An analysis of ancient human skeletons finds that an increase in size and weight in some regions coincided with the rise of lactose tolerance


20 January 2023

By Luke Taylor

Person milking a cow

Milk is a rich source of energy and nutrients

Atlantide Phototravel/Getty Images

People in northern and central Europe increased in size between 7000 and 4000 years ago, while people elsewhere stayed the same height or got smaller, a study has found.

The growth of some Europeans was probably caused by them evolving lactose tolerance earlier, the researchers say.

The ability to produce the enzyme lactase into adulthood and digest milk is believed to have played a significant role in the health and evolution of ancient humans.

Studies have suggested that those who were able to consume milk without health complications were able to overcome acute famine, making lactase persistence spread through natural selection.

To measure the impact of lactose tolerance on the size of humans, Jay Stock at Western University in Ontario, Canada, and his colleagues collated data on 3507 skeletons from 366 archaeological sites in seven regions – the Levant, southern, central, and northern Europe, the Nile Valley, South Asia and China – going back to 30,000 years ago.

The researchers used skeletal measurements to estimate the specimens’ heights and the size of weight-bearing joints to estimate their weights.

They found that the global mean height for men and women declined from 30,000 years ago onwards, reaching its minimum between 8000 and 6000 years ago. But in central Europe, stature increased between 7000 and 4000 years ago, while in northern Europe it increased between 8000 and 2000 years ago. Similar trends were seen for body mass.

The earliest evidence of dairy production is from around 9000 years ago in western Asia, from where it spread around the world, reaching central Europe at least 7400 years ago.

The authors theorise that the exceptional growth resulted from those European peoples becoming lactose tolerant, which allowed them to gain more nutrition from milk. In other parts of the world at this time, people only consumed fermented dairy goods, such as yogurt and cheese, which contain less lactose.

Although the data can’t prove that lactase persistence was the cause, the researchers argue that it is a compelling explanation. “We’re showing that the timing and the geography of body size increase corresponds with what we see in lactase persistence, and lactose is such an important component of diet as it provides very, very energy-rich, nutrient-rich sources of food,” says Stock.

However, the study found that people in Britain actually got smaller in the same period, despite being early milk drinkers.

“The authors have done some pretty fantastic stuff on stature, estimating body mass and how they changed through time. But I see no systematic, numerical analysis to suggest it is much more than a guess that selection was stronger on lactase at this time when we see increases in body mass,” says Mark Thomas at University College London.

Previous research has suggested that humans became smaller when they abandoned a hunter-gatherer lifestyle to cultivate crops, as relying on a single crop would have been less nutritious.

But the new study found strong evidence that people were getting smaller before they shifted to agriculture, hinting that there was another cause for their declining stature, says Thomas.

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