Spread of farming in Europe. Cultural diffusion or population replacement? SourceBetween 9,000 and 3,000 years ago farming spread through Europe and replaced hunting, fishing, and gathering. Was this process just a change in lifestyle? Or was it also a population change? Did Middle Eastern farmers replace native Europeans?
For Greg Cochran, the answer is clear:
Increasingly, it looks as if the hunter-gatherers who lived in Europe at the end of the ice age have been largely replaced. Judging from all those U5 mtdna results from ancient skeletons, I’d say that the hunters don’t account for more than 10% of the ancestry of modern Europeans. (Cochran, 2011)
Actually, the U5 haplogroup remained common after the transition to farming. This was the conclusion of a study of 92 Danish human remains that ranged in time from the Mesolithic to the Middle Ages. The study found genetic continuity from late hunter/gatherer/fishers to early farmers:
The extent to which early European farmers were immigrants or descendents of resident hunter-gatherers (replacement vs. cultural diffusion) has been widely debated, and new genetic elements have recently been added. A high frequency of Hg U lineages , especially U5, has been inferred for pre-Neolithic Europeans based on modern mtDNA data, with Hg U5 being fairly specific to Europe. [...] Our study therefore would point to the Early Iron Age and not the Neolithic Funnel Beaker Culture as suggested by Malmstrom et al. (2009), as the time period when the mtDNA haplogroup frequency pattern, which is characteristic to the presently living population of Southern Scandinavia, emerged and remained by and large unaltered by the subsequent effects of genetic drift (Melchior et al., 2010)
Thus, the sharp genetic divide was not between late hunter/fisher/gatherers and early farmers. It was between the earliest farmers and groups that had been farming for at least a millennium or so. The evidence is more consistent with natural selection than with population replacement.
But isn’t mtDNA unresponsive to natural selection? That’s what I used to think. There is growing evidence, however, that some mtDNA loci respond to natural selection. In particular, some haplogroups seem to reflect a trade-off between thermogenesis and ATP synthesis (Balloux et al, 2009). This trade-off might explain differences in disease risk between different mtDNA haplogroups. Haplogroup U, in particular, is associated with a lower risk of glaucoma (Wolf et al., 2010). There also seems to be an age-related association between this haplogroup and risk of Alzheimer’s (Santoro et al., 2010).
If true, the decline of U-type haplogroups among early farmers may reflect the different patterns of physical activity between them and hunter/fisher/gatherers.
So was it cultural diffusion or population replacement?
The jury is still out, but the consensus is moving towards a position where Middle Easterners initially established pioneer farming settlements in central Europe but were over time largely replaced by native farmers. Rowley-Conwy (2011, p. S434) describes this new model:
Our explanations must now rest on two major foundations: most Neolithic genes were native, but the major domesticates were exotic. Small-scale rather than continent-wide migrations are the best way to integrate these into one model. Agriculture in a region may have been introduced by immigrants, but that does not mean that the immigrants carried mainly Near Eastern genes (Richards 2003; Rowley-Conwy 2004b; Zvelebil 2005). The LBK, for example, originated in the Carpathian Basin; the population that moved westward emerged there carrying a complex mix of European and Near Eastern mtDNA and no doubt picking up more as it moved.
There is evidence that these pioneer farming settlements assimilated local hunter-gatherers, especially women. In at least some cemeteries, the female skeletons are likelier than the male skeletons to have come from outside the local farming community (Rowley-Conwy, 2011, p. S439). Thus, over time, this recruitment of local hunter-gatherers would have steadily diluted the original gene pool, and this dilution would have been more advanced in later, secondary settlements that budded off from the early centers of colonization.
This process was hastened by the extinction of many of the early farming settlements. In northwestern France, the Villeneuve-Saint-Germain culture represented the furthest westward extension of these colonizing farmers. After a couple of centuries, however, it disappeared and was replaced by farming cultures of local origin (Rowley-Conwy, 2011, p. S439)
References
Balloux F., L.J. Handley, T. Jombart, H. Liu, and A. Manica (2009). Climate shaped the worldwide distribution of human mitochondrial DNA sequence variation. Proceedings. Biological Sciences, 276 (1672), 3447–55.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817182/?tool=pmcentrez
Cochran, G. (2011). First-mover advantage, West Hunter, November 25
http://westhunt.wordpress.com/2011/11/25/first-mover-advantage/#comments
Melchior, L., N. Lynnerup, H.R. Siegismund, T. Kivisild, J. Dissing. (2010). Genetic diversity among ancient Nordic populations, PLoS ONE, 5(7): e11898
Rowley-Conwy, P. (2011). Westward Ho! The Spread of Agriculturalism from Central Europe to the Atlantic, Current Anthropology, 52 (S4), S431-S451
Santoro A., V. Balbi, E. Balducci, C. Pirazzini, F. Rosini, et al. (2010). Evidence for Sub-Haplogroup H5 of Mitochondrial DNA as a Risk Factor for Late Onset Alzheimer's Disease. PLoS ONE, 5(8): e12037. doi:10.1371/journal.pone.0012037
Wolf, C., E. Gramer, B. Müller-Myhsok, F. Pasutto, B. Wissinger, & N. Weisschuh. (2010). Mitochondrial haplogroup U is associated with a reduced risk to develop exfoliation glaucoma in the German population, BMC Genetics, 11, 8
17 comments:
First two links
History lesson from the first farmers.
Cultivation of cereals by the first farmers was not more productive than foraging
John Hawks on Poor Ötzi's doomed mitochondria
"The Iceman is hardly singular: Remember that the mtDNA pool of Central Europe in the Neolithic was dominated by lineages that are now rare. And Medieval Danes had several mtDNA sequences that are now rare or absent in Scandinavia. And the Cambridge sequence has been increasing in frequency in Britain since medieval times. And so on.
Moreover why do north Europeans have delicate facial features?
Visualization of the shape regression on 2D : 4D ratio The least masculine 2D:4D has a face that, to me at least, looks north European.
Facial breadth seems to distinguish those faces.
I'm not sure that facial breadth is considered, by anyone, indicative of Northern European rather than South European or Middle Eastern types. Certainly, paleolithic Europeans, as opposed to neolithic Near Eastern populations, were characterised by broad faces and low orbits. This is the element that physical anthropology seems to say still distinguishes Northern Europeans from Southern Europeans.
Also, puzzlingly for this link, facial breadth, it's not really what distinguishes men and women within population. Men and women within population are largely distinguished by males having smaller and more rectangular orbits and eyes and larger jaws (everything from the nose down) and slightly wider cheekbones and noses relative to face size. The area between the eyebrows and mouth is relatively shorter and broader in the male than female, but not the face as a whole (considering the forehead and chin as well).
Wide Faces Predict Unethical Behavior Follow the aggression link "Men in general have wider faces than women do, a difference in the sexes that emerges at puberty as testosterone levels rise. At the same time, testosterone is tied with aggression, leading researchers to search for a link between aggression and wide faces."
Low 2D:4D goes with a suite of traits that facilitate reproduction under conditions of intense male-male competition. Second to fourth digit ratio: a predictor of adult penile length. Semen Displacement as a Sperm Competition Strategy in Humans
Sean,
Check the paper out - the figure showing the face morphs in question is on the second page http://carrelab.com/Carre_et_al_2009_Psyc_Sci.pdf.
You can see that like I stated, it is the face between brow and mouth that is shorter and thus wider in the "high ratio" group. In the words of the paper "Specifically, the distance between the left and right zygion (bizygomatic width) (i.e. cheekbones) was divided by the distance between the upper lip and mid-brow (upper facial height) to yield the facial WHR ". The high ratio faces are obviously not wider from top of forehead to bottom of chin. The masculine characteristic of narrow orbits and wide cheekbones is also in place in the high ratio group.
I don't think the faces they use are perfectly reflective of males and females though - females don't have massively wide noses compared to males, but if anything slightly the opposite. But it is still characteristic.
Peter,
I had a quick look around for more information relating to the Rowley-Conwy paper (very cursory like) and found this - http://secondaryrefuse.blogspot.com/2011/05/rowley-conwy-2011.html, which had a point interesting to me "(Rowley-Conwy's) argument that dairying was an important component of the Early Neolithic in Europe.".
To turn Greg's argument on its head, perhaps European foragers used to mobility would "be better at" habitually roving pastoralism "than the" sedentary farmer immigrants "could be". Immigrant farmers might be descended from people who could make the leap to colonise a new area, but eventually they regress to their mean of the sedentary personality profiles of their parent communities, and become poor pastoralists. Imagine a US history in which the "cow boys" had a much better productivity than the farm boys and where the Indians had naturally made much better cowboys than the pioneers. Imagine the technological gap between the "Indians" and pioneers was much lower. What would the story of the Wild West be there?
Otzy the Iceman was browned eyes with brown hairs, much like a Sardinian and definitely not like today's Swiss. Was he a traveller and what about his skin?
Also, researchers never mentioned he could have been killed because he had an intestinal worm parasite, which could appear to locals as an evil spirit.
The difference between men and women is another issue to the difference between low and high 2d:4d males.
Sean,
From an individual's standpoint, the shift to farming was a change for the worse. People had to work harder and their diet was less nutritious.
From a demographic standpoint, however, it was clearly a change for the better. Farming can support much larger populations, which can overwhelm hunter-gatherers.
A similar argument is sometimes made for the United States. If, as seems likely, the U.S. will grow to over half a million people by mid-century, the overall standard of living will be lower. But the U.S. will be militarily stronger.
There'll be lots of cannon fodder for military adventurism.
Matt,
Interesting explanation. Another reason might be soil exhaustion. The immigrant farming communities would have been the first to suffer, and their place might have been taken by later, more indigenous communities.
Ben10,
As I understand it, Switzerland was Celtic in population until the Germanic expansion of the 4th century onward. Perhaps brown eyes and brown hair were previously the norm.
It's hard to tell from a single individual. One swallow doesn't make a summer.
Another reason might be soil exhaustion.The immigrant farming communities would have been the first to suffer
Not something I'd considered That might be a more correct idea. Not necessarily unconnected though - mobility is also a way to deal with soil depletion (through swiddening in Europe's forests), as well as connected to pastoralism.
"Farming can support much larger populations, which can overwhelm hunter-gatherers."
All other things being equal, but the ME farmers are said to have drastically altered their appearance under selection pressure. Can't have it both ways. If there was a selection pressure related to vitamin D powerful enough to produce striking genetic change in the ME farmers then the early ME farmers must have had a very tough time of it, many failing to reproduce.
As I understand it Gregory Cochran and Henry Harpending are subscribing to the 'adoption of agriculture caused skin lightening in northern latitudes hypothesis." They're arguing that ME farmers' appearance transformed under strong selection to adapt to European conditions. The immigrants multiplied and swamped the Euro hunter gatherers.
But did the farmers' population take off in that way? By my way of thinking GC&HH's explaination contains a internal contradiction. It ignores that when those ME farmers first arrived they and their decendants were not adapted to thrive in Europe. If you accept what 10,000YE says about the dearth of ultraviolet flux for vitamin D synthesis in Europe, and meat being rich in vitamin D. It follows that an agricultural diet would have made those following it (ie the ME farmers) far less fit and reproductively competent than the native European hunter-gatherers.
Skin lightening takes time and the further north the went they the more lightening would be required. How many generations would it take for their skin to lighten again? And for all that time they would be handicapped by the putative severe pressure for adaption to inadequate vitamin D from UV-B while eating an agricultural diet with no vitamin D in it.
Mitochondrial nt3010G-nt3970C haplotype is implicated in high-altitude adaptation of Tibetans.
Sean:"...Skin lightening takes time and the further north the went they the more lightening would be required. How many generations would it take for their skin to lighten again?.."
Why?
Siberian researchers have breed foxes and obtained neotenic features in only three generations.
If sexual selection was at work in postglacial europe, it could have been that fast.
Unfortunatly, unless we know the timing of these events, we'll never know.
Ben 10, 3 generations ? Even if that's true you're missing an essential point: the foxes were bred from the tiny minority that showed some sign of the the desired characteristics. Most did not. The ME farmers in Europe would have experienced a catastrophic population crash under natural selection for extra vitamin D synthesis. And that's just due to the putative vitamin D deficiency. Cereal diets (which contain calcium blocking phylate) can cause rickets in the sunniest of countries Nutritional rickets around the world: causes and future directions "Rickets exists along a spectrum ranging from isolated vitamin D deficiency to isolated calcium deficiency. Along the spectrum, it is likely that relative deficiencies of calcium and vitamin D interact with genetic and/or environmental factors to stimulate the development of rickets. Vitamin D supplementation alone might not prevent or treat rickets in populations with limited calcium intake."
Pellagra in the US south was caused by a cereal diet cereal diet.
Nutritional rickets would have been a problem for farmers on a cereal diet. Which food is the best for counteracting nutritional rickets? Milk an excellent source of calcium and protein.
Which book explains the Kurgans managing to expand so fast because they drank a lot of milk. The 10,000 Year Explosion, page 180.
Rickets is a nutritional (or more rarely genetic) disease even in northern Europe
Pediatric Nephrology 2011 New thoughts concerning the epidemic of rickets: was the role of alum overlooked? .
BBC today "A rare genetic variant which causes reduced levels of vitamin D appears to be directly linked to multiple sclerosis. [...]
When people inherit two copies of this gene they develop a genetic form of rickets - a disease caused by vitamin D deficiency. Just one copy of the mutated CYP27B1 gene affects a key enzyme which leads people with it to have lower levels of vitamin D".
So that gene evolved to make us sick. Is the bad gene vanishingly rare ? No.
"The researchers then looked for the rare gene variant in over 3,000 families of unaffected parents with a child with MS. They found 35 parents who carried one copy of this variant along with one normal copy"
John Hawks has a post about the colour traits of archiacs."Lalueza-Fox and colleagues [1] investigated the MC1R gene in Neandertal [...] a similar effect to other mutations that contribute to red hair color, so at least some Neandertals were likely to have had this pigmentation."
The 10,000 Year Explosion "Vitamin D was not abundant in the new cereal-based diet, and any resulting shortages would have been serious, since they could lead to bone malformations (rickets), decreased resistance to infectious diseases, and even cancer. ..."
Neanderthals were meat eaters so a switch to agriculture couldn't be the explanation for light pigmented Neanderthals. Could it be that the appearance of light pigmentation is what made it valuable for Neanderthals? Ambush predators would benefit from pigmentation that made them blend into the reddish reflected light in the forest. Like the book ' Why are Orangutans Orange?' says: it makes them difficult to see.
You're wrong. Hint: don't listen to Rowley-Conwy. He's leaning on Soares, who thinks that the fact that most major European mtDNA
lineages diverge before the Neolithic proves that they are indigenous.
Not so.
Strange. Shown to be right that mtDNA proved nothing (about Neanderthal ancestry in modern humans). Now espousing an argument that European hunter gatherers died out based on mtDNA data.
Denmark has the lowest 2D:4D in the world. "In Denmark one in 8 children is born to couples where medical assistance is needed due to low male sperm count".
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If being a hunter gatherer provided the required calcium and vitamin D one would expect African hunter gatherer populations (ie the Khoisan and Oromo of Ethiopia (genetically alike, and I believe with mtDNA basal to everybody else) to have skin darker than those African populations who have cultivated cereal grains for thousands of years. They don't.
Bantu expansion
"Judging from all those U5 mtdna results from ancient skeletons"
Maybe we should wait for ancient DNA from the south half of europe (i.e. the most populated half) before jumping to conclusions, Especially because some mesolithic Iberian results seem more conform to modern mtDNA pool:
(3rd map frome the top)
http://forwhattheywereweare.blogspot.com/p/ancient-mtdna-maps-of-europe.html
The fact that the 12,000 yrs old Taforalt (north-east Morocco) ancient DNA of Cro-magnoids (Kefi et al, 2005) that seems to be linked to a migration from Europe (Ibero-maurusian culture) had apparently a lot of mtDNA that would fit modern European mtDNA could also be a sign.
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