Natural selection appears to still be at work, improving our ability to survive, according to a large-scale study of genetic data.
The study of the genomes of 210,000 people in the US and UK 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.
The study in the journal PLOS Biology by researchers at Columbia University and the University of Cambridge found that sets of mutations linked to particular physiological states, such as early puberty and asthma, also appear less often in people who live longer.
“It’s a subtle signal, but we find genetic evidence that natural selection is happening in modern human populations,” says coauthor Joseph Pickrell.
In women over 70, researchers saw a drop in the frequency of the gene linked to Alzheimer’s, consistent with earlier research showing that women with one or two copies of the gene tend to die well before those without it.
Researchers saw a similar drop, starting in middle age, in the frequency of a mutation in the gene associated with heavy smoking in men.
The researchers were surprised to find just two common mutations across the entire human genome that heavily influence survival.
The high power of their analysis should have detected other variant. This suggests that selection has purged similar variants from the population, even those that act later in life.
“It may be that men who don’t carry these harmful mutations can have more children, or that men and women who live longer can help with their grandchildren, improving their chance of survival,” says study co-author Molly Przeworski.
They also found that a predisposition for high cholesterol and LDL “bad” cholesterol, high body mass index, and heart disease was linked to shorter life spans.
To a lesser extent, a predisposition for asthma was also linked to earlier death.
They also found that those genetically predisposed to delayed puberty and child-bearing lived longer. A one-year puberty delay lowered the death rate by 3% to 4% in both men and women. A one-year childbearing delay lowered the death rate by 6% in women.
Researchers take the results as evidence that genetic variants influencing fertility are evolving in some populations in the US and Britian.
But they caution that environment plays a role as well, meaning that traits that are desirable now may not be in other populations or in the future.
“The environment is constantly changing,” says the study’s lead author, Hakhamenesh Mostafavi. “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.”
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