In a study analyzing the genomes of 210,000 people in the United States and Britain, researchers at Columbia University found that the genetic variants linked to Alzheimer's disease and heavy smoking are less frequent in people with longer lifespans, suggesting that natural selection is weeding out these unfavorable variants in both populations. The results appear in today's PLOS Biology.
The researchers analyzed the genomes of 60,000 people of European ancestry genotyped by Kaiser Permanente in California, and 150,000 people in Britain genotyped through the U.K. Biobank. To compensate for the relative lack of old people in the Biobank, the researchers used the participants' parents age at death as a proxy as they looked for the influence of specific mutations on survival.
They found that in women over 70, the frequency of the ApoE4 gene linked to Alzheimer's dropped. This is consistent with lifespan data as women with one or two copies of the gene tend to die well before those without it. Researchers also saw a drop in the frequency of a mutation in the CHRNA3 gene associated with heavy smoking in men. This suggests that selection has purged similar variants from the population, even those that act later in life like the ApoE4 and CHRNA3 genes.
However, the researchers caution that the environment plays a role too. "A trait associated with a longer lifespan in one population today may no longer be helpful several generations from now or even in other modern day populations," said the study's lead author, Hakhamenesh Mostafavi, a graduate student at Columbia.
As more people agree to have their genomes sequenced and studied, researchers hope that information about how long they lived, and the number of kids and grandkids they had, can reveal further clues about how the human species is currently evolving.
Image: New research finds that the genetic variants linked to Alzheimer's disease and heavy smoking are less frequent in people with longer lifespans, suggesting that natural selection is weeding out these unfavorable variants in some populations. Image courtesy of the National Institutes of Health.