People have not yet been made cooking. We continue to develop and adapt to the world around us, the records of our adaptations written in our bodies.
We know there are some environments that can make us unwell. Mountain climbers often succumb to altitude – the reaction of the body to a significant drop in atmospheric pressure, which means that less oxygen is taken with every breath.
Yet, at a high altitude of the Tibetan Plateau, where the levels of oxygen in the air breathe significantly lower than the lower altitude, human communities are flourishing.
For more than 10,000 years, the region has been settled, the bodies of those living there have changed in ways that allow residents to make the most of the atmosphere, which for most people would not lead to enough oxygen through blood cells to the tissues of the body, a condition known as hypoxia.
“The adaptation to the hypoxia at high altitude is captivating, as stress is severe, experienced equally by all at an altitude and measurable,” said anthropologist Cynthia Bial of Case Western Reserve University in the United States to Sciencealert.
“This is a beautiful example of how and why our species has so many biological variations.”
Beall has been studying the human response to hypoxic living conditions for years. In studies published in October 2024, she and her team presented some of the specific adaptations in Tibetan communities: traits that help blood supply oxygen.
To unlock this discovery, researchers have deepened one of the markers of what we call evolutionary fitness: reproductive success. Women who deliver live babies are the ones who pass their features to the next generation.
The traits that maximize the success of the individual in an environment will most likely be found in women who are able to experience the stress of pregnancy and childbirth.
These women are more likely to have more babies; And those babies who inherited the traits of survival from their mothers are also more likely to survive until adulthood and convey the features of the next generation.
It is a natural selection at work and can be a little strange and contrasting; In places where malaria is common, such as the incidence of sickle -cell anemia is high as it includes a gene that protects against malaria.
Beal and her team have a study of 417 women between the ages of 46 and 86 who have lived throughout their lives in Nepal above the altitude of about 3500 meters (11 480 feet). Researchers have registered the number of live births ranging between 0 and 14 per woman for an average of 5.2, as well as health and physical information and measurements.
Among the things they measured were the levels of hemoglobin, the protein in the red blood cells responsible for the supply of oxygen to the tissues. They also measure how much oxygen is worn by hemoglobin. Interestingly, women who demonstrated the highest degree of live births have hemoglobin levels that are neither tall nor low, but medium to the test group.
But saturation with hemoglobin oxygen was high. Together, the results suggest that adaptations are able to maximize the supply of oxygen to the cells and tissues without thickening the blood -a result that would put more stress on the heart as it struggles to pump a higher viscosity fluid, more resistant to the flow.
“We knew before that the less hemoglobin was useful, now we understand that the intermediate value has the highest benefit. We knew that the greater saturation of oxygen of hemoglobin is useful, now we understand that the more saturation is, the more useful.”
“It was unexpected to establish that women could have many live births with low values of some of the oxygen transport if they have favorable values of other oxygen transport.”
Women with the highest reproductive success also had a high rate of blood flow to the lungs, and their hearts had wider than medium left ventricles, the heart chamber responsible for pumping oxygenated blood into the body.
Taken all together, these features increase the speed of transport and supply of oxygen, allowing the human body to make the most of the low oxygen in the air.
It is important to note that cultural factors can also play a role. Women who are beginning to reproduce young and have long marriages seem to have a longer exposure to pregnancy, which also increases the number of live births, researchers have found.
Even given the physical traits, however, they played a role. Nepalese women with physiologies, most similar to women in an unstressed, low altitude, tend to have the highest percentage of reproductive success.
“This is a case of continued natural selection,” Biel said. “Understanding how populations like these adapt gives us a better understanding of the processes of human evolution.”
The study has been published in Works of the National Academy of SciencesS
A larger version of this article was published in October 2024.