milk had a key nutritional role and the ability to drink it conferred an enormous advantage, a few thousand years ago ?

An extract of. the article related to milk in http://www.bbc.co.uk/news/science-environment-24475342

Quote: "Dr Wells thinks this precarious existence may be reflected in the spread of the lactase persistence gene, which enables people to digest milk into adulthood. Scandinavian populations have some of the highest frequencies of this gene variant in Europe, and it appears to have undergone strong natural selection in the last few thousand years - suggesting milk had a key nutritional role and the ability to drink it conferred an enormous advantage." Unquote. 

My own Note for reference: CUemailY. Hg.

Source of image below:

http://www.68degrees.com.hk/blog/?p=419