Despite its benefits, drinking milk into adulthood, let alone other animals' milk, is a strange behavior in the animal kingdom. What makes it even stranger is that an estimated 68 percent of the global human population is actually lactose (乳糖) intolerant. Scientists are still getting to the bottom of why the practice began and continued. This research could unlock new understandings of our food cultures and even our DNA．

The earliest evidence of animal milk drinking dates back almost 

9. 000 years to modern-day Turkey near the sea of Marmara. where milk fats have been found on ancient pottery. According to Jessica Hendy. a scientist at the University of York. then milk would have been part of a diverse diet for it was mixed with other food. From its origins, the technology of making use of milk spread into the Caucasus and then across Europe. By the Bronze Age, people may have been using cow's milk to feed their babies.

For a long time, researchers believed that milk drinking changed as a cultural practice hand in hand with the spread of genetic mutations (变异) that allowed people to tolerate milk into adulthood. But one recent finding suggests milk drinking occurred before these mutations and might not even require them. In Europe. people appear to have been drinking milk for thousands of years before any genetic ability to drink milk became common. The ancient cheese making equipment might offer part of the solution: Fermenting (发酵) milk into yogurt. cheese, or other products reduces the amount of lactose. In Mongolia. researchers have not yet found a genetic mutation that allows people to digest lactose, despite the major role of milk in that culture. So some scientists held that there might be other potential factors helping. 

What we do know about the history of milk reveals how wrong-headed one-size-fits-all nutritional guidance can be. In modern America. milk drinking has been presented as a universal good. In reality, how milk is prepared can change the nutritional picture, and how much our bodies process depends, at least in part. on our own genes.