A large-scale genetic study has found that ongoing human evolution is facilitating the removal of harmful mutations from the gene pool.
Are we set to live longer and healthier?
Not all mutations are harmful. Some are beneficial, some are harmless, but some can shorten people's lives. Beneficial mutations offer members of a species a better chance of survival. Harmful mutations, meanwhile, are those that predispose people to life-shortening conditions. These conditions include heart disease, obesity, high cholesterol, and asthma. Researchers now say that our ongoing evolution is selecting against these mutations. The mutations are appearing less in people that live longer and are thus more likely to pass their genes on to the next generation. When this happens, beneficial mutations and their adaptive traits become more common in the gene pool.
According to the researchers, the disappearance of these mutations from the gene pool is subtle. However, there is still genetic evidence that modern human populations are undergoing natural selection.
The removal of hamrful mutations may increase our longevity.
Earlier this year, researchers also came to similar conclusions. This newer study, however, approaches the matter from a different angle.
Genetic databases from the US and the UK provided the information for the study. Researchers either recorded a person's parents' age of death, or a person's own age of death in certain cases. This served as a measure of longevity.
The researchers tested over eight million common mutations and found two that became less common as the population aged. One mutation is the variant of the APOE gene and has a strong link to Alzheimer's disease. This gene was rare in women over the age of 70. The other mutation, meanwhile, is a variant of the CHRNA3 gene, which associated with heavy smoking. This became less common in the population starting from middle age. In terms of survival edge, people who do not have these genes are more likely to live longer. These harmful mutations become less rare as the population ages because individuals with the variants tend to have a higher chance of dying at a younger age.
However, this alone does not serve as evidence of ongoing human evolution. Longevity, in evolutionary terms, isn't as important as fecundity. It doesn't matter that you lived a long life if you were unable to pass on your genes. Also, evolution would not need to select against harmful mutations that take effect after the age of fertility.
Are we living longer so we can help care for younger generations?
The researchers point out, however, that if evolution does not need to select against harmful mutations of this nature, there would have found a lot more than just two harmful mutations. This may indicate that natural selection has already weeded harmful life-shortening mutations out of the gene pool.
Still, the question of the necessity of longevity remains. The researchers have two theories to explain the evolutionary advantage of living longer. The first is that living to a healthy old age can enable individuals to care for grandchildren, giving the younger generations a better chance of survival. The second is that these harmful mutations are also harmful earlier in life, just in a subtler way.
According to the researchers, studying ongoing human evolution is difficult. However, studies like this tells us a lot about our biology.
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