The finding that Cheddar Man was lactose intolerant — that he carried the ancestral form of the LCT gene that causes lactase production to decline after childhood — is worth examining in more detail because it illuminates one of the most powerful examples of recent natural selection in human evolution.

The gene that controls lactase production — the LCT gene — has a specific variant, located in a regulatory region upstream of the gene rather than in the gene itself, that allows continued lactase expression throughout adult life.

This variant, called LP for lactase persistence, is found at high frequencies in populations of northern European descent and in certain African and Middle Eastern populations where cattle herding has a long history.

In Mesolithic Europe, before the arrival of farming and the domestication of cattle, there was no selective pressure favoring LP.