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Spread of farming in Europe. Der Spiegel

New research has revealed that agriculture came to Europe amid a wave of immigration from the Middle East during the Neolithic period. The newcomers won out over the locals because of their sophisticated culture, mastery of agriculture — and their miracle food, milk.
(Schulz 2010)

This recent Der Spiegel article has stirred up comment in the blogosphere (Hawks 2010, Khan 2010, Sailer 2010). It argues that Europeans do not descend from the reindeer hunters who once roamed the continent during the last ice age. Nor do they descend from the more recent hunter-fisher-gatherers of the Mesolithic. All of those people went extinct. They were replaced by the real ancestors of present-day Europeans—farmers who began to spread out of the Middle East only 9,000 years ago and who reached northern Europe two millennia later—almost at the dawn of history!

If you have any doubts, this finding is based on “a barrage of articles in professional journals like Nature and BMC Evolutionary Biology, [whose authors] have turned many of the prevailing views upside down over the course of the last three years.”

There is nothing wrong with the above journal articles. A lot is wrong, however, with the Der Spiegel article. It neatly confuses two separate findings, only one of which supports the ‘population replacement’ hypothesis.

1. Origins of the European allele for adult digestion of lactose

Unlike most humans, Europeans can digest milk sugar (lactose) as adults. This is made possible by an allele that allows adults to produce an enzyme, lactase, that breaks down milk sugar. So where did this allele come from? Did it originate in Europe or in some place outside Europe?

According to Der Spiegel:

But where did the first milk drinker live? Which early man was the first to feast on cow’s milk without suffering the consequences?

In a bid to solve the mystery, molecular biologists have sawed into and analyzed countless Neolithic bones. The breakthrough came last year, when scientists discovered that the first milk drinkers lived in the territory of present-day Austria,
Hungary and Slovakia.

The reader is left with the impression that the new allele had been brought to Europe from the Middle East. That impression is false. In fact, the above molecular biologists found no trace of this allele in DNA retrieved from the earliest European farmers. It apparently arose later as a mutation and then spread among Europeans through natural selection.

[…] the absence of the 13.910*T allele in our Neolithic samples indicates that the early farmers in Europe were not yet adapted to the consumption of unprocessed milk. Dairying is unlikely to have spread uniformly over Europe, and the use of milk in the Early Neolithic may have been rare. Although our data are consistent with strong selection for LP [lactose persistence] beginning with the introduction of cattle to Europe ?8800 B.P., it is unlikely that fresh milk consumption was widespread in Europe before frequencies of the 13.910*T allele had risen appreciably during the millennia after the onset of farming.
(Burger et al. 2007)

Consequently, this area of research argues against the Der Spiegel article. Europeans did change genetically, but the change occurred through natural selection, not through population replacement (1).

2. Genetic divide between late hunter-fisher-gatherers and early farmers

Researchers have also retrieved mitochondrial DNA from Europe’s late hunter-fisher-gatherers and early farmers. Comparison shows a sharp genetic divide between the two groups. In particular, the first group had high incidences of haplogroup U—a genetic lineage that was rare among early farmers and still is among present-day Europeans.

The past year, however, has brought evidence of genetic continuity. After studying 92 Danish human remains that range in time from the Mesolithic to the Middle Ages, Melchior et al. (2010) found that high incidences of haplogroup U persisted among the earliest farmers and declined only in later groups.

Thus, the sharp genetic divide was not between late hunter-fisher-gatherers and early farmers. It seems to have been between the earliest farmers and groups that had been farming for at least a millennium or so. Once again, the evidence points to natural selection, and not to population replacement.

But isn’t mtDNA unresponsive to natural selection? That’s what I and others used to think. There is growing evidence, however, that some mtDNA loci can change in response to natural selection. In particular, some haplogroups seem to reflect a tradeoff between thermogenesis and ATP synthesis (Balloux et al 2009). If true, the decline of U-type haplogroups among early farmers may reflect the differences in physical activity (leading to overheating or underheating) that exist between hunting/fishing/gathering and farming.

Conclusion

The jury is still out. The evidence, however, seems to be tilting toward natural selection and away from population replacement as the best way to explain these genetic changes among ancestral Europeans. In short, the Der Spiegel article is bad science.

And bad journalism.

Note

1. Towards the end, the Der Spiegel article seems to acknowledge that the allele for adult digestion of lactose must have arisen after farming had spread to Europe:

Some [farmers] had genetic mutations that enabled them to drink milk without getting sick. They were the true progenitors of the movement.

As a result of “accelerated evolution,” says Burger, lactose tolerance was selected for on a large scale within the population in the space of about 100 generations. Europe became the land of the eternal infant as people began drinking milk their whole lives

(Schulz 2010)

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

Burger, J., M. Kirchner, B. Bramanti, W. Haak, and M.G. Thomas. (2007). Absence of the lactase-persistence-associated allele in early Neolithic Europeans, Proceedings of the National Academy of Science, 104(10), 3736-3741.
http://www.pnas.org/content/104/10/3736.full

Hawks, J. (2010). Neolithic milk fog, John Hawks weblog, October 17.
http://johnhawks.net/weblog/topics/demography/neolithic/spiegel-volkerwanderung-2010.html

Khan, R. (2010). Völkerwanderung back with a vengeance, Discover, October 17.
http://blogs.discovermagazine.com/gnxp/2010/10/volkerwanderung-back-with-a-vengeance/
Melchior, L., N. Lynnerup, H.R. Siegismund, T. Kivisild, J. Dissing. (2010). Genetic diversity among ancient Nordic populations, PLoS ONE, 5(7), e11898.
doi:10.1371/journal.pone.0011898

Sailer, S. (2010). Are Europeans all Middle Easterners? October 17.
http://isteve.blogspot.com/2010/10/are-europeans-all-middle-easterners.html

Schulz, M. (2010). How Middle Eastern Milk Drinkers Conquered Europe, Spiegel Online International, October 15.
http://www.spiegel.de/international/zeitgeist/0,1518,723310,00.html

(Republished from Evo and Proud by permission of author or representative)
 
• Category: Science • Tags: Europeans, Farmers, Genetics, Lactose, MTDNA 
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  1. Ben10 says:

    Lactose tolerance fo milk might also help to digest processed milk, like cheese.
    Milk is nice to have but you need a cow at disposition since you can only drink it fresh and you can't transport it.
    Yogourt is fermented and asians horse riders were famous to make it, but i don't think it is easily transportable either.
    But if you are a hunter, cheese is by far the best way to keep and transport milk. I have been hiking in Corsica in summer (35-40degreC) and carried local cheese in the backpack for days. It was very good despite the absence of refrigerators and anyway the cheese was hard like a rock when kept in a refrigerator.
    By contrast, my father and my daughter abhore cheese. They show some sort of intinctive disgust at the sight of cheese. I did not teach that to my daughter since I am a heavy cheese eater (but no milk drinker, thanks to beer). My father told me once that for him, cheese taste like 'shit', litteraly. So I would not be surprised if the allele to digest lactose also helped to digest cheese or not feeling repulsed by it.

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  2. Anonymous • Disclaimer says:

    Ben 10 said


    My father told me once that for him, cheese taste like 'shit', litteraly. So I would not be surprised if the allele to digest lactose also helped to digest cheese or not feeling repulsed by it.

    Cantonese speakers refer to cheese as pig shit because of the smell and that fact that the pronunciation of pig shit in Cantonese is close in sound to the pronunciation of cheese.

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  3. Anonymous • Disclaimer says:

    I would imagine that cow's and goat's milk was first fed to children and had a dual impact on mothers:

    1. They did not have to produce so much milk for such a long time

    2. They could have more babies.

    It would also have improved childhood nutrition …

    I have seen Asian kids who breast-fed until about age 5. Being able to feed kids milk from animals would help them be much more robust …

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  4. Ben10 says:

    But I thought lactose tolerance was important for adultd only since kids digest milk anyway.
    Do you need lactose tolerance to digest cow milk even as a baby ?

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  5. Anonymous • Disclaimer says:

    Ben10 asked:


    But I thought lactose tolerance was important for adultd only since kids digest milk anyway.
    Do you need lactose tolerance to digest cow milk even as a baby ?

    Of course kids have lactose tolerance. Among those populations that do not have extended lactose tolerance, adults no longer have the ability to create large amounts of lactase.

    If you can improve the nutrition of your children through using animals that can turn grass into meat and milk then you improve the health of mothers and children.

    That produces a big boost to reproductive success!

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  6. Tod says:

    " the decline of U-type haplogroups among early farmers may reflect the differences in physical activity (leading to overheating or underheating) that exist between hunting/fishing/gathering and farming."

    When wearing clothes in extreme cold it can be disadvantageous to sweat as the sweat cools down or even freezes.

    Are hunter gathers really more or less selected to not overheat? An agricultural diet with vastly more glucose to be metabolized is still a possible explaination for why selection for different mtDNA ocurred in agriculturists.

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  7. Ben10 and Anon,

    I suspect that many differences among human populations exist because some populations have retained into adulthood certain traits that were formerly expressed only in infancy.

    This is a case where evolution can proceed rapidly, since the actual mechanism is already in place.

    Tod,

    You may be right. I focused on the overheating hypothesis because we now have evidence that links some mtDNA loci to body temperature.

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  8. Anonymous • Disclaimer says:

    Peter Frost said:


    I suspect that many differences among human populations exist because some populations have retained into adulthood certain traits that were formerly expressed only in infancy.

    Sure, but I suspect that the path to adult retention of lactase production is more likely to have occurred through the use of animal milk first to feed infants.

    Once you are using animals to produce milk you would then see selection for those individuals who can make use of it for an extended period of time, however, it seems to me that the initial big win is getting more nutrition into infants (and allowing them to survive) and freeing mothers to produce more babies.

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  9. Anonymous • Disclaimer says:

    It is interesting that the Mongols seem to have a high incidence of lactose tolerance but the Chinese not.

    I suspect that the introgression of the lactase persistence genes into the Chinese comes from Mongol males during the Yuan dynasty.

    Further, it seems that Mongols had little opportunity to provide the necessary nutrition in other ways, so the lactase persistence one happened for them. Since they move all the time, mare's milk was the way.

    However, among the Chinese, rice cultivation means that they can provide rice gruel to their children, which while not protein/fat rich unless these are added, provide plenty of carbs.

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  10. Anonymous • Disclaimer says: • Website

    They show some sort of intinctive disgust at the sight of cheese. I did not teach that to my daughter since I am a heavy cheese eater

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