t understand the math involved, but I thought I just pass this along.

  5. reiner Tor says:

    My favorite is when it’s argued that races don’t exist because there are huge genetic differences between populations within the same race, like between Greeks and Swedes. Yeah, mammals and reptiles are the same, because there are so huge differences between mice and elephants or between tortoises and crocodiles…

    • feministx says:

      Apparently the argument in the article referenced is that race does not exist because humans from different tribes/regions have a history of intermixing with each other. I guess if ethnicity does not exist, then ethnic differences cannot exist.

      Ok. Dog breeds don’t exist either. Social construct. It just so happens that these long haired dog resembling wolves are more effective at pulling sleds than these rat like dogs from mexico. Just different individual dogs being suited for different tasks.

      • TWS says:

        It’s because huskies practice pulling heavy loads. Hitch up Paris Hilton’s rat-dog to a hundred pound block and in no time he’ll be dragging it down the street. If that doesn’t work it’s obviously because of the stereotype threat and those racist huskies have the poor rat-dog convinced he can’t succeed.

      • reiner Tor says:

        Yeah, the chihuahua only needs ten thousand hours of practice in heavy load pulling.

  6. harpend says:

    Breathless announcements about fossil species and about sub-species are fodder for journalists but are otherwise pointless. Perhaps we should argue about whether blue and green are really different colors or the same color. Such an argument would have the same structure as arguments about fossil species and arguments about whether race is real or not.

    Greg, find something else to post or we will turn our readers’ minds into mush.

    • Dude, blue and green are just variants of teal. Everyone knows that.

    • reiner Tor says:

      Blue and green might be different colors, but both are equally valid and enrich our painting, and we shouldn’t impose our color on others.

    • feministx says:

      “Perhaps we should argue about whether blue and green are really different colors or the same color.”

      Some people mistakenly think that blue and green are determined. However, there is significant overlap in the wavelengths that reflect off blue and green substances. It is all mixed. Further, have you heard of the Lewontin blue/green hypothesis? If you turn the lights off both colors appear pure black. There is a complex interaction of retina perception and environmental light that affects perception of blue and green. Therefore, how can you say blue and green are distinct?

      • reiner Tor says:

        I think that believing that blue and green are wavelength-determined is pure paintism.

      • gcochran9 says:

        It’s all horseshit, if you ask me. In fact, it’s all horseshit even if you don’t ask me. People are trying to make population differences go away: it can’t be done, certainly not by arguing about classification issues.

      • reiner Tor says:

        Dr. Cochran, I think you are so full of paintist hate that your sarcasm-detectors stopped working.

    • Anonymous says:

      Could Floresian hobbits have been fertile with apes as well as humans? That possibility would create a problem for those arguing that the concept of race, blue, green and bleen, is a mere metaphysical ontology gone wild.

      Blue and green “Nominalists hold that universals are not to be included in our ontology, that they do not exist. All that exists are particular objects. We group them, not by virtue of their pertaining to one universal or another, but as a convention of language based on our perceptions of them. For example, we find that looking at a clear sky, a clean body of water and a lapis gives us a similar colour sensation; so we group them under the name blue.[…]
      Imagine that we were to come across a society of people, … that only had words for juxtaposed pairs of colours and instead of individual colours…. What would a realist say about such a society? It seems they will have to say that the new society has plainly missed the point: after all, on the realist account, the new society has merely failed to recognise the universals of blueness …. Does the difference in our ways of grouping rest on some superior knowledge of reality? … The Realist might try to object that there is in fact a form of the new society colour, bleen (a juxtaposition of blue and green), […]…[N]ominalism states that our grouping of objects and defining them thereby is just a convention of our language, there is no special relation of object to properties.” Philosophy professor trolling for relevance explains how the concept of race is all wrong on NYT Opinionator blog “metaphysical views of race on the one hand, which make it out to describe really existent kinds [‘Realism’], and normative views on the other, which take race to be useful in some way or other, but not real. ”

      “Scientists debunk race down, a la Lewontin’s argument: that there is as much genetic variation between two members of any supposed race, as between two members of supposedly distinct races, thus showing that “science gives the best description of what is real, with the rest counting as nothing more than epidermal illusion”. Philosophers debunk race up as ” constructed by language, society, perception, or events, so that only naïve, life-hating oppressors would insist on a “reality” hiding beneath the play of surfaces”

      The odds are fair that a modern human could successfully mate with a Floresian hobbit, assuming that it’s really an island-dwarfed version of Homo erectus. Even though it was three feet tall and had a chimp-sized brain. Somehow that doesn’t convince me that races and subspecies don’t exist.

      The assumption about the human species that the ‘all one species crowd” make is the same one they castigate the Western world for making about races: Essentialism. They’re assuming there are necessarily qualities that all members of the class ‘ the human species’ share,. Moreover they are asserting that they have a privileged access to the those essential properties, shared by all the members of the the species that includes humans. It so happens that species like Homo habilis that could be fertile with modern humans died out, but if Floresian hobbits and some other extinct species were still around, they would constitute an unbroken chain of fertility between apes and humans, and what are now regarded as separate species would be in a single species that included modern humans, even though the extremes of the species (apes and humans) would not be fertile with each other. If that was in fact the case I suppose an existentialist view of ‘Race’ (the modern human race) would become a very popular concept.

  7. So Wolpoff suggests that something that has happened far less than 1% of the matings – hell, less than .0001%, I’m roughing out, back of the envelope – but has happened for a long time, is thus “normal.” I suspect he is deeply influenced by the fact that 21st C humans think it’s cool.

    Unfortunately for the advance of knowledge, the coolness of an idea does seem to count, even among scientists.

  8. dearieme says:

    The result of a Milford mating with a Wolpoff was pretty unfortunate, don’t you think?

  9. Rum says:

    When a Neanderthal bred with a non-Neanderthal the resulting child was not 3-4 % N. but 50%. Those offspring were valued by the mom and the clan or none of them would have survived. This strongly suggests that Neanderthals and the others could understand each other and see value in each others qualities. I was not there, but I make the assumption that successful child raising was a group endeavor.

    • reiner Tor says:

      It is possible that they were despised, and as a result the vast majority of such children perished. It was enough for a few such children to survive and mate with fully AMHs, the quarter Neanderthal grandchildren probably looked somewhat different but already AMH enough to pass as almost full-blooded AMHs, they could now also get support from AMH relatives on both sides. One more generation and the problem almost fully disappeared. So such half-breeds only had a problem for one or at most two generations, I guess one eighth Neanderthals looked just slightly different from a full AMH. It is also likely that only the very best and brightest Neanderthal half-breeds (with the best social skills etc.) could survive, thus ensuring that only the very best and most useful of the Neanderthal genes entered the AMH gene pool.

      • Rum says:

        If the vast majority of a rarely occurring hybrid failed to survive, where does 2-4% of modern euro-genes come from?

      • reiner Tor says:

        I guess those are the genes which had selective advantages, so once surviving the first few generations, they spread in the population.

      • dave chamberlin says:

        It is accepted that we are 2 to 4% Neanderthal, excluding the subsaharan Africans. For at least a brief period then incredibly infrequent matings between Neanderthals and anatomically modern humans wasn’t the case for that small group from which we humans living north of the Sahara have all descended. It would be the accepted common explanation placed in all the history books that discuss human evolution that this hybridization event was the key to our taking “the great leap forward.” But noooooo, small groups of eggheads must gather in obscure blogs to mention this terrible notion for fear of banishment from polite society, forever branded as evil hateful racists. In the meantime it’s fun to be a gadfly.

  10. TWS says:

    Have there been any studies of fertility between our nonexistant races? Fertility clinics might be a place where such research could be helpful.

    Of course, since eskimoes are just like bushmen even asking this question is offensive, racist, and ridiculous.

    • Sideways says:

      My wife (interracial marriage) had an extremely unusual immune response when she gave birth to our child (not one the doctors had seen before from this cause). Didn’t rise to the level of causing infertility between us before modern medicine, but it does have me wondering if we were part way there.

  11. Can medicines tailored to different evolutionary histories produce dramatically improved health outcomes?

    http://en.wikipedia.org/wiki/Isosorbide_dinitrate/hydralazine

    Yes.

    Would lots of examples be found if people looked for them?

    Dunno. I’d guess yes.

    *If* lots of examples of medicines producing dramatically improved health outcomes were looked for and found then how big a deal would (lots) * (dramatically improved) be?

  12. Pingback: linkfest – 10/20/13 | hbd* chick

  13. Anonymous says:

    Hmmm…John Hawks is a notable student of Milford Wolpoff…

  14. Jim says:

    Retreating into the fog of philosophical scepticism is a tactic adopted by those who no longer have a convincing factual argument.

    • Anonymous says:

      Well it’s not just races the the bundling of properties argument is used against the existance of apples ect … everything.

      A different tack against nasty science facts is the “Evolutionary argument against naturalism [which holds] that the combination of evolutionary theory and naturalism is self-defeating on the basis of the claim that if both evolution and naturalism are true, then the probability of having reliable cognitive faculties is low. ”
      So we may be being systematically misled about races–which may be just part of a wider indeterminate flow of genes–by our cognitive faculties; because they’re working towards the goal of reproductive fitness, not discovering the truth.

  15. Francois says:

    Just saw that Larry Arnhart said that Cochran “misses the whole point of the Lordkipanidze et al. article”. See comments:

    http://darwinianconservatism.blogspot.com/2013/10/a-complete-adult-hominid-skull-from.html

    Arnhart is a weird guy. He calls himself a “Darwinian conservative” but when it comes to race and evolution and Arnhart largely and uncritically parrots the Cultural Marxist line on race.

  16. Anonymous says:

    I beieve a study showed that those having most grandparental ancestry from different countries had least reproductive fitness Dawkins wrote about it. the Extended Phenotype I hink

    Arnhart doesn’t seem to be taking the repruductive fitness of the hybridisation into account. I think the extreme of the ranges of sub(species) is where the hybridisation would occur, unless they occupied different niches–which suggests one could be prey for another. So mostly sub(species) would not be in meaningful geographical contact . Where they lived in propequity.
    one species might have avoided contact .

    Where there was contact and they mated the reproductive fitness of the resultant offspring could be higher or lower. If it was lower the hybrids could have disappeared . It seems to me if there was all this fairly successful hybridisation what should be trumpeted by all one species proponents is the ubiquity of resultant MIXED populations.

  17. Pingback: Links 10/27/13 | Mike the Mad Biologist

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