The History of Milk
Fascinating article in Nature about how our ability to consume milk evolved due to a chance genetic mutation that spread through the population, and shaped human settlement across a continent. You can read the full story here.
Even as recent as the last Ice Age, milk was essentially a toxin for adults. This is because young children produce the lactase enzyme that helps them digest the lactose in breast milk. But as they mature, the gene switches off. Even now, only 35% of the population can digest lactose as adults. Think about it; a tiny change, from a C to a T, changed our diet and changed our distribution across the planet.
“Most people who retain the ability to digest milk can trace their ancestry to Europe, where the trait seems to be linked to a single nucleotide in which the DNA base cytosine changed to thymine in a genomic region not far from the lactase gene. There are other pockets of lactase persistence in West Africa, the Middle East and South Asia that seem to be linked to separate mutations”
Image credit: Leonardi, M., Gerbault, P., Thomas, M. G. & Burger, J. Int. Dairy J. 22, 88–97 (2012).
Inspired by this post, Peter Smalley did some digging to find a similar distribution map for alcohol tolerance as determined by various mutations of the alcohol dehydrogenase enzyme. Yay for inspiring collaborative SCIENCE posts!
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