There’s nothing like reading in The New York Times that you are unevolved. Especially when you read it over breakfast, just starting your day and hoping it will be a good one. It’s quite a blow.

According to an article in the good old Times (“Study Detects Recent Instance of Human Evolution”), scientists have detected what they see as a sign of recent human evolution: the ability to break down milk sugars in adulthood.

Throughout most of human history, the ability to digest lactose, the principal sugar of milk, has been switched off after weaning because there is no further need for the lactase enzyme that breaks the sugar apart. But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.

What we find, then, is an example of environmental factors (the raising of cattle) interacting with genetic evolution. It’s like those moths we all learned about in high school biology class. The ones that lived during the industrial revolution. These moths, Lepidoptera, were almost always light-colored. When the industrial revolution coated all the trees in soot and killed of all the lichen, the light-colored moths were exposed and eaten by their predators. However, a mutation had occurred that produced some dark-colored peppered moths, and those ones survived. Today, apparently, lepidoptera tend to be dark-colored, not light. It’s evolution, baby.

So now, scientists are finding that the same thing is happening with adults and milk digestion. But what’s most exciting to them is that it’s happening independently in different places: in Europe (“Almost all Dutch people and 99 percent of Swedes are lactose-tolerant”) and now in parts of Africa. Apparently, separate mutations have occurred in four different places, leading to adult populations in four areas that have a significantly higher percentage of adult milk digesters.

I, sadly, am not one of these digesters. Since I was about 18, I have been unable to digest lactose, the sugar found in milk. Since then, I have taken solace in knowing that a significant percentage of the world’s adult population is lactose intolerant.

According to the National Institute of Diabetes and Digestive and Kidney Diseases (the NIDDK), “Between 30 and 50 million Americans are lactose intolerant.” So I did a little research, and then a little math. Mr. VanHanaghan always told me math would come in handy some day, and finally he was right. According to the 2000 US Census, there were 209,128,094 Americans over the age of 18 in that year. This was 74.3 percent of the total US population.

Assuming a similar percentage today, and taking today’s projected US population into account (the census bureau has an up-to-the-minute population clock at http://www.census.gov/main/www/popclock.html), then there are approximately 223,186,956 people over the age of 18 currently living in the US. That means that the percentage of American adults with lactose intolerance could be as high as 22.4%. That’s almost a quarter of the adult population.

A quarter of the adult American population that is unevolved. I might have guessed at such a percentage, honestly, but I never imagined I was a part of it. How sad.


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