14 DAY TRIAL // All mammals are born with the ability of digesting milk, due to the presence of an enzyme named lactase that metabolizes the sugar from milk, named lactose.
But after the weaning, the gene that encodes the lactase is shut down and most mammals lose the ability to digest milk; the undigested lactose can inflict many gut problems.
In some cases, a mutation can keep the lactase gene functional the whole life of an individual, a property named lactase persistence. This phenomenon happened also with the human populations, enabling them to eat milk and milk products. Even today, half of the human populations cannot digest milk, like in eastern China, Japan, southeast Asia or indigenous tribes in Americas and Oceania.
A new research at University College London that investigated ancient DNA from fossil bones shows that this ability arose in European populations relatively recently, no more than 8,000 years ago.
There are some theories trying to explain how the European populations developed lactase persistence.
The culture-historical one sustains that shortly after the domestication of livestock, a few individuals possessing the lactase persistence mutation had an advantage towards the other, as the new aliment was rich in proteins, fats, vitamins and calcium, and natural selection favored these individuals and their offspring.
Another theory says that ancient Europeans had already presented a high incidence of lactase persistence when livestock was domesticated.
The team investigated nine fossil skeletons from five archaeological sites located in central, northeast, and southeast Europe. Eight of the skeletons were 7800-7200 years old and one was 3800 years old. The team searched for genetic mutations commonly linked with lactase persistence in European populations, a kind of lactase persistence mark. None of the individuals carried the mark, so the culture-historical theory seems to be true. "The key point here is that there was something that was very, very rare 8000 years ago but common today," says Mark Thomas, an evolutionary geneticist and an author of the study. "That's really strong natural selection."
If the data are true, "then I think it does lend credence to the [culture-historical] hypothesis," says Hendrik Poinar, an evolutionary geneticist at McMaster University in Ontario, Canada. But he warns that more skeletons should be investigated to give more fundament to this issue.