"The "walrus" gene"
A mutation has been found that increases resistance to cold
Skeletal muscle fibers can be divided into "fast" and "slow". Due to the increased content of myoglobin, the "slow" muscles have a richer red color, while the "fast" ones remain whiter. The muscle tissue of people is characterized by a reduced amount of white fibers, and some have especially little of it. The fact is that the work of these fibers is partly provided by the protein actinin-alpha-3, and about 20 percent of people carry a mutation that stops the work of the gene encoding this protein.
It is known that this mutation has been spreading since people migrated from Africa to regions with a colder climate. And indeed: recently, Swedish scientists have demonstrated that the loss of actinin-alpha-3 increases resistance to cold and reduces energy costs for maintaining body temperature.
This is reported in an article published in the American Journal of Human Genetics (Wyckelsma et al., Loss of α-actinin-3 during human evolution provides superior cold resilience and muscle heat generation).
The team of Professor of the Karolinska Institute Hakan Westerblad conducted experiments with 42 healthy volunteers aged 18 to 40 years. They were placed in cold (14 °C) water in "sessions" of 20 minutes with 10-minute breaks. In total, the subjects spent two hours in the cold, while the scientists tracked the contractions of their muscles using electromyography (EMG). In addition, muscle tissue samples were taken from them to assess its composition and the content of actinin-alpha-3.
As might be expected, people deprived of actinin-alpha-3 had more "slow" red muscles, and 69% of them were able to maintain body temperature above 35.5°C, whereas only 30% of volunteers with actinin-alpha-3 and a large number of "fast" fibers had such.
Thus, it can be concluded that the absence of this protein increases the body's resistance to cold.
In fact, both types of muscle fibers are able to maintain body temperature. However, the "fast" ones produce this with rapid, sharp contractions, which is manifested by trembling — not the most efficient and quite energy-consuming method. But the "red" fibers warm the body with slow tonic contractions, much more economical.
It is obvious that the mutation that disrupted the synthesis of actinin-alpha-3 and increased the content of red fibers in comparison with white ones was beneficial when ancient people migrated to cold regions. And, of course, it affects personal physical characteristics: "People who lack actinin-alpha-3 rarely succeed in sports that require explosive strength," says Professor Westerblad in a press release One in five has a mutation that provides superior resilience to cold, "but they show better results in terms of endurance."
And the fly in the ointment missed in this translation.
In the same press release, Professor Westerblad said: "This mutation probably gave an evolutionary advantage during migration to a colder climate, but in modern society this ability to save energy can increase the risk of "diseases of abundance"" - VM.
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