The human species evolved to withstand the cold of climate change

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A genetic mutation linked to the evolution of the human species. One study states that more than one billion people around the world lack a protein called alpha-actinin-3 found in muscle fibers due to an altered gene; a characteristic that would allow them to be more resistant to cold.

A variant of a gene; a gene very similar to another but which has differences linked to mutations. Researchers at the Karolinska Institute have discovered a particular good that would allow its users to be more resistant to low temperatures. The latter remind us that skeletal muscle (under voluntary control of the nervous system) is made up of fast-twitch muscle fibers and slow-twitch muscle fibers that are more resistant to fatigue. However, the protein alpha-actinin-3, present in fast-twitch muscle fibers, is absent in nearly one in five people, or 1.5 billion people, due to a mutation in the gene that codes for the protein.

The reason is none other than evolution: the prevalence of the mutated gene has increased as humans migrated from Africa to colder climates in central and northern Europe.

"This indicates that people lacking alpha-actinin-3 are better at keeping warm in harsh climates, but before there was no direct experimental evidence for this. We can now show that the loss of this protein increases tolerance to cold and we have also found a possible mechanism for this, "explains Professor Hakan Westerblad.

Body temperature drops less quickly

The researchers proceeded to recruit 42 men between the ages of 18 and 40, with or without the variant. They were allowed to sit in cold water (14 ° C) up to their necks until their body temperature dropped significantly and the experiment ended. Individuals emerged from the bathroom every 20 minutes and rested for 10 minutes at room temperature, then repeated the experiment for the next 20 minutes. This procedure was continued until the rectal temperature dropped to 35.5 ° C or a maximum of 120 min immersion in cold water. The electrical activity of the muscles was studied by electromyography (EMG) and muscle biopsies were taken to study the protein content and the composition of the fiber types.

The results showed that the percentage of individuals capable of maintaining their temperature above 35.5 ° C during total exposure to cold water was higher in the "variant" group (69%) than in the control group (30%). .

Furthermore, the researchers found that the skeletal muscles of people without alpha-actinin-3 contain a higher proportion of slow muscle fibers. When they cooled down, they were better able to maintain body temperature at a certain level: Instead of activating the fast fibers, which cause chills, they tended to produce heat by increasing the core activity (tone) in the slow fibers.

Your muscles react with slower contraction and increased muscle tone by generating energy efficient heat instead of chills. "The mutation probably brought an evolutionary advantage by migrating to a colder climate, but in our modern society, the ability to save energy could mean an increased risk of Western diseases (obesity, type 2 and other metabolic disorders)," notes the professor. Hakan Westerblad - An assumption that the researchers now would like to explore further, especially since their study also found a striking difference between these people and their athletic performance.

How could the lack of this muscle protein alpha-actinin-3 affect the bodys response to physical exercise? According to Professor Westerblad, "People lacking alpha-actinin-3 are rarely really good at sports that require strength and explosiveness, whereas this would tend to increase the ability of these people in endurance sports." However, the scientific team emphasizes that one of the limitations of the study is the fact that in experiments carried out in humans it is more difficult to study the mechanisms with the same level of detail than when they are carried out in animals and cells.

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