Scientists now know of a milkrelated mutation (变异) in our genes—the chemical instructions for life that we carry in almost every cell in our bodies.People who have a mutated form of one particular gene can drink milk just fine.People without the mutation tend to get sick from milk.
To figure out where,and possibly why,milk drinking started,some scientists have been looking at who has the milkdigesting mutation today.Patterns are striking.
Most adults in Northern and Central Europe are able to digest milk—and they do.Cheese,butter and other dairy products are popular in countries such as Sweden,Denmark,Germany and England.Because European settlers dominated North America,most people here can handle milk just fine,as well.That may explain why ice cream is such a popular dessert in the United States.
In much of Africa,Asia and South America,on the other hand,people tend to avoid dairy products because they lead to diarrhea (腹泻) and other stomach problems.(That’s why you won’t typically find cheese on the menu at a Chinese,Japanese or Ethiopian restaurant.) Native Americans are also unable to digest milk.
Based on these genetic patterns,scientists have long thought that milk drinking started in Northern Europe,where dairy is an institution and the milkdigesting mutation is everywhere.
A recent study painted a different picture.With a computer model,Thomas and colleagues looked at the spread of the milkdrinking mutation,farming and other related factors.Working backward,the scientists concluded that the first milkdrinkers lived in Central Europe around what’s now Hungary about 7,500 years ago.The practice didn’t start farther north,as scientists had thought before.
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