Milk was off-limits just a few thousand years ago

Jan 30, 2014 10:38 GMT  ·  By

Since our species first evolved, until about 10,000 to 11,000 years ago, consuming milk and other dairy products was impossible, since doing so always resulted in an upset stomach. Around the time agriculture developed, our ancestors suddenly became capable of processing lactose, and scientists now want to learn why. 

“The irony of working in this field is that we know what happened, but we don't know how it happened,” says researcher Oddný Sverrisdóttir, the leader of a new study on this complex issue.

She holds an appointment as an evolutionary biologist with the University of Uppsala, in Sweden. Details of her work were published in the latest issue of the journal Molecular Biology and Evolution.

Researchers agreed some time ago that the DNA changes which enable lactose tolerance are relatively new to our species. They first developed within a group of Europeans making up around a third of the continent's entire population at that time. The real questions here are how and why that happened.

Potential explanations as to why lactose tolerance appeared range from becoming better able to survive famines to gaining enough calcium and vitamin D. However, the work Sverrisdóttir and her team conducted recently suggests another explanation.

She proposes that the genetic traits which enable lactose tolerance developed in response to people eating more and more processed dairy products, such as cheese. Even though our ancestors were not yet fully capable of processing this food, they ate it whenever crop failures occurred, in order to avoid starvation.

“The common point between the various hypotheses […] may be that milk may have been an important source of nutrients in the early development of agriculture,” the Swedish research goes on to explain, quoted by NPR.

Her study is based on analyses conducted on DNA samples collected from a series of bones belonging to farmers who lived in northern Spain around 5,000 years ago. The investigation revealed that none of the 8 specimens the group studied featured genes allowing them to process milk.

However, nearly a third of the general Spanish population today is capable of consuming lactose, meaning that the mutations spread like wildfire through its ranks within just a few thousand years. This rate is extremely high by evolutionary and genetic standards.