Every day we drink the breast milk of other animals – mostly cows. Why though? Benjamin Phelan looked at our relationship with milk:

• In general mammals become lactose intolerant – allergic to milk – once they leave infancy.
• Up until 10,000 B.C. this was true for humans as well. Then somebody, likely a male in turkey, had a mutation that allowed them to continue to process milk throughout their lives.
• Within a few thousand years this mutation either spread, or independently started, in civilization across the planet.
• The strangest thing about this is that even before the mutation we could have consumed milk…as long as we waited for it to ferment into yogurt, something that only takes a few hours. Yet the mutation made ‘fresh’ milk immediately digestible.
• For the mutation to have spread as quickly as it did, it must have conferred extraordinary evolutionary benefits. In particular, it seems that anytime people were concentrated in cities, the mutation began to spring up.
• One explanation is that milk was a guaranteed source of fresh water. Water from a stream might look clean but could still contain disease. If milk came from a healthy animal, it was also probably safe to drink

Read other potential explanations for why we might now be milk drinkers, and more about our history with the drink over here.

Source: Slate