Europeans from around 5000 BC could not handle milk products. However, lactose tolerance improved quickly, so that nowadays it is present in +90% of north-Europeans.
DNA analisys of Neolithic skeletons found that they did not posess the lactase gene that produces the lactase enzyme.
Lactose intolerance is the condition in which lactase, an enzyme needed for proper metabolization of lactose (a sugar that is a constituent of milk and other dairy products), is not produced in adulthood. A lactose tolerance test, a hydrogen breath test, or a stool acidity test is required for a clinical diagnosis.
Lactose intolerance can sometimes be confused with milk allergy, the former is a lack of the enzyme lactase, the latter is an autoimmune reaction (usually) to milk proteins.
With lactose intolerance, the result of consuming too much lactose is excess gas production, stomach aches and often diarrhea. Most lactose-intolerant adults can drink about 250 ml (8 oz) of milk per day without severe symptoms.
Dr Mark Thomas, UCL Biology: "The ability to drink milk is the most advantageous trait that's evolved in Europeans in the recent past. Without the enzyme lactase, drinking milk in adulthood causes bloating and diarrhoea. Although the benefits of milk tolerance are not fully understood yet, they probably include: the continuous supply of milk compared to the boom and bust of seasonal crops; its nourishing qualities; and the fact that it's uncontaminated by parasites, unlike stream water, making it a safer drink. All in all, the ability to drink milk gave some early Europeans a big survival advantage.
To go from lactose tolerance being rare or absent seven to eight thousand years ago to the commonality we see today in central and northern Europeans just cannot be explained by anything except strong natural selection. Our study confirms that the variant of the lactase gene appeared very recently in evolutionary terms and that it became common because it gave its carriers a massive survival advantage. Scientists have inferred this already through analysis of genes in today's population but we've confirmed it by going back and looking at ancient DNA.
There were two theories out there: one that lactose tolerance led to dairy farming and another that exposure to milk led to the evolution of lactose tolerance. This is a simple chicken or egg question but one that is very important to archaeologists, anthropologists and evolutionary biologists. We found that the lactose tolerance variant of the lactase gene only became common after dairy farming, which started around 9 thousand years ago in Europe.
This is just one part of the picture researchers are gathering about lactose tolerance and the origins of Europeans. Next on the list is why there is such disparity in lactose tolerance between populations. It's striking, for example, that today around eighty per cent of southern Europeans cannot tolerate lactose even though the first dairy farmers in Europe probably lived in those areas. Through computer simulations and DNA testing we are beginning to get glimpses of the bigger early European picture."
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