Researchers have found that Europeans have consumed milk without lactase for thousands of years, despite some mild symptoms, and scientists argue that lactase mutation has become important for survival only when Europeans have experienced epidemics and famine, which could exacerbate stomach disorders, leading to life-threatening diarrhoea.
In mammals, females produce milk to feed their babies. Children who are breastfed are digested with an enzyme called lactase. This enzyme splits milk sugar into easily absorbed fragments. Once they're done, young mammals stop producing lactase. After all, why waste energy on producing an enzyme that you don't need anymore?
We know that billions of people around the world are carriers of genetic mutations that allow them to produce lactase throughout their lives, which makes it easier to digest milk.
Scientists have long suspected that the consumption of dairy products and the persistence of lactase have evolved together in human history, and the theory is that when our ancestors began to produce animals some 10,000 years ago, those who had a mutation to sustain lactase received a new source of calories and protein. Those who do not have mutation would have become sick in an attempt to eat it.
A new study suggests that the work led by the biogeochemist Richard Evershed of Bristol University was published in a magazine.
Early Europeans used milk without lactase.
As part of the study, scientists analysed traces of milk left on thousands of pieces of ceramics in Europe and neighbouring regions, so they were able to create a map of milk consumption over the past 9,000 years.
The earliest evidence of milk appeared in Turkey, then these farmers were expected to move to Europe some 6,000 years ago, taking their livestock with them, and during this period the team found that some societies consumed milk and others did not, and they also found that milk production had gone through cycles of expansion and recession over centuries.
In the course of the work, a genetic analysis was also carried out: Mark Thomas and his team, a geneticist from the University College of London, analysed DNA collected from 1,786 ancient skeletons found in Europe and neighbouring regions, with the aim of highlighting mutation that could preserve the gene of lactase active at an adult age.
The oldest mutation they discovered was believed to be about 6,600 years old, but until 4,000 years ago it was rare, in other words, for 2,600 years Europeans consumed milk, but almost none of them were able to produce lactase at an adult age.
To find out how this mutation affects people today, researchers have studied the British Biobank, a database that stores medical records of hundreds of thousands of British volunteers. The analysis showed unexpected results: people without lactase mutation consume about as much milk as people with mutation, but people who cannot produce enzyme do not suffer from additional health problems.
If that is the case today, it probably was then, and some of our ancestors may have suffered from unpleasant spasms and gases, but it wasn't enough to affect their health.
The use of milk without lactase would have been much more risky during the crisis. It has been shown that famine or epidemics can turn mild symptoms into more dangerous symptoms, such as diarrhoea. During the Bronze Age famines, people may have tried to survive by using milk when other foods became scarce. Those who did not have a lactase gene would probably have died of diarrhoea, while lactase mutation could have helped others survive.