Early man 'couldn't stomach milk' (bbc news)
In order to digest milk, adult humans need to have a gene which produces an enzyme called lactase to break down lactose, one of the main sugars it contains.
Without it, a drink of milk proves an uncomfortable experience, causing bloating, stomach cramps and diarrhoea.
Today, more than 90% of people of northern European origin have the gene.
Working with scientists from Mainz University in Germany, the UCL team looked for the gene that produces the lactase enzyme in Neolithic skeletons dating between 5480BC and 5000BC.
These are believed to be from some of the earliest farming communities in Europe.
The lactase gene was absent from the DNA extracted from these skeletons, suggesting that these early Europeans would not be tolerant to milk.
Dr Mark Thomas, from UCL, 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, they probably include the advantage of a continuous supply compared with the 'boom and bust' of seasonal crops, its nourishing qualities, and the fact that, unlike stream water, it's uncontaminated with parasites, making it safer.
"All in all, the ability to drink milk gave some early Europeans a big survival advantage."