Cow's milk was indigestible to all our neolithic ancestors

By Ernest Gill Mar 12, 2007, 16:30 GMT

Hamburg - As recently as 7,000 years ago, our neolithic ancestors were unable to digest cow's milk and became ill if they tried to drink it, according to new research.

Today billions of people in Africa and Asia still lack the gene necessary to produce enzymes that allow humans to digest milk from the bovine species. Nearly all Europeans and Americans, however, can drink milk - and often do so daily.

But Europeans only learned to stomach milk within the last 7,000 years, the new research suggests.

Human remains dating to 5,000 BC were found to be missing the gene that allows adults to digest milk without unpleasant side effects.

Milk tolerance must have evolved rapidly alongside the emergence of dairy farming, providing early Europeans with a major survival advantage, said scientists.

Today, more than 90 per cent of northern Europeans can drink milk without ill effects, as can some African and Middle Eastern populations.

However, most of the rest of the adult global population are still unable to digest the natural milk sugar lactose.

While infants have no problem coping with lactose, this is not the case for all adults. Lactose tolerance depends on the enzyme lactase, which enables the sugar to be broken down in the body. Without it, drinking milk or consuming dairy products results in bloating and diarrhoea.

Dr Mark Thomas, part of an Anglo-German team which came up with the findings, said: 'The ability to drink milk is the most advantageous trait that's evolved in Europeans in the recent past.

'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.'

Thomas, from University College London, was part of the team that carried out DNA tests on Neolithic skeletons from some of the earliest farming communities in Europe, dating to between 5,000 and 5,840 BC.

The aim was to see whether the early farmers carried a version of the lactase gene that allows an adult to digest lactose.

The scientists found that the gene was missing from the ancient bone DNA. Milk tolerance would therefore have been very rare or absent at the time the farmers were alive.

'To go from lactose tolerance being rare or absent seven to 8,000 years ago to the commonality we see today in central and northern Europeans just cannot be explained by anything except strong natural selection,' said Thomas.

'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.'

The findings were published in the journal Proceedings of the National Academy of Sciences.

They challenge the theory that certain groups of Europeans were innately lactose tolerant and that this inborn ability led them to pursue dairy farming.

Instead, it now seems more likely that they evolved their tolerance through exposure to milk.

Thomas added: '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 9,000 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 80 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.'