Chronic illnesses such as asthma and Alzheimer’s disease are seemingly being wiped out from human genes thanks to natural selection, as part of human evolution.
According to a ground-breaking study, gene variations associated with asthma, Alzheimer’s and high cholesterol have noticeably declined in just two generations. Scientists say this effectively proves that Darwinian evolution not only exists, but is still taking place.
The findings, which follow an analysis of the genetic blueprints of 150,000 Britons and 60,000 Americans carried out by researchers from Columbia and Cambridge University, suggest the diseases could be “weeded out” of the human species in a few thousand years.
"It's a subtle signal, but we find genetic evidence that natural selection is happening in modern human populations," said Joseph Pickrell, an evolutionary geneticist at Columbia University and one of the study’s authors, the Telegraph reported.
Scientists taking part in the study, published in the PLOS Biology journal, believe men without Alzheimer’s could be able to have more children, while both men and women with Alzheimer’s tend to be less capable of looking after their grandchildren.
These factors affect survival while also limiting the propagation of the genes.
“For example, if men with ApoE4 have 0.1% fewer children on average than men without them, this would be enough for these variants to be removed quickly by natural selection,” said lead researcher Hakhamenesh Mostafavi.
According to technology news website Alpha, study co-author Molly Przeworski, an evolutionary biologist at Columbia, added: "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.”
Meanwhile, variations associated with good health conditions are more likely to be passed on and are, as a result, increasingly present in the human gene pool.
The study also found that those who are predisposed to delayed puberty are likely to live longer.
A one-year delayed puberty slashed the death rate by three to four percent in both men and women.
Delayed child-bearing also seemed to lengthen women’s lives, with a one-year delay accounting for the death rate being slashed by six percent.
"The environment is constantly changing," Mostafavi remarked.
"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."