A new study suggests that ongoing natural selection keeps damaging mutations from accumulating in the human gene pool.
Humans undergo a lot of genetic mutations. Some mutations are beneficial, like those that allow us to live in the immediate conditions of our environment. Many other mutations, meanwhile, are harmful.
Researchers have found that as damaging mutations accumulate in an individual, there are fewer chances that the individual will be able to procreate. Thus, there are fewer chances that the mutations will appear in the next generation.
Scientists estimate that every human being has about 70 mutations that their parents did not have. Thus, each damaging mutation leads to more and more effects. This can then prevent an individual from passing on genetic material that could be harmful to the next generation.
To study how natural selection works against harmful genetic mutations, researchers analyzed mutations in population samples from Europe, Africa, and Asia. They found that individuals with a large number of harmful mutations are less likely to reproduce and pass on their genes.
The researchers thus theorized that if a new mutation appears in an individual that already has a large number of harmful mutations, the new mutation will be more powerful.
Both natural selection and mutation are basic evolutionary mechanisms. Because the environment is finite, populations can't grow unchecked. This means that not all individuals in a species will be able to reproduce. Certain situations, like the appearance of damaging mutations, will prevent certain individuals from reproducing, while those who are able to survive these situations will be able to have progeny. These survivors, who have the traits to survive in their environment, will be able to pass those traits on to the next generation.
Thus, natural selection ensures that harmful genetic mutations won't get passed on to the next generation. It also ensures that these mutations won't spread through the gene pool. The researchers also found that sexual reproduction is more effective than asexual reproduction in purging these damaging mutations. Sexual reproduction leads to the combination of two genomes. This means that there's a chance of generating a new genome that has few damaging mutations. Asexual reproduction, however, doesn't have the opportunity to produce a genome with fewer mutations.
The researchers also say that sex provides an evolutionary advantage. Sex had to develop in humans and other species to make natural selection more effective. Without sex, we'd have an unsustainable mutation rate.
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