First Europeans could not digest milk

Study provides new insights on the evolution of man

Decontamination of skeletons under UV irradiation. © Joachim Burger
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The ability of adults to digest lactose and thus milk has played a major role in the evolution of Europeans. This has now been demonstrated by an international team of scientists studying several thousand years old Neolithic skeletons. The researchers discovered that the so-called lactase persistence in Europe in the early Neolithic period was barely existent and apparently evolved only in the last 8, 000 years.

"The ability of us adults to digest milk without problems, therefore, must later have spread through natural selection, " says Professor Joachim Burger from the Institute of Anthropology, University of Mainz. "Probably, the ability to digest milk has even brought a decisive selection advantage in the development of sedentary farmers and ranchers in central and northern Europe." The researchers from Mainz, together with colleagues from University College London, report in the journal Proceedings of the National Academy of Sciences (PNAS) about their investigations, which were based on old genetic material - so-called aDNA - from archaeological skeletons.

Northern Europeans and Africans can digest milk

Lactase is the enzyme that helps digest the lactose in the human body. In infancy, it is present in sufficient quantities in humans, but is produced after weaning only to a much lesser extent, so that milk in adulthood is very poor physiological use. It's the same all over the world, except in Europe and parts of Africa. In particular, the inhabitants of northern Europe produce the enzyme lactase beyond the baby's age, which is why they can easily process milk in large quantities as adults. The same is true of a few populations of Africa, where this characteristic, called lactase persistence, has probably developed independently of the Europeans.

About 70 percent of people in Northern Germany, Scandinavia or the Netherlands have lactase persistence. The frequency decreases to the south, so that it is approximately completely absent in southern Italy. The paleo-geneticists from Mainz have now shown that this distribution has emerged only in the last 8, 000 years, as a result of natural selection. Together with an English colleague, they studied skeletons from the Meso and Neolithic periods using molecular genetic methods - that is, from the time when hunter-gatherers turned people into farmers and ranchers. The anthropologists noted that the characteristic of lactase persistence at that time was still almost absent in Europe.

Evolution re success story

The high frequency of the present, especially in northern Europe, must have arisen as a result of natural selection in the period after the early Neolithic. When the first domesticated goats, sheep and cattle were introduced to Europe around 8, 000 years ago, the majority of early farmers were unable to digest their milk. The small minority, which was already able to do so, experienced an evolutionary success story from then on. Due to its small physiological-genetic variant, this minority was so favored by evolution for millennia that the frequency of the characteristic increased from almost zero to more than 70 percent. display

In order to protect the samples from contamination, protective clothing must be worn in the aDNA trace laboratory. AG Palaeogenetics

"Milk is a high-energy drink that is also rich in calcium, " explains Martina Kirchner, who has studied prehistoric lactase persistence in the trace laboratory for ancient DNA in Mainz. "With milk, the high rate of child mortality after weaning could be reduced and, in addition, years with bad harvests could be energetically substituted, " adds anthropologist Joachim Burger, head of the working group Palaeogenetics in Mainz.

First direct evidence of positive selection in humans

To be able to utilize lactose physiologically must have had such a high evolutionary advantage in prehistory that in this context the researchers speak of the gene with the possibly highest positive selection in the entire human genome,

"This is the first direct demonstration of positive selection in humans, " stresses the population geneticist Mark G. Thomas of University College, London, co-author of the study. And indeed, selection must have taken place to a very high degree, because for the propagation of a trait, 8, 000 years in evolutionary time are very few. Culturally-social factors may have further fueled biological evolution. It is conceivable that those Neolithic livestock farmers who were lactase-persistent could, thanks to their precious milk and meat resource, not only feed more children, but at the same time develop more prestige and power, thus increasing prosperity and high progeny numbers from generation to generation becoming more and more firmly established among livestock and dairy farmers.

Just over a year ago, Burgers team already showed that the early Neolithic peasants were not the ancestors of today's Europeans. Now it seems likely that today's Northern and Central Europeans can call a small group of milk-drinking cattle farmers of the fifth millennium BC their ancestors.

(idw - University Mainz, 27.02.2007 - DLO)