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Drinking Milk
In 2007, an international team of scientists went to Africa with a question: what caused the majority of Africans to be able to drink milk?
This question may seem silly, but it is something that researchers have been investigating around the world. This is because not everyone can digest the primary sugar in milk, which is called lactose. A protein called lactase is responsible for breaking down lactose, cutting the lactose molecule in two. Babies are born with this protein functioning so they can digest milk.
However, research has shown that in our early ancestors, the genes that produce lactase somehow got switched off after babies stopped drinking their mothers’ milk. In some people today, their genes that code for lactase are still switched off as they become adults. These people are lactose intolerant, which means they cannot digest lactose.
However, in some populations around the world today, there are many people who are able to drink milk as adults because their bodies continue producing lactase.
So what makes this possible? The answer is mutations, which are permanent changes to an individual’s DNA. The scientists investigating their question gathered samples of DNA from people living in the region and looked for structural changes to the genes that coded for the protein lactase.
Structural Changes to DNA
Babies are born able to digest milk. However, some people lose that ability as they grow up. Mutations are relatively common. A mistake occurs every 100,000 or so nucleotides, resulting in about 120,000 mistakes each time a cell divides. The cell is able to repair most changes, but sometimes a change gets through. If a change occurs in an egg or sperm cell, it will be passed down to offspring.
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