A new study has shown that consumption of animal milk in some parts of the world between 7,000 and 2,000 years ago led to increases in human body mass and stature in those regions.

This ran counter to body size trends in other parts of the world during that time where milk drinking was not as prevalent.

The size increase is found in regions where there was evolution of higher frequencies of genes that allow humans to produce enzymes to digest milk into adulthood, which is known as lactase persistence.

The study, led by the University of Western Ontario – often known simply as Western University – in Canada, and involving 16 researchers, compared the stature and body mass of 3,507 skeletons from 366 different archaeological sites, ranging across 25,000 years.

Farming developed in different regions of the world at different times. Migrating farmers brought crops and dairy producing animals with them to parts of Eurasia occupied by hunter-gatherers.

In some regions, including central and northern Europe, crops from western Asia did not thrive, and humans moved from producing yoghurt and cheese, which have lower amounts of lactose sugar, to direct consumption of raw milk, which has much higher levels of lactose.

The ability to digest higher quantities of lactose led to greater energy availability from dairy products. In regions where there is genetic evidence for increased milk consumption, there is also increases in body stature and mass, the study found.

The trends of ancient milk consumption can still be seen today in different frequencies of lactose intolerance across various population groups.

The study was led by Prof. Jay Stock, a biological anthropology professor at Western University.

He commented: “That process of evolution led to the pattern of lactose intolerance that we see today, where people in the north of Europe are more frequently lactose tolerant [are able to digest lactose] than people in the south of Europe.”

According to Prof. Stock, dairy products are an important component of diets in many parts of the world, and higher frequencies of lactose tolerance that evolved in some regions of Africa and Asia are examples of convergent evolution, meaning it evolved separately from Europeans.

The data set used in the study is primarily based on European samples, which Prof. Stock said is because of historically more archeological exploration in Europe.