It is a example of how culture affects evolution in biology lessons: the development of human lactose tolerance. It is most common in areas with a long tradition of cattle and dairy farming, it is said. From this it can be concluded that the beginnings of consumption of animal milk took place at the same time as the spread of the genetic changes that are necessary for the digestion of milk in adulthood. However, the authors of a current study in "Nature" now question this connection.
The modeling of genetic and archaeological data did not result in a clear connection between milk consumption and the increase in lactose tolerance, the team led by Richard P. Evershed, George Davey Smith and Mélanie Roffet-Salque from the University of Bristol. Instead, the researchers found that famine and certain pathogens explain the development of the enzyme that is necessary for digestion better.
The first evidence of lactose tolerance appeared only in 1000 BC.
To do this, they created a comprehensive map of prehistoric milk consumption by analyzing 6899 fat residues of animal origin, which come from 13 181 ceramic fragments from 554 archaeological sites. The results indicate that milk consumption in Europe has been widespread since the Neolithic (from around 7000 BC), but varied depending on the region and time. The 106 researchers also examined the frequency of the main variant of the Lactase Persistency among the Eurasians over time, based on existing DNA data from 1786 prehistoric European and Asian individuals. According to their results, lactose tolerance was only around 1000 BC. BC spread.
Infants and young children naturally produce lactase; the enzyme breaks down the molecule of lactose into two digestible sugars, so that infants can consume breast milk. However, until about 3000 years ago, this ability was usually lost after weaning. Today, about a third of the world's population can be classified as lactose-tolerant, mainly in northern Europe. Based on their analysis of current health data from the United Kingdom, the authors show that the ability to digest milk does not seem to offer any advantage in terms of evolutionary fitness (measured by characteristics such as life expectancy or offspring).
They therefore propose two alternative ways to explain the increase in lactose tolerance: either it was an adaptation to a food shortage or an increased exposure to pathogens. In both cases or in a combination of the scenarios, the ability of the individual to change their diet and to do without food such as grain or meat and to replace them with dairy products could have been of great advantage.
The results of the study challenged the prevailing explanation for the development of the lactase persistence gene and offer new prospects for future research on other plausible hypotheses, the authors conclude.
