It’s a popular example in biology class of how culture influences evolution: the development of human lactose tolerance. It is said to be most common in areas with a long tradition of livestock and dairy farming. This suggests that the beginnings of animal milk consumption coincided with the spread of the genetic changes required to digest milk in adulthood. However, the authors of a current study in »Nature« are now questioning precisely this connection.
The modeling of genetic and archaeological data did not show a clear link between milk consumption and the increase in lactose tolerance, writes the team led by Richard P. Evershed, George Davey Smith and Mélanie Roffet-Salque from the University of Bristol. Instead, they found that famine and certain pathogens better explain the development of the enzyme lactase, which is necessary for digestion.
First indications of lactose tolerance as late as 1000 BC. Chr.
They created a comprehensive map of prehistoric milk consumption by analyzing 6,899 animal-derived fat residues found on 13,181 pottery fragments from 554 archaeological sites. The results suggest that milk consumption was widespread in Europe since the Neolithic (from around 7000 BC), but varied by region and time. The 106 researchers also examined the frequency of the major variant of the lactase persistence gene among Eurasians over time, based on existing DNA data from 1786 prehistoric European and Asian individuals. Their results show that lactose tolerance did not develop until around 1000 BC. was widespread.
Infants and young children naturally produce lactase; the enzyme breaks down the lactose molecule into two digestible sugars, allowing infants to consume breast milk. Until about 3000 years ago, however, this ability was usually switched off after weaning. Today, around a third of the world’s population can be classified as lactose tolerant, predominantly in Northern Europe. Using their analysis of contemporary health data from the UK, the authors show that the ability to digest milk does not appear to confer an advantage in terms of evolutionary fitness (measured by traits such as life expectancy or child rearing).