Another Neandertal paper in Proceedings of the Royal Society B. But, because there is a delay between when the press is released to talk about it, and when it goes live, I haven’t gotten a look at the primary material. There’s a lot of juicy stuff in this piece at NBC Science though, Brain comparison suggests that Neanderthals lacked social skills. The two scientists giving quotes, Chris Stringer and Robin Dunbar, know their stuff (one of Dunbar’s graduate students also contributed heavily). In case you don’t know Stringer, he is the paleoanthropologist who was most forceful in pushing for the “Out of Africa” model. Dunbar is the popularizer of Dunbar’s number. I’m assuming Stringer brings the anatomy to the game, while Dunbar frames the bigger theoretical picture. Basically the morphology of the cranium implies that Neandertals may have allocated more of their cognitive capacity to vision and coordination, and less to social activities (because there’s not as much room for the latter). This explains how Neandertals could have a larger cranial capacity than modern humans (they did, though so did Ice Age modern humans) but be somewhat less “intelligent” than us (regular readers know I’m not a big fan of scare quotes for intelligence, but in this case I think it’s warranted).
A month ago I posted Don’t trust an archaeologist about genetics, don’t trust a geneticist about archaeology, in response to James Fallows at At 5% Neanderthal, You Are an Outlier. Fallows has now put up a follow up, The Neanderthal Defense Committee Swings Into Action, where he links to my response post. This prompted the original archaeologist in question to reach out to me via email. I am posting the letter, with their permission, below.
If you have a hard time following all the Neandertal genomics findings from the last few years, and their implications, National Geographic has a really thorough piece up. It’s a good digest of all the news you can use. One thing I would like to add: from what I can tell the probability of the signals of admixture in non-Africans being genuinely Neandertal seem to be increasing as we progress. In other words, you should weight the “other side” (ancient population structure, where some African populations were closer to Neandertals before they left Africa) less than you did in 2010.
Of course one of the more inevitable aspects of the admixture story has been the humanization of Neandertals. I don’t know how I feel about this. Should our own affinity to Neandertals alter our view of their behavior or anatomy? Plenty of behaviorally anatomically modern humans were beastly after all.
John Hawks prompts to reemphasize an aspect of my thinking which has undergone a revolution over the past 10 years. I pointed to it in my post on the Khoe-San. In short, the common anatomically modern human ancestors of Khoe-San and non-Khoe-San may not have been people. Rather, people may have evolved over the past 100-200,000 years ago. Of course the term “people” is not quite as scientific as you might like. In philosophy and law you have debates about “personhood”. Granting the utility of these debates I am basically saying that the common ancestor of Khoe-San and non-Khoe-San may not have been persons, as well understand them. Though, as a person myself, I do think they were persons. At this point I am willing to push the class “person” rather far back in time.
As I suggested earlier there is an implicit assumption that personhood is a shared derived trait of our species. Or at least it is a consensus today that all extant members of H. sapiens are persons. Since Khoe-San are persons, the common ancestor of Khoe-San and non-Khoe-San must also be persons if personhood is a shared derived trait. But, we also know that there are many aspects of realized personhood on a sociological or cultural scale which seem to diminish the further back in time you go. For example, the Oldowan lithic technology persisted for ~1 million years. A common modern conception of persons is that persons in the aggregate are simply never so static. Persons have culture, and culture is protean. Therefore, one might infer from the nature of Oldowan technological torpor that the producers of that technology were not persons.
Last August I had a post up, The point mutation which made humanity, which suggested that it may be wrong to conceive of the difference between Neanderthals and the African humans which absorbed and replaced them ~35,000 years ago as a matter of extreme differences at specific genes. I was prompted to this line of thinking by Svante Pääbo‘s admission that he and his colleagues were searching for locations in the modern human genome which differed a great deal from Neanderthals as a way through which we might understand what makes us distinctively human. This sort of method has a long pedigree. Much of the past generation of chimpanzee genetics and now genomics has focused on finding the magic essence which differentiates us from our closest living relatives. Because of our perception of massive phenotypic differences between H. sapiens and Pan troglodytes the 95-99% sequence level identity is thought by some to be perplexing. Therefore models have emerged which appeal to gene regulation and expression, or perhaps other forms of variation such as copy number, to clear up how it can be that chimpanzees and humans differ so much. Setting aside that the perception of difference probably has some anthropocentric bias (i.e., would an alien think that chimpanzees and humans are actually surprisingly different in light of their phylogenetic similarities? I’m not so sure), it doesn’t seem to be unreasonable on the face of it to plumb the depths of the genomes of hominids so as to ascertain the source of their phenotypic differentiation.
But can this model work for differentiating different hominin lineages? Obviously there’s going to be a quantitative difference. The separation between chimpanzees and modern humans is on the order of 5 million years. The separation between Neanderthals and modern humans (or at least the African ancestors of modern humans ~50,000 years B.P.) is on the order of 500,000 years. An order of magnitude difference should make us reconsider, I think, the plausibility of fixed differences between two populations explaining phenotypic differences.
“There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare [children] to them, the same [became] mighty men which [were] of old, men of renown.”
The Pith: Pygmies and Khoisan have admixture from a distinct population at the level of ~2%. This population diverged from the other ~98% of their ancestry ~700,000 years before the present, and the hybridization occurred ~30-40,000 years before the present. Most other African groups have only traces of this element, with some West Africans lacking it.
I have read the paper in PNAS which I referred to below. There isn’t that much I can add at this point. A lot of the guts were pushed into the supplements, which aren’t on the web yet. I was correct that the Mbuti Pygmies of the eastern Congo likely have a special place in this possible admixture event. In particular, they seem to possess the diverged variants found in the western Pygmies, the Biaka, and the Khoisan populations of southern Africa. As assumed the pattern of admixture seems to be such that the two Pygmy groups and the Khoisan exhibit elevated signatures of archaic contributions, while other African groups manifest admixture in direct proportion to their known admixture to the aforementioned populations. For example, the Bantu group with the highest proportion of admixture are the Xhosa, who also have the most Khoisan ancestry of non-Khoisan populations. The West African Mandenka seem to have trivial admixture from this archaic group. What does this mean?
Steve Hsu points me to a piece in The New Yorker on the science and personality of Svante Pääbo. The personality part includes references to Pääbo’s bisexuality, which to me seemed to be literally dropped into the prose to spice it up. Of course it was the science which I found interesting. There are many more bisexuals than there are heterodox scientists. And yet like many researchers of yore it seems that Pääbo is out to find the genes which make humanity distinctive as we understand it (if the reporting is accurate, which I don’t take as a given). There are some interesting tantalizing clues littered about; some genes implicated in autism seem to exhibit Neandertal vs. modern human differences (with the Neandertals carrying the autism-implicated variants).
John Hawks weighs in on the paper I pointed to yesterday. As someone who couldn’t make heads or tales of the stratigraphy I’m a little relieved that John took time out from his tour of Rome to comment. Not too surprisingly it seems that the relatively definitive seeming conclusion of the study authors, and especially the hyping in the press releases, should probably not be taken at face value.
When the draft sequence of the Neandertal genome was analyzed it turned out that there was little difference across non-Africans in their proportion of admixture from this other human lineage. It was a rather strange finding as Neandertals seem to have flourished from Europe to the Altai, and from the ice sheets to the fringes of the Middle East. If Papuans had Neandertal admixture the logical conclusion was that that had to occur in the Middle East. Additionally, if Europeans didn’t have much more Neandertal admixture than Papuans, that means that after the initial absorption the modern humans simply swept the field as they pushed north and west.
But there’s a little problem here: the archeology indicates that Neandertals survived for nearly ten thousand years in Europe after the first arrival of moderns. So the necessary conclusion granting all the above is that after the initial hybridization some barrier prevented further leakage of Neandertal genes into Europeans (or, perhaps modern Europeans descend from recently arrived Middle Eastern farmers who lack the full Neandertal complement of Paleolithic Europeans?).
A new paper in PNAS overturns these paradoxes by re-dating the last Neandertals, allowing them to melt away rather quickly ~40,000 years B.P., just as modern humans were sweeping across Eurasia. Revised age of late Neanderthal occupation and the end of the Middle Paleolithic in the northern Caucasus:
Mr. James Winters at A Replicated Typo pointed me to a short hypothesis paper, Neanderthal-human Hybrids. This paper argues that selective mating of Neandertal males with females of human populations which had left Africa more recently, combined with Haldane’s rule, explains three facts:
- The lack of Neandertal Y chromosomal lineages in modern humans.
- The lack of Neandertal mtDNA lineages in modern humans.
- The probable existence of Neandertal autosomal ancestry in modern humans.
If you don’t know, Haldane’s rule basically suggests that there’s going to be some sort of breakdown in the heterogametic sex. In humans females are homogametic, XX, and males are heterogametic, XY. The breakdown need not be death (or spontaneous abortion). It could be sterility (e.g., some mutation or genetic incompatibility which results in the malfunctioning of the flagella of sperm would do it).
So you have a scenario where only Neandertal males are interbreeding with the intrusive groups from the south. The hybrids from these pairings would then lack Neandertal mtDNA, since mtDNA is passed only from mothers. But the male offspring would have Neandertal Y chromosomes. This is where Haldane’s rule kicks in: these males in their turn would not reproduce. Therefore only the female hybrids would pass on their genes. These females obviously don’t pass on a Y chromosome. And, they would pass on their non-Neandertal mother’s mtDNA.
Mitochondrial DNA from 147 people, drawn from five geographic populations have been analysed by restriction mapping. All these mitochondrial DMAs stem from one woman who is postulated to have lived ab7out 200,000 years ago, probably in Africa. All the populations examined except the African population have multiple origins, implying that each area was colonised repeatedly
And so was published in the year 1987 the paper which established in the public’s mind the idea of mitochondrial Eve, which gave rise to a famous cover photo in Newsweek. This also led to the Children of Eve episode on the PBS documentary NOVA. Here is the summary:
NOVA examines a controversial theory that traces our ancestry to a small group of women living in Africa 300,000 years ago.
As Milford Wolpoff has complained it is probably accurate to characterize the documentary as not particularly “fair & balanced.” Mitochondrial Eve may have been controversial, and subsequently plagued by issues of molecular clock calibration as well as spurious interpretations of the cladograms, but the tide of history was on its side, and PBS was telling that story. And the story was not just the primary science, rather, one had to understand the controversy in light of the debates among paleontologists and between paleontologists and molecular biologists. A group of researchers, spearheaded by Chris Stringer argued for the recent origin of modern humans from Africa on the basis of fossils alone. They were challenged by an established school of multiregionalists who argued for deeper roots of modern human populations, which derived from local hominins which diversified after the the migration of H. erectus out of Africa. The argument of the multiregionalists was that selective sweeps across the full range of the human populations gave rise gradually to modern humanity as we know it, a compound of specific ancient local features and trans-population characters which unified us into a broader whole. Stringer and company presented a simpler model where anatomically modern human being arose ~200,000 years ago in Africa, and subsequently expanded to other parts of the world, by and large replacing the local hominin populations. In the multiregionalist telling Neandertals became human beings, while Out of Africa would imply that Neandertals were replaced by human beings.
I just purchased a copy of William Golding’s The Inheritors. Golding is famous for writing Lord of the Flies, a work of literature of such influence that it has made the transition into our everyday lexicon. But I just listened to a podcast of an interview with a biographer of the great author, and it seems that Golding and many of his admirers who are “close readers” judge The Inheritors as his finest novel.
The general outline of the plot is easy enough to find on Wikipedia, it is one of those stories about the transition from a “bushy” hominin tree of life to the dominance of H. sapiens sapiens. Neandertals are finally expiring as a species in the face of the advance of modern humans, who marginalize and extirpate all those who came before. But I get the impression that the execution of Golding’s attempt is very different from Clan of the Cave Bear. Not having read the book yet I do not know if William Golding’s depiction is up to snuff with the latest scholarship on the Neandertals (granted, I am not up to date on the latest scholarship on Neandertals!), though he did guess correctly in all likelihood as to their pigmentation. But, in light of the highly probable non-trivial Neandertal ancestry in over 80% of humans, I feel like revisiting Golding’s vision in the near future, as we carry within our genomes the shadows of both the inheritors and the dispossessed.
John Hawks has a very long post up. This part caught my attention:
We don’t really know the answers, but now we have a chance to test hypotheses about ancient population size and expansion in Neandertals. My point at the moment is only this: If today Neandertal genes make up only one percent of the gene pool of the 5 billion people outside Africa, that’s the genetic equivalent of 50 million Neandertals.
As Hawks notes later, this paper comes pretty close to resolving whether Neandertals were of the same species as we moderns, at least using the biological species concept. There were fertile hybrids. That should not be too surprising, a few years ago when the Neandertal introgression story was big I looked into mammalian embryology, and our lineage had to be very special as mammals went for their to be inter-population sterility.
This is not just a science story. Dave Chamberlain observes:
Anyone else notice that the artists depictions of neanderthals have slowly changed from stupid brute monkey men to ruggedly handsome moderns with a protruding brow? Hmmm, I bet they get even more good looking now. Hawks promises all neanderthals all the time, I for one can’t get enough of it.
I think that this will change our perceptions, and “artists’ renderings” quite a bit. A few years ago when it seemed that Neandertals may have been highly depigmented I observed that it was a bit strange that in most depictions they tended to be rather dark and swarthy as Europeans go (most famously in Jean Auel’s work the H. sapiens sapiens were Aryan Übermensch while the Neandertals were small and dark). I think some of the same subconscious dynamic was at play as when Tom Coburn was outraged at the TV nudity of Schindler’s List. Coloured people naked on a National Geographic special is one thing, but white people should be decent! (and please, don’t accuse me of seeing racism where it isn’t. If you know me you know that I’m not super-obsessed with that sort of thing, but I think it’s pretty obvious that there’s a lot of implicit assumptions which go into being a white European, and how one views someone and how they should behave)
Good time to be alive, no?
Update: John Hawks.
Update II: Science got the page up.
The topline is this, researchers presented the following at the recent meeting of the American Association of Physical Anthropologists:
* An analysis of 614 highly variant loci, microsatellites, in ~2,000 people from diverse populations imply some variants which seem to be derived from human lineages outside of the mainline which led to the anatomically modern humans who left Africa 50-100,000 years before the present to settle the world. I assume there were “long branches” on the phylogenies of some loci, indicating that some of the alleles were “separated” from others for long periods of time so that recombination wasn’t able to dissolve the differences between distinctive haplotypes (if we’re all descended from a small African populations which expanded demographically less than 100,000 years ago the common ancestor of the variants should have a shallow time depth).
* The data imply two admixture events, one 60,000 years ago in the eastern Mediterranean, the other 45,000 years ago in East Asia. I think of this as a floor to the number of events. The latter one seems particularly clear in Oceanic populations from the reporting.
* African populations do not have the variants for these two admixture events (there hasn’t been that much back migration to Africa aside from north of the Sahara and the Horn of Africa. I assume that’s because Africans are well adapted to their environment, and outsiders are not).
In light of the recent discovery of a Siberian hominin which lived ~30,000 years ago, and was not a H. sapiens sapiens or H. sapiens neanderthalis, as well as the confusing but intriguing Hobbits of Flores, I think we can conclude that the the evolutionary genetic past was much more complicated than we’d assumed 10 years ago. Remember three years ago when there was a spate of research on a few genes which were suggestive of introgression into the human genome from Neandertals? There are other hints here and there which pop up in the literature over the years, some in Asia. But the methods being imperfect, and interpretation being somewhat an art, a consensus of Out-of-Africa + total replacement has been assumed to be a null. So we look at isolated results with some skepticism (I think this is justified).
So is this going to be met with skepticism due to reliance on the orthodox model? This section of the article is intriguing: