Perhaps the most striking episode in human biological evolution we remember about school is the loss of the queue – the existence of which has passed into the collective memory, since we still call it the "queue" where it existed – but it is by no means the only one. . But even more impressive, though unlikely, is the fact that not only human evolution has not stopped, but it can happen even faster than before.
The feeling that things in terms of human physiology are "frozen" is mainly due to the evolution of medicine, which catalytically intervenes in healing, not allowing the natural choice to move to mutations that will allow the body to adapt and survive. Of course, this is, in principle, good. Because epidemics of the past have strengthened the human body against viruses, but this has happened after a truly massive carnage with millions of deaths. And nothing could give you a "place" for the survivors …
As a progression, one notices the gradual change in the DNA of a species over many generations. It can happen with natural selection when certain characteristics created by genetic mutations help an organism to survive. These mutations are transferred to the next generation and gradually become common to the entire population.
According to the Conversation, by studying our DNA, we find evidence that natural selection has made new mutations and changes and continues to do so. Although modern health care, at least in developed countries, has freed us from many causes of death, in countries without access to good health care, people continue to evolve, just to survive. Survivors of infectious disease epidemics lead to natural selection, transferring their genetic resistance to offspring. Our DNA shows elements of a recent process of natural selection for disease-resistant killers, such as Lassa fever and malaria. Natural selection in response to malaria is still ongoing in areas where the disease remains common.
As is well known, people are adapting to their environment. Thus, mutations that allow people to live at high altitudes have become more reasonably prevalent in the populations of Tibet, Ethiopia, and the Andes. In fact, the spread of genetic mutations in Tibet is perhaps the most rapid evolutionary change in humans that has occurred in the last 3,000 years. This rapid increase in the frequency of a mutant gene that increases oxygen content in the blood gives residents a survival advantage at higher altitudes, resulting in the survival of more children.
Diet is another source of adjustments of the human body. Inuit DNA data from Alaskan, Greenland and Canada show a recent adaptation that allows you to seamlessly process the high-fat food from Arctic mammals, which would be a huge challenge for more "sophisticated" stomachs.
Studies also show that natural selection favoring a mutation that allows adults to produce lactase – the enzyme that breaks down milk sugars – to lactose – is because certain groups of people can digest milk after weaning during childhood. age. More than 80% of Northwest Europeans can do this, but in parts of East Asia where milk is not very popular, lactose digestion is the norm. Like the high altitude setting, natural selection for milk assimilation has evolved more than once in humans and may be the strongest type of recent choice.
To the joy of junk food companies and the resentment of environmentalists and nutritionists, The Conversation report suggests that we can also adapt to unhealthy foods. A study of genetic changes in the US during the 20th century found the choice of lowering blood pressure and cholesterol as a defense of the body in the modern "plastic" diet.
The "cliff" and the "creek" …
However, despite these changes, natural selection affects only about 8% of our genome. According to the "neutral evolution" theory, mutations in the rest of the genome can be modified in populations, but by chance. The scheme is as follows: If natural selection is impaired – through, for example, continuous progress in medicine – the mutations that would normally disappear will not disappear, which could increase its frequency and thus increase the rate of progression. .
But the theory of "neutral evolution" can not explain why some genes evolve much faster than others. We measured the speed of genetic evolution by comparing human DNA with that of other species, which also allows us to determine which genes are growing rapidly only in humans. For example, a rapidly evolving gene is HAR1, which is needed in the development of the brain. A random portion of human DNA is on average more than 98% identical to chimpanzee DNA, but HAR1 evolves so rapidly in humans that it is now about 85% with the chimpanzee.
Scientists are seeing these changes, but they still do not fully understand why rapid evolution occurs in some genes, but not in others.
As it turns out, the process of evolution does not just happen with natural selection and it is definitely not likely to ever stop. Releasing our genomes from the pressures of natural selection opens the way for other evolutionary processes, making it even more difficult to predict what and how future people will be. At the same time, if the protection of the modern medicine organization functions with such a catalytic role in evolution, there will likely be more genetic problems for future generations.
Of course, even so, which geneticist could really support today … let the epidemics "get the job done"?