Evolution continues

New technologies allow us to see the evolution of man in action

A. Sokolov, Anthropogenesis.roo

In a new study published in Science (Field et al., Detection of human adaptation during the past 2000 years), an international group of geneticists reconstructs the evolution of man, which took place not in the Stone Age, but literally in recent centuries.

Studies comparing the DNA of many people allow us to trace evolutionary changes, but until recently it was possible to do this with not very high resolution. Usually evolution is visible for tens of thousands of years, because changing a certain part of DNA is not a fast process. New methods of comparing whole genomes allow us to study evolution in short time intervals and show that natural selection has changed the appearance of man even in the last 500 years.

So, the researchers turned to the UK10K project database ("10 thousand British DNA") and took 3195 genomes from it to find out how evolution has changed the British over 2000-3000 years (about 100 generations). 4.5 million point mutations occurring in modern residents of the UK with a frequency of more than 5% were analyzed.

The evolution of the British has even affected freckles. Photo source – picworld.ru

Comparing the rate at which gene variants spread, experts found a number of cases of rapid changes under the influence of natural selection.

How do geneticists determine that they are dealing with selection? The fact is that the genome is constantly changing – the frequencies of genes vary under the influence of random processes, and the speed of these changes is known. But if geneticists see that the frequency of some variant changes 10 or 100 times faster, this is clearly not an accident.

One such example is the evolution of the gene responsible for the synthesis of lactase. Lactase is an enzyme that participates in the assimilation of milk sugar, and without it we would not be able to drink milk. The evolution of this enzyme is one of the best studied examples of evolutionary changes in humans. Young children have a lot of lactase, and they digest milk without any problems. In adult mammals, the lactase gene is switched off, and the enzyme synthesis stops – an adult does not need milk, so trying to drink milk leads to diarrhea and other gastrointestinal troubles. But in some human populations – in those where dairy farming was practiced – a mutation is often found that allows milk to be absorbed at any age. Since goats and cows have become human companions relatively recently, it is not surprising that a variant of the lactase gene that works in adults has spread rapidly in humans in recent millennia. The study showed that this is exactly the case among the inhabitants of Britain.

In addition, the researchers found a proliferation of alleles associated with lighter pigmentation.

No, we are not talking about the skin – apparently, light skin has already become ubiquitous in Europe 2 thousand years ago – but about the color of hair and eyes, and even about the alella responsible for the appearance of freckles.

Above we talked about traits, each of which is encoded by one specific gene. But most human properties are regulated not by one or two, but by dozens or even hundreds of genes distributed throughout the genome.  For example, scientists have identified about 700 genes that affect our growth. It is known that northern Europeans are more likely to have genetic variants associated with high growth than residents of southern Europe. New techniques have made it possible to observe such a multigenic evolution, when a trait changes as a result of the evolution of many genes, the changes of each of which are hardly noticeable – but in total they give a significant effect. The study showed that over the past 2-3 thousand years, natural selection has led to the spread of gene variants associated with higher growth among Britons. What processes is this related to? Maybe the tall Britons liked women more, and therefore left more children? The study does not give such an answer, but only states a fact. Similarly, scientists have found the spread of alleles associated with an increase in the head circumference and weight of infants, later puberty in women, and some others.

So, geneticists have shown that contrary to popular opinion, human evolution has not stopped, and natural selection continues to work. At least, it has been working for the last thousand years.

Portal "Eternal youth" http://vechnayamolodost.ru  21.10.2016