MILK

while some people drink it every day and with pleasure, most adults in the world are lactose intolerant and can’t digest the stuff. So, why is a small group capable of metabolizing dairy?

Well, to digest milk humans need an enzyme called lactase, which is coded into the LCT gene common to all humans. However, for most people, this gene goes inactive after infancy – that is, except for those of European descent.

The ability to digest milk emerged in Europe between the years 5,000 and 10,000 BCE as a result of a single letter change in the LCT gene. This change was brought about by the emergence of dairy farming among Europeans.

More specifically, genetic analysis can pinpoint its emergence somewhere around what’s now Slovakia, Poland or Hungary. Meanwhile, groups in Africa and Asia developed the ability to digest lactose thanks to different mutations. Simply put, lactase persistence likely proved advantageous and was therefore selected for during human evolution.

And it’s not just culture. Since genes change due to environmental factors, genetic analysis also allows us to study human migration.

People of European descent offer another good example because of one more stand-out characteristic: their skin color. After all, the humans who migrated from Africa to Europe 50,000 years ago were dark-skinned, which makes sense since dark skin is an adaptation to sunny weather. Yet the people who live there now are not.

How come?

Well, bone analysis tells us that 7,700 years ago, the humans living in what’s now Sweden had genes that acted together to produce light skin, as well as blonde hair and blue eyes.