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Thursday, December 11, 2008

Neanderthals Were Lactose Intolerant

I'm written many times that the ability to drink milk as an adult is a recent cultural phenomenon. All mammals who manufacture lactose as the sweetener for their mother's milk produce the lactase enzyme, the one that digests lactose, only up through the age of weaning. After that the lactase production stops, since the body naturally thinks that the animal won't drink any more lactose after being weaned from it.

Nature didn't reckon with humanity's ingenuity. For one thing humans developed ways of milking other mammals. And they fermented or cultured the milk so that it would last longer in warm climates, making products such as yogurt and kefir and cheese. Yogurt and kefir and cheese also happen to be naturally much lower in lactose than regular liquid milk.

So people started eating dairy products.

Here's another odd fact about the human body. A small percentage of humans have a spontaneously mutated gene on Chromosome 2. That mutated gene never sends the signal to turn off lactase production. That means that those people can have all the dairy products they want, even regular unprocessed milk, all their lives.

Milk, no matter how many crazy claims you hear, is a really healthy product, full of vitamins and nutrients, especially calcium. People who can have loads of milk tend to be healthier than those who don't. It's not a huge difference, but even if only 5% of the population with the mutated gene out-reproduces the rest of the populations, the mutant gene will spread rapidly, in historic time.

That's why northern Europeans tend to be lactose tolerant. It all started around 10,000 years ago, with the first instances of dairying and herding and milking and milk processing. Before that time you would expect almost all humans to be lactose intolerant. Natural selection would have no pressure to drive the mutant gene through any population.

Can we get any confirmation of this hypothesis?

Just out is a statement that Scientists have decoded half of the Neanderthal genome. The Neanderthals, another species of humanity that are now thought to have been wiped out by modern humans, died off well more than 10,000 years ago. And analyses of 38,000-year-old Neanderthal DNA "suggest that Neanderthals were lactose intolerant, hardly surprising since the ability to digest dairy products in adulthood only became common in humans after the domestication of cows, 10,000 years ago."

Homo sapiens and Homo neanderthalis probably didn't interbreed, and the Neanderthals didn't evolve into us. We were two different species that happened to share the earth at one time. We outcompeted them. Happens to animals all over the world in every time in history.

That either makes us very special or very ordinary. Let the philosopher in you decide which.

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