Saturday, May 5, 2012

Who were the ancestors of modern Europeans?

A mitochondrion (source). Is mitochondrial DNA selectively neutral?

Were Ice Age Europeans a dead end, like the Neanderthals before them? Did Middle Eastern farmers replace indigenous hunter-gatherers, just as Europeans would later replace native Indians in North America?

This debate has been raging back and forth for some time, but it has now entered a new phase with retrieval of mtDNA from ancient European skeletons. We can now genetically compare late hunter-gatherers with early farmers. We can now ask the question: Which of them were the ancestors of modern Europeans?

This kind of comparison has recently been made in Sweden, where farming replaced hunting/gathering/fishing some 5,000 years ago. This is the time depth for mtDNA retrieved from two burial sites: a farming community in Gökhem parish (one individual) and a hunter-gatherer community on the island of Gotland (three individuals). The results?

The Neolithic hunter-gatherers shared most alleles with northern Europeans, and the lowest allele sharing was with populations from southeastern Europe. In contrast, the Neolithic farmer shared the greatest fraction of alleles with southeastern European populations (Cypriots and Greeks) and showed a pattern of decreasing genetic similarity to populations from the northwest and northeast extremes of Europe (Skoglund etal., 2012)

The authors then went on to estimate the degree of admixture from Middle Eastern farmers in present-day Europeans:

We estimated that people of southern, central and northern Swedish descent are, on average, of 41 ± 8%, 36 ± 7%, and 31 ± 6% Neolithic farmer–related ancestry, respectively (±1 SE). Across Europe, this fraction decreases from 95 ± 13% in Sardinians to 52 ± 8% in the CEU population (individuals of northwestern European descent) and 11 ± 4% in Russians (Skoglund et al., 2012)

So, according to this study, northern Europeans are mainly descended from the hunter-gatherers of Ice Age Europe. But there is also substantial admixture from those Middle Eastern farmers—roughly a third of the present-day Swedish gene pool.

Is this the last word? No, the debate will surely continue. For one thing, the sample sizes are still small. For another, the replacement of hunter-gatherers by farmers may have played out differently in different places.

But there is a more fundamental objection. All of this assumes that we have a reliable yardstick for measuring admixture. For this to be so, mtDNA must not be influenced by natural selection. In particular, it must not be influenced by the change in selection pressures that occurs when hunting and gathering give way to farming. Is this assumption valid?

When we compare late hunter-gatherers with present-day Europeans, the main change to mtDNA is the loss of haplogroup U. Indeed, if this haplogroup had not declined to its current low levels, the above admixture estimates would be minimal.

Today, haplogroup U reaches high levels only among the Saami of Finland and the Mansi of northwestern Siberia, both of whom were hunter-gatherers until recently (Derbeneva et al, 2002). Did something about that lifestyle favor this haplogroup?

Balloux et al. (2009) have argued that some haplogroups create different trade-offs between thermogenesis and ATP synthesis. In particular, haplogroup U is associated with reduced sperm motility—an indication that the energy balance is shifted from producing ATP to producing heat:

The ATP that drives the sperm flagella is derived from the mitochondria located in the midpiece. Therefore, mutations in the mtDNA which increase or decrease ATP production will be reflected in increased or decreased sperm motility.

[…] Therefore, shifting the energy balance from primarily ATP production to increased heat production could explain the lower sperm motility and the predilection of these sublineages U to reside in colder climates and their northern distribution. (Montiel-Sosa et al., 2006)

Being nomadic, hunter-gatherers spent more time in the cold, especially when sleeping in temporary shelters. Farming brought more sedentary living and a generally warmer sleeping environment. There would thus have been weaker natural selection for genetic variants, like haplogroup U, that maintain a higher body temperature at the expense of lower ATP production.

This hypothesis is testable. If haplogroup U disappeared because Middle Eastern farmers partially replaced native hunter-gatherers, this genetic change should largely coincide with the time boundary between late hunter-gatherers and early farmers. If this haplogroup disappeared through natural selection, the change should have occurred gradually over a longer period.

The second scenario seems closer to the truth. In a study of 92 Danish human remains that ranged in time from the Mesolithic to the Middle Ages, Melchior et al. (2010) found that high incidences of haplogroup U persisted long after the advent of farming and apparently as late as the Early Iron Age.


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.

Derbeneva, O.A., E.B. Starikovskaya, D.C. Wallace, & R.I. Sukernik. (2002). Traces of early Eurasians in the Mansi of Northwest Siberia revealed by mitochondrial DNA analysis, Am. J. Hum. Genet. 70:1009–1014.

Melchior, L., N. Lynnerup, H.R. Siegismund, T. Kivisild, J. Dissing. (2010). Genetic diversity among ancient Nordic populations, PLoS ONE, 5(7): e11898

Montiel-Sosa, F., E. Ruiz-Pesini, J.A. Enríquez, A. Marcuello, C. Díez-Sánchez, J. Montoya, D.C. Wallace, & M.J. López-Pérez. (2006). Differences of sperm motility in mitochondrial DNA haplogroup U sublineages, Gene, 368, 21–27.

Skoglund, P., H. Malmström, M. Raghavan, J. Storå, P. Hall,  E. Willerslev, M.T. Gilbert, A. Götherström, & M. Jakobsson. (2012). Origins and genetic legacy of Neolithic farmers and hunter-gatherers in Europe, Science, 336, 466-469.


Sean said...

Russians, who you would think would be used to the cold, froze to death in tens of thousands when they invaded Finland in 1939. Adaptation to cold explains a lot. However, those peoples with
haplotype U also have had a different diet until very recently. I think a switch to an agricultural diet may have been a factor in, slowly but surely, selecting against haplotype U .

"Before the 20th century, the traditional Sami diet was composed almost exclusively of foods of animal origin (mainly reindeer) with the addition of fish and plant foods (eg, berries) when available" Here "mtDNA haplogroup U is associated with maternal family history of diabetes mellitus" Here

Pigmentation aside, how anyone could believe that North Europeans were Middle Easterners 7000 years ago is beyond me. The selection pressure for ME farmers' descendants to have acquired the European craniofacial form was supposed to be what exactly?

Kiwiguy said...

Peter, Razib Khan has a post up which addresses the catch phrase 'we are all africans' that you've raised previously.

As Razib notes it has attracted some commment on

Nanonymous said...

It would be really strange if all of the mt genome were completely neutral. mtDNA-encoded genes all code for protein in respiratory chain. mtDNA carries determinants involved in defining number of mitochondria per cell. Why would something that's central to number and efficiency of energy-producing organelles be neutral? I'd say no way. I haven't looked carefully but believe that there is a fair amount of work done on mitochondrial genetics and that almost all mutations analyzed in model organisms turn out to be deleterious.

Sean said...

The colonisation of Europe and our Western diseases."" It can be shown that the spread of agriculture from the Near East to the West and North of Europe with the accompanying differences in time for the adaptation to the new food (the carbohydrates) easily explains the geographic differences in the frequency of civilisatory diseases which is highest where (in Northern Ireland, Scotland and Finland) carbohydrates came last. Highest, too, in those areas is the 'polymorphism' of genes which are related to cardiovascular diseases" If almost all the genes in Ireland and Scotland came from ME farmers, as we are told mtDNA and Y-chromosome data suggest, why do those areas have such high rates of the diseases of civilization compared to the south of Europe.

Obviously there has been selection of mtDNA and the Y-chromosome for increased resistance to disease.

Y-chromosomal haplogroup I (hg-I) (more common in North and West British Isles) is associated with enhanced AIDS progression. Moreover the risk of coronary artery disease among men carrying Y-chromosome haplogroup I is 50% higher than in other men.

Ben10 said...

One can't say modern european were all farmers or that being 'modern' implies an agricultural lifestyle.

At the time of Cesar, the Gallic celts were practicing very advances farming. I've read that they developed a sort of automatic harvesting machine, which is consistent with a heavily populated Gaul. So OK, these were farmers.
But the germans were only relying on cattle and were more nomadic in life style. Roman historians report they were unable to sustain long hardship tasks in the summer heat, such as harvesting. To me, they were not really 'farmers'. They switched to an agricultural diet and sedentary lifestyle well after the gauls.

Sean said...

The Celtic areas of Britain have poor health Scotland worst in UK for early death

Relying on cattle can mean dairy farming and genes for digesting milk are commonest in north Europeans. The reliance on milk in Northern Europe might well have resulted in a much slower adaptation to cereal grains, thereby contibuting to worse health in Northern Europe.

Peter Frost said...


This is one of my big problems with the population replacement theory. All of the physical characteristics of northern Europeans would have therefore arisen over a very short time, basically three or four thousand years at most.

This kind of rapid evolution is possible only if one assumes very strong selection pressures, and such pressures would have to be all the stronger because we're dealing with farming peoples that have a much larger population base.


I saw that article by Razib. The catch-phrase "We are all Africans" assumes that no real evolution has occurred over the past 40 to 50 thousand years. Actually, evolution has occurred, and at a much faster rate than previously.


Yes, hunting and gathering co-existed with farming long after the advent of farming in Europe. To me, that fact suggests cultural change, rather than population replacement.

Sean said...

Peter, if you are saying it is virtually impossible that "All of the physical characteristics of northern Europeans [have] arisen over a very short time, basically three or four thousand years at most", then I have to disagree. Given a large enough 'effective population size' with agriculture it most certainly is possible mutations could spread that rapidly. But, the replacement-mongers have never explained what this selection pressure was. And they have never properly reflected on the agricultural nature of the putative selection pressure. Just living on agriculture in northern Europe is supposed to have resulted in ME farmers radically altering in appearance while differentiating into this and this.

It's never spelled out, but they are actually advancing sweeps of neutral or slightly deleterious mutants through the population. IE drift is their explaination. How explain the aforementioned differentiation in N. Europeans, given the effective population size of the agriculturists. Can't have it both ways.

Peter Frost said...


I agree. Perhaps I expressed myself poorly. A population can certainly undergo significant genetic change in as little as eight generations. But you're not going to get that rate of change with genetic drift or even weak-to-medium selection pressures.

When I talk with other academics about European physical features, especially hair and eye color, I get the impression that they've never really thought through their beliefs on this point. In fact, I'm not even sure whether the word "belief" is appropriate here.

On the one hand, they consider these physical features to be insignificant, so the evolutionary cause must be equally insignificant. On the other hand, however, they would like to believe that Europeans are of relatively recent origin, i.e., "We're all immigrants."

These two beliefs are incompatible. But, then, they're not really beliefs. They're more like statements about present reality than about past reality.

Sean said...

I dare say Razib Khan's writing about race attracts attention because his ethnic identity may be thought likely to function as an ideological-political pass to express what Dawkinsites see as axiomatic.

Peter, You explained yourself well, I'm afraid I was posturing.

Those asserting replacement(s) of hunter gatherer North Europeans by Middle Eastern farmers (who may in turn have been replaced by Indo-Europeans) seem to think that they have thought it through. They may have convincing models for waves of replacement, but these are extrapolations based on mathematical models which are necessarily simplified.

The original Anglo Saxon invaders of Britain were from a northern coast of Continental Europe where gravel soils made agriculture difficult. Abundant marine food meant hunter gatherers survived on a belt along this coast for a thousand years after farming reached them. The AS burials in Britain reveal skulls as thick as Cromagons' and massively build, in considerable contrast to the Celts. The Irish and Danes are supposed to have diverged from a single population which arrived in a wave of replacement ?

Long established farming populations have adaptations (hangovers) to prevent them over indulging in alcohol. The Irish, Scots and Swedes are all prone to heavy drinking. The northern European populations look significantly different. So how did all this diversity come about since all N. Europeans are supposed to have come from one and the same same population, and quite recently?

Anonymous said...

Living in Russia I was astonished seing British look like Mediterranian,dark-skinned Italians ans Spaniards as the mideast people,Swedes like the Russians often have broad faces and mongoloid eyes often."Non Aryan" finns with the same eyes are more blond than Svedes and so on...Europeans` appearence are not so European from the other side.Don`t worry,be happy.