According to a recent study of the genomes of over 200,000 people from the United Kingdom and United States, human beings are still evolving, albeit rather slowly.
Since many people, especially those in wealthy countries, live well beyond their reproductive years, many have come to believe that human evolution had frozen. With medical science now allowing even people with severe health problems to live full lives and have children, more people are able to pass their genes along to the next generation. Yet natural selection still continues to affect the human species, as this study has found.
The study, conducted by researchers at Columbia University, found that a gene variant that is associated with heavy smoking behavior (and the increased risk of a smoking-related death) is becoming rarer. Another gene, this one linked to late-onset Alzheimer’s disease, is also becoming less common. There is also evidence that more people who live to an advanced age- 80 and older- are showing decreased instances of the genes that are linked to heart disease, asthma, high cholesterol, and obesity.
The scientists believe this evidence shows that natural selection is still at play in the human population. This is because these disease-free people have longer lifespans and have a greater chance to pass on their genes to offspring, especially since more people are having children at an older age. In addition, people who don’t smoke heavily, aren’t obese, and who don’t have cardiovascular disease may be able to have more children in the first place. Since these people tend to stay healthier as they age, they may be able to help out more with grandchildren, thus increasing the chance that their descendants are able to reach adulthood and pass on their genes.
Naturally, the results of this study have led some to question if this could mean that Alzheimer’s and other diseases could be eradicated by natural selection. The authors of the study say this is possible, but that it could take many generations before this happens. As the environment continues to change, gene variants that are helpful now might eventually cease to be beneficial. For example, there could be unknown traits associated with the Alzheimer’s gene that could cause a longer lifespan under different conditions. Were those conditions to arise, people with the Alzheimer’s gene could end up passing their genes on more frequently than people without the gene. Until those conditions occur, it is virtually impossible to know which genes will end up being beneficial.
The researchers do hope that large-scale genomic sequencing, like that undertaken in their study, will lead to more discoveries that could eventually help science eliminate conditions like heart disease and Alzheimer’s for good.