How did humans evolve lactose tolerance?

CC-1923
A cow with an electronic milking machine attached to its udder. Needless to say, dairying was a lot less complicated in ancient times. Source: Wikimedia Commons, CC-1923

This article was originally published on NPR’s The Salt, 28 December 2012.

Got milk? Ancient European farmers who made cheese thousands of years ago certainly had it. But at that time, they lacked a genetic mutation that would have allowed them to digest raw milk’s dominant sugar, lactose, after childhood.

Today, however, 35 percent of the global population — mostly people with European ancestry — can digest lactose in adulthood without a hitch.

So, how did we transition from milk-a-phobics to milkaholics? “The first and most correct answer is, we don’t know,” says Mark Thomas, an evolutionary geneticist at University College London in the U.K.

Most babies can digest milk without getting an upset stomach thanks to an enzyme called lactase. Up until several thousand years ago, that enzyme turned off once a person grew into adulthood — meaning most adults were lactose intolerant (or “lactase nonpersistent,” as scientists call it).

But now that doesn’t happen for most people of Northern and Central European descent and in certain African and Middle Eastern populations. This development of lactose tolerance took only about 20,000 years — the evolutionary equivalent of a hot minute — but it would have required extremely strong selective pressure.

“Something happened when we started drinking milk that reduced mortality,” says Loren Cordain, an exercise physiologist at Colorado State University and an expert on Paleolithic nutrition. That something, though, is a bit of a mystery.

Read more…here.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s