When a mutation that can improve individual viability or fertility occurs in a populationgeneThe mutant gene will eventually spread throughout the population.This selection is called positive selection.
so-calledNegative selectionWhen a harmful gene appears in a population, individuals carrying the gene will be eliminated from the population due to reduced viability or fertility, which is also called purifying selection.Positive selection is an important basis for adaptation to evolution, because this selection method isDarwinismThe root ofDarwinchoice.According to the theory of evolution, human beings andchimpanzeeHad a common ancestor.But since the ancestors of humans and chimpanzees parted ways, how the subsequent evolutionary process affected the genetic changes of both has been a concern of scientists.U.S.AUniversity of MichiganIn order to solve this scientific mystery, the researchers of.The study found that only 154 genes in humans had positive selection signs, while 233 genes in chimpanzees.
The research results of the University of Michigan have overturned the previous conclusion that human beings who are dominant on the earth must experience more positive choices.Researchers believe that this may be due to the fact that chimpanzees have a large number in history, while humans have a small number and live in scattered places. Human genes are mostly caused by random and unstable variations.
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Positive selection refers to the selective effect of nature on living things.Let the fittest survive and the unfit be eliminated.This kind of understanding was first put forward independently by Darwin and Wallace.along withgeneticsWe also have a deeper understanding of the concept of positive selection.It is recognized that the unit of evolution is not an individual but a population, and the role of selection is ultimately reflected by the change of genotype frequency and gene frequency in the population.
According to the change of gene frequency in the population, positive selection can be divided into three types.
① Stable selection: occurs under the condition of relatively stable environment, with a few extremesvariationThe gene frequency in the population changes little, and the biological traits tend to be stable.
② One way selection: when environmental conditions change in a certain direction, individuals at one extreme are saved and individuals at the other extreme are eliminated, which makes the frequency of a certain allele in the population increase generation by generation, while the relative allele frequency decreases generation by generation, resulting in the whole population changing in a certain direction.For example, in the process of industrialization, black moths replaced gray moths.
③ Split selection: extreme variation has different adaptability under different environmental conditions, which leads to population differentiation, geographical race or subspecies formation.This selection method is conducive to producing two or more different species from one species.
It can be seen that selection has an important impact on the change of gene frequency in the population, and the significant change of genotype frequency and gene frequency in the population means the evolution of organisms.Therefore, positive selection is the main driving force of biological evolution.[1]
