My milkshake brings all the genes to the yard
Damn right, it’s better than yours
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While it might not be as dramatic a superpower as being able to live four kilometres up a freezing mountain, the ability of many humans to drink milk in adulthood is certainly handy.
Most animals can drink milk in infancy, but as they grow the lactase gene that digests lactose, the sugar found in milk, gets switched off. After this point, drinking milk results in a lot of stomach discomfort, diarrhoea, wind and general gastric unpleasantness. But around a third of the global population - especially those of European ancestry like me - have a genetic variation that allows the lactase gene to stay switched on indefinitely, known as lactase persistence, allowing us to chug the white stuff without a problem.
As the story goes - which I covered in my Radio 4 programme Ingenious, about the Milkshake gene - the spread of this gene through populations in some parts of the world coincided with the rise in dairy farming. In turn, this enabled people to get more protein and fat in their diets, grow healthy and strong, and outcompete the non-milk drinking populations around them. It’s a nice example of genetic selection working hand in hand with cultural evolution, helping to shape our human story. But the latest research suggests that this neat evolutionary Just So story may not be true.
A new study published in 2022 provides an alternative timeline. Bringing together an impressive team of more than 100 scientists, including geneticists, chemists, archaeologists and more, the researchers studied traces of animal fats found on ancient pottery indicating dairy consumption together with DNA analysis of ancient skeletons and modern humans.
The results painted a radically different picture of the past, showing that milk-drinking people who were living in Eurasia from around 10,000 years ago, when we know that dairy farming started to get going, didn’t have the genetic variant for lactase persistence. Yet they drank milk anyway. In fact, the persistent version of the gene didn’t start to become commonplace in Europe until around 3,000 years ago. So was everyone just putting up with a runny tummy and farting for thousands of years?
It turns out, probably yes. Although the side effects of drinking milk for those who can’t fully digest it aren’t always pleasant, it’s far from fatal. Until, that is, there’s something more serious to worry about, like famine or disease. If there’s little other food available than milk, or you’re suffering from a disease that’s already weakened your body, then the digestive distress caused by drinking milk could prove fatal. So, during the Bronze age - a time of numerous epidemic diseases and famines - people with the lactase persistence gene variant would have a survival advantage, meaning that it started to spread through the population. Rather than farming being a driver of lactase persistence, famine may have underpinned it instead.
