Yesterday I pointed to a paper which was interesting enough, but didn’t pass the smell test in relation to other evidence we have (at least in my opinion!). A primary concern was the fact that uniparental (male and female lineages) show a peculiar distribution of variation in comparison to autosomal genetic variation (i.e., the vast majority of the genome) in the case of Europe (genome-wide analysis suggest more of Europe’s variation is partitioned north-south, but Y and mtDNA results often imply an east-west split). But a secondary concern I had was that I felt the models were a bit too stylized. In particular following Cavalli-Sforza and Ammerman the authors concluded that demic diffusion better fits their results of genetic variation in Europe (as opposed to continuity of Paleolithic hunter-gatherers). This is likely correct, but these are not the only two models.
A paper out in Nature Communications, using analysis of the phylogenetics of whole ancient mitchondrial genomes, outlines my primary concern when it comes to the models being tested, Neolithic mitochondrial haplogroup H genomes and the genetic origins of Europeans:
Haplogroup H dominates present-day Western European mitochondrial DNA variability (>40%), yet was less common (~19%) among Early Neolithic farmers (~5450 BC) and virtually absent in Mesolithic hunter-gatherers. Here we investigate this major component of the maternal population history of modern Europeans and sequence 39 complete haplogroup H mitochondrial genomes from ancient human remains. We then compare this ‘real-time’ genetic data with cultural changes taking place between the Early Neolithic (~5450 BC) and Bronze Age (~2200 BC) in Central Europe. Our results reveal that the current diversity and distribution of haplogroup H were largely established by the Mid Neolithic (~4000 BC), but with substantial genetic contributions from subsequent pan-European cultures such as the Bell Beakers expanding out of Iberia in the Late Neolithic (~2800 BC). Dated haplogroup H genomes allow us to reconstruct the recent evolutionary history of haplogroup H and reveal a mutation rate 45% higher than current estimates for human mitochondria.
The above is a graph which illustrates phylogenetic relationships using the TreeMix package. It is from the paper I alluded to yesterday. The paper, DNA analysis of an early modern human from Tianyuan Cave, China, is open access, so everyone should be able to read it. Its mtDNA analysis shows that the Tianyuan sample, from the region of Beijing and dating to ~40,000 years B.P., is a basal clade in haplogroup B, which is common in eastern Eurasia and the New World. This is a satisfying result insofar as the understanding in relation to this haplogroup is that it diversified ~50,000 years B.P. There is very strong support in these data for the proposition that Tianyuan forms a distinct clade with the populations you see above, as opposed to western Eurasians. This is important because this sample seems to date with relatively good precision to 40,000 years B.P., supporting the archaeological contention that modern humans were already diversifying into western and eastern lineages 40-50,000 years ago. In contrast statistical genomic inferences tend toward a lower date for divergence. We can be moderately confident at this point that some aspect of the west-east divergence predates subsequent later gene flow events, which might lead to confusing archaeology-blind methods.
I recently inquired if anyone was sequencing Cheddar Man. In case you don’t know, this individual died ~9,000 years ago in Britain, but the remains were well preserved enough that mtDNA was retrieved from him. He was of haplogroup U5, which is still present in the local region. Cheddar Man is also particularly interesting because he is definitely a Paleolithic hunter-gatherer, predating the Neolithic in Britain by thousands of years.
It turns out that no one is looking at Cheddar Man now. But that’s probably because money and time are finite. I was told that there are plenty of other specimens which would also probably be good candidates for sequencing in the Museum’s collection (this doesn’t seem to be a case where curators are being stingy and overprotecting of their specimens). That’s not too surprising. We’ll probably answer a lot of questions about the roles of demographic diffusion vs. cultural diffusion when it comes to agriculture soon enough (as in, over the next 10 years as techniques for getting signal out of old degraded and contaminated samples get better).
We now have G2a3 from Neolithic Linearbandkeramik in Derenburg and G2a in Treilles in addition to Ötzi from the Alps. G2a folk got around. He joins Stalin and Louis XVI as a famous G2a.
It was already clear with the discovery of G2a in France and Central Europe, that this otherwise uncommon present-day haplogroup in Europe was more prominent during the Neolithic, and Ötzi’s data point seals the case.
In a sense, the triple G2a finds in Neolithic Europe confirm the origins of the European Neolithic population in West Asia, but renew the mystery as to how all the rest of the “players” of the European Y-DNA scene appeared on the scene, with everything except G and I first appearing in the ancient DNA record after the end of the Neolithic.
Yes, I believe that the Paleolithic-Neolithic dichotomy is more hindrance than help in understanding the European past (the Paleolithic itself may have exhibited more population turnover than we can appreciate). I suspect that the two most common European Y haplogroups, R1a and R1b, underwent rapid increase in frequency over the past ~5,000 years. I do not believe that this is necessarily representative of the rest of the genome. The spread of male lineages can be rather unrepresentative.
In other news, Ötzi’s genome is going to drop any day now. My prediction that it’s more West Asian than we might have expected seems more plausible, though less surprising and risky, at this point.
Image credit: 23andMe
Ewen Callaway has a good survey of what’s been going down in ancient human genomics over the past year in Nature, Ancient DNA reveals secrets of human history. It’s not paywalled, so read the whole thing. Most of it won’t be too surprising for close readers of this weblog, but this part is new:
By comparing individual DNA letters in multiple modern human genomes with those in the Neanderthal genome, the date of that interbreeding has now been pinned down to 65,000–90,000 years ago. Montgomery Slatkin and Anna-Sapfo Malaspinas, theoretical geneticists from the University of California, Berkeley, presented the finding at the Society for Molecular Biology and Evolution meeting in Kyoto, Japan, held on 26–30 July.
Slatkin says that their result agrees with another study presented at the meeting that came from the group of David Reich, a geneticist at Harvard Medical School in Boston, Massachusetts, who was involved in sequencing both the Neanderthal and Denisova genomes. The dates also mesh with archaeological finds bookending early human migrations out of Africa to between about 50,000 and 100,000 years ago. Reich’s team is now developing tools to find signs of more recent interbreeding that might have occurred after humans arrived in Asia and Europe.
Remember that the Neandertal admixture seems present in all non-Africans. That pegs the admixture event very early, before the diversification of modern human populations. I wouldn’t put too much stock in any one value presented at a conference with a large confidence interval. From what I hear there will be much more on statistical genetic inferences of admixture timing over the next year, but if there’s one thing that the enormous yield from genomes constructed from ancient DNA has convinced me is that we should be really cautious of results which we can’t cross-check easily because of their time depth. I read a lot of papers by high-powered teams before 2010 on how the genomic evidence implied no admixture between modern human and archaic lineages, and gave them great weight. There’s only so much power in working back to the past from the present.
Also at the meeting, researchers led by geneticist Angela Graefen of the Institute for Mummies and the Iceman reported that they have succeeded in sequencing the Iceman’s whole genome, despite the highly fragmented nuclear DNA. The genome has already revealed some surprises. One preliminary finding shows that the Iceman probably had brown eyes rather than the blue eyes found in many facial reconstructions done by artists. Graefen and her colleagues are also examining the DNA to see if Ötzi possessed genetic predispositions to diseases such as arthritis, which other researchers have diagnosed based on radiological and other evidence.
I’m assuming we’ll know a whole lot more before the end of summer. So I’m going to go out on a limb and make a prediction based on what I suspect about the southern European genetic landscape ~5,000 years ago: Ötzi will be more like contemporary West Asian people, Georgians, Armenians, etc., than modern north Italians and south Germans are. Right or wrong, I hope the results will be interesting!
Seriously, sometimes history matches fiction a lot more than we’d have expected, or wished. In the early 2000s the Oxford geneticist Bryan Sykes observed a pattern of discordance between the spatial distribution of male mediated ancestry on the nonrecombinant Y chromosome (NRY) and female mediated ancestry in the mitochondrial DNA (mtDNA). To explains this he offered a somewhat sensationalist narrative to the press about possible repeated instances of male genocide against lineage groups who lost in conflicts.
Here is a portion of the book of Numbers in the Bible:
15 – And Moses said unto them, Have ye saved all the women alive?
16 – Behold, these caused the children of Israel, through the counsel of Balaam, to commit trespass against the LORD in the matter of Peor, and there was a plague among the congregation of the LORD.
17 – Now therefore kill every male among the little ones, and kill every woman that hath known man by lying with him.
18 – But all the women children, that have not known a man by lying with him, keep alive for yourselves.
Then there is the rape of the Sabine women. The ethnogenesis of the mestizo and mulatto populations of the New World in large part was the union between non-European women and European men. These are hard brutal myths and hard brutal facts. But do they reflect an essential aspect of the dynamics which have shaped our species’ past?
I’m not willing quite yet to add a confident weight upon this possibility, but this seems to be part at least part of the picture. You see a major disjunction on male and female lineages among South Asians for example. A new paper in PNAS adds weight to this possibility, albeit only incrementally. Ancient DNA reveals male diffusion through the Neolithic Mediterranean route:
After 2010′s world-shaking revolutions in our understanding of modern human origins, the admixture of Eurasian hominins with neo-Africans, I assumed there was going to be a revisionist look at results which seemed to point to mixing between different human lineages over the past decade. Dienekes links to a case in point, a new paper in Molecular Biology and Evolution, An X-linked haplotype of Neandertal origin is present among all non-African populations. The authors revisit a genetic locus where there have been earlier suggestions of hominin admixture dating back 15 years. In particular, they focus on an intronic segment spanning exon 44 of the dystrophin gene, termed dys44. Of the haplotypes in this they suggested one, B006, introgressed from a different genetic background than that of neo-Africans. The map of B006 shows the distribution of the putative “archaic” haplotype from a previous paper cited in the current one from 2003. As you can see there’s a pattern of non-African preponderance of this haplotype. So what’s dystrophin‘s deal? From Wikipedia:
Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. This complex is variously known as the costamere or the dystrophin-associated protein complex. Many muscle proteins, such as α-dystrobrevin, syncoilin, synemin, sarcoglycan, dystroglycan, and sarcospan, colocalize with dystrophin at the costamere.
Dystrophin is the longest gene known on DNA level, covering 2.4 megabases (0.08% of the human genome) at locus Xp21. However, it does not encode the longest protein known in humans. The primary transcript measures about 2,400 kilobases and takes 16 hours to transcribe; the mature mRNA measures 14.0 kilobases….
Dystrophin deficiency has been definitively established as one of the root causes of the general class of myopathies collectively referred to as muscular dystrophy. The large cytosolic protein was first identified in 1987 by Louis M. Kunkel…after the 1986 discovery of the mutated gene that causes Duchenne muscular dystrophy (DMD) ….
OK, so we’ve established that this is not an obscure gene. Here’s the abstract of the new paper:
I predicted earlier that Hobbit DNA would be extracted in 2011. It was pretty much an educated guess based on various omissions I sensed in papers in 2010. But it seems that an attempt is going to be made:
Scientists are planning an attempt to extract DNA from the ‘hobbit’ Homo floresiensis, the 1-metre-tall extinct distant relative of modern humans that was unearthed in Indonesia, following a study that suggests problems in standard sampling methods in ancient-DNA research could have thwarted previous efforts.
This year, geneticists at the Australian Centre for Ancient DNA (ACAD) at the University of Adelaide hope to recover DNA from a roughly 18,000-year-old H. floresiensis tooth, which was excavated in 2009 from the Liang Bua site on the Indonesian island of Flores.
No guarantees, but still exciting.
When it comes to the synthesis of genetics and history we live an age of no definitive answers. L. L. Cavalli-Sforza’s Great Human Diasporas would come in for a major rewrite at this point. One of the areas which has been roiled the most within the past ten years has been the origin and propagation of the agricultural lifestyle across the European continent between 10,000-6,000 years before the present (starting in Europe’s southeast fringe a few thousand years after the origination of the Neolithic lifestyle in the Levant, and finally pushing into the southern Scandinavian peninsula only ~6,000 years ago). The reasons for this particular debate about the origin of the European are manifold. First, most scholars are of European ancestry, and some of the debates have roots going back a century. So a natural interest exists based on normal human biases. Second, when it comes to genetics the climate of Europe is ideal for the preservation and extraction of ancient DNA. Third, there are relatively clear and distinct theoretical models which can be tested by the data, whether to verify or refute.
I have already reviewed earlier work in three previous posts, European man perhaps a Middle Eastern farmer, European man perhaps not a Middle Eastern farmer, and Völkerwanderung back with a vengeance. Instead of rehashing everything I’ll take it as a given that you’ve read or skimmed those posts. Rather, let’s move on to a new paper in PLoS Biology, Ancient DNA from European Early Neolithic Farmers Reveals Their Near Eastern Affinities:
Genetics is now being brought to bear on whether there were non-trivial population movements in the prehistorical period. Or more precisely, a combination of genetics and archaeology, whereby the archaeologists retrieve and extract genetic material which the geneticists amplify and analyze. This has helped establish that European hunter-gatherers were not lactase persistent. This is totally unsurprising, but was a nice proof of principle. When it comes to ascertaining genetic relationships among populations, as opposed to specific traits whose genetic architecture is well established, it’s a bit trickier. Who knows how many population movements may have interposed themselves between the present and a particular period in the past from which you have samples?
A new paper in PLoS ONE reports findings which do little to clarify, though add weight to skepticism as to the definitiveness of earlier results, Genetic Diversity among Ancient Nordic Populations:
Jared Diamond famously argued in Guns, Germs and Steel that only a small set of organisms have the characteristics which make them viable domesticates. Diamond’s thesis is that the distribution of these organisms congenial to a mutualistic relationship with man shaped the arc of our species’ history and the variation in wealth that we see (though his a human-centric tale, we may enslave them, eat and use them as beasts of burden, but these are also species which have spread across the world with our expansion). This thesis has been challenged, but the bigger point of putting a focus on how humans relate to their domesticated animals, and the complex co-evolutionary path between the two, is something that we need to consider. In a plain biological and physical sense animals have utility; we eat them, and for thousands of years they were critical to our transportation networks. Some have argued that the rise of Islam, Arab monotheism, was contingent on the domestication of the camel (which opened up interior trade networks previously unaccessible). In The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World the argument is made that the distribution of the Indo-European languages has to do with the facility of Central Eurasian plainsmen with their steeds. And of course there is the domestic dog, arguably the one creature which is able to read our emotions as if they were a con-specific.
I suspect that the evolution and ethology of domesticated animals will offer a window into our own evolution and ethology. Konrad Lorenz famously believed that humans were going through their own process of domestication all the while that they were selecting organisms suited to their own needs. More pliable, less intelligent, faster growing and maturing, and so forth. Know thy companions, and know thyself, so to speak.
What about an animal as intelligent as a dog, but famously tasty? (the combination of the two characters causing some ethical tension in the minds of many) I speak here of the pig. A few years ago research came out which showed that pig-culture was introduced to Europe from the Middle East. That is, Middle Eastern pigs came with Middle Eastern people in all likelihood. But modern European pigs do not derive from these lineages, rather, by comparing modern genetic variation with ancient DNA the authors showed that the Neolithic pigs had been replaced by local breeds. Just as pigs can go feral and fend for themselves rather easily, it seems that their basic morph can be derived from wild boar populations easily as well (by contrast, it will perhaps take some effort to derive a pekingese from wolf populations, offering a reason for why small dogs seem to have emerged once). A new paper explores the evolutionary history and phylogeography of the pigs of the swine-loving societies par excellence, those of East Asia. Patterns of East Asian pig domestication, migration, and turnover revealed by modern and ancient DNA: