Humans are the only mammals on the planet that consume milk from other species. But why? Lucky for you, we took an udder-ly close look at the origins of our milky drinking habits.
Adult consumption of another species' milk only became possible after the domestication of animals. The lactase persistence allele (the series of genes on a chromosome that determine the hereditary characteristics) is thought to have co-evolved with the rise of dairy production and can be traced back to European farmers 7,500 years ago. Mind you, these early Europeans were not yet lactase persistent so they likely experienced a lot of flatulence. Nevertheless, these adventurous folks persisted in drinking milk on the reg and, over time, a mutation occurred in the section of DNA that regulates the lactase gene. It’s unclear why this trait was favored in these populations - scientists theorize it was probably due to a multitude of factors based on where the communities lived, meaning these populations evolved to tolerate milk for different reasons.
So how do we do it? Humans that are breastfed produce an enzyme called lactase which allows them to digest the unique sugar, lactose, found in breast milk (didn’t think you’d be reading about breast milk in your Sunday inbox did ya now). As humans are weaned off of their mother’s milk, they typically stop producing lactase. However, humans from predominantly pastoral communities - those that raised livestock vs. hunter-gatherers and forest-gardeners - eventually evolved to be lactase persistent, meaning the critical lactase enzyme remained active into adulthood. Today, lactase persistence varies widely around the world. The good news is that cheese has lower levels of lactose than milk - which might explain its meteoric rise to fame and fortune.