Digesting lactose is pretty weird
But it's just another genetic quirk, really. Plus: what that has to do with a book I reviewed, and some interesting science links from around the web.
Over the last few years, I started having trouble digesting milk. This isn’t uncommon. So uncommon, in fact, that most adults cannot digest lactose.
Lactose digestion only evolved relatively recently. In 2022, scientists in the UK estimated that until about 5000 years ago, no adult humans could digest milk properly. But around that time, Europeans started to evolve the genetic trait for lactase persistence. The enzyme lactase is what makes it possible to digest lactose from milk, but it’s usually only present in children.
To keep the enzyme as an adult is a genetic quirk. Mark Thomas, a UCL professor who co-led the 2022 study on the history of lactose intolerance, explained that it might have been driven by famines:
“If you are healthy and lactase non-persistent, and you drink lots of milk, you may experience some discomfort, but you not going to die of it. However, if you are severely malnourished and have diarrhoea, then you’ve got life-threatening problems. When their crops failed, prehistoric people would have been more likely to consume unfermented high-lactose milk – exactly when they shouldn’t.”
So people with this genetic variant survived famines, and were more likely to reproduce, which kept the genetic variant in the DNA of people from this part of the world.
Sounds interesting from a genetics point of view, right? Well, it turns out that it’s also interesting for people who hold racist beliefs, because they see the ability to digest milk as a uniquely white trait. They really latch on to the “European” part of the story, to the point where the ability to drink milk is seen as a sense of pride among white supremacists. (Would they think I’m less white now that I can no longer digest milk properly?)
I only found out about that last part because I recently reviewed the book “What We Inherit” for Undark. In this book, Sam Trejo and Daphne Martschenko describe how genetic research feeds into genetic myths. They mentioned the fact that scientific articles about the genetics of lactase persistence are cited by racists online as one example of this. It’s just a few pages in the whole book, and one sentence in my review, but it’s the bit that really stuck with me.
There is nothing particularly “white” about digesting milk: it’s just a coincidence that the people who evolved this trait also evolved a lighter skin than the rest of the world. Both are distantly linked to what life in Europe was like many centuries ago (with livestock but without much sun) but I don’t think that’s anything to be proud of, per se. It’s just a genetic record of what happened thousands of years ago.
“What We Inherit” is about those differences in the way that people interpret science and why it’s worth being very careful when using genetic information in the social sciences. It’s an interesting book, and you can read my full review over at Undark.
The Mixture archives are (partly) open now
If you’re a free subscriber, you can now see the archives going back 3 years. Paid subscribers still have the benefit of seeing past the paywall on occasional longer posts.
Science on the internet
Tabletop role playing games make science an adventure. By Shelby Bradford for The Scientist
Coffee crops are dying from a fungus with species‑jumping genes – researchers are ‘resurrecting’ their genomes to understand how and why. By Lily Peck for The Conversation
The origins of agar. By Corrado Nai for Asimov Press
Dead mosquito beaks make surprisingly good 3D printing nozzles. By BoingBoing contributor Ellsworth Toohey
Coral reef food chains cut short by human activity. By Payal Dhar for C&EN