Friday, July 31, 2015

I Have a Mutant Power (and So Do You Maybe)

A while back I blogged about mutant humans with enhanced abilities like stronger than normal bones. I neglected to point out that I myself have a mutant power. Can you guess what it is? Hint: it’s a very common one.

Answer: I have the ability to digest lactose as an adult.

Lactose is a sugar found in milk, and the ability to digest it is useful as an infant when mother’s breastfeed their babies. Something called the LCT gene provides instructions for making lactase, an enzyme that helps people digest lactose. When infants get older, nature deems they no longer need lactase and as infants get older they gradually lose the ability to digest lactose due to the LCT gene not being expressed so much (that is, the gene becomes gradually less “active”), at least, that’s how it is for many people who don’t have the mutation to keep it being expressed.

The ability to digest lactose is actually the result of a fairly recent mutation in humans. How recent? Roughly 10,000 BCE but it didn’t start to really emerge until about 7,500 years ago in Europe (in evolution terms, that’s a slight twitch of the clock), and not everyone has the full ability to digest lactose; about 65% of people have some form of lactose intolerance (the inhibited ability to digest lactose can range from mild to severe). This isn’t to say that people didn’t consume dairy products before then though. People fermented milk to make cheese or yogurt which reduces the lactose in amounts that they could tolerate. With those who were severely lactose intolerant, which was quite a few people before the mutation spread, drinking milk made people very ill. The ability to digest lactose as an adult gave people a selective advantage, though exactly why the mutation spread so quickly (in evolution terms) is currently unknown.

Still, it’s a remarkable fact of evolution that such a recent mutation in human beings spread as widely as it did, and we can point to this example to show that even among humans evolution is real.