Evolution of Genetic Health Improvements in Humans Stall over Last Millennium
Had an arrow in his back not felled the legendary Iceman some 5,300 years ago, he would have likely dropped dead from a heart attack. Written in the DNA of his remains was a propensity for cardiovascular disease.
Heart problems were much more common in the genes of our ancient ancestors than in ours today, according to a new study by the Georgia Institute of Technology, which computationally compared genetic disease factors in modern humans with those of people through the millennia.
Overall, the news from the study is good. Evolution appears, through the ages, to have weeded out genetic influences that promote disease, while promulgating influences that protect from disease.
Charted data clearly illustrate a progressive improvement over the millennia in the genetic foundations of health, in nearly all diseases examined. Smaller shapes indicate better overall foundations. The dotted round line labeled 50% indicates average modern human disease allele occurrence. (Credit: Georgia Tech / LaChance, Berens, Cooper, Callahan)
But for us modern folks, there's also a hint of bad news. That generally healthy trend might have reversed in the last 500 to 1,000 years, meaning that, with the exception of cardiovascular ailments, disease risks found in our genes may be on the rise. For mental health, our genetic underpinnings looked especially worse than those of our ancient forebears.
Though the long-term positive trend looks very clear in the data, it's too early to tell if the initial impression of a shorter-term reversal will hold. Further research in this brand-new field could dismiss it.
"That could well happen," said principal investigator Joe Lachance, an assistant professor in Georgia Tech's School of Biological Sciences. "But it was still perplexing to see a good many of our ancestors' genomes looking considerably healthier than ours do. That wasn't really expected."
Lachance, former postdoctoral assistant Ali Berens, and undergraduate student Taylor Cooper published their results in the journal Human Biology . They hope that by better understanding our evolutionary history, researchers will someday be able to project future human populations' genomic health forward, as well as perhaps their medical needs.
Georgia Tech Assistant Professor Joe Lachance (l.) and undergraduate researcher Taylor Cooper (r.) performed the comparative genetic analysis with former Georgia Tech researcher Ali Berens (not shown). Credit: Georgia Tech / Christopher Moore
Dismal Distant Past
Despite what may be a striking, recent negative trend, through the millennia genetic risks to health clearly appear to have diminished, according to the study's main finding. "That was to be expected because larger populations are better able to purge disease-causing genetic variants," Lachance said.
The researchers scoured DNA records covering thousands of years of human remains along with those of our distant evolutionary cousins, such as Neanderthals, for genetic locations, or "loci," associated with common diseases. "We looked at heart disease, digestive problems, dental health, muscle disorders, psychiatric issues, and some other traits," Cooper said.
After determining that they could computationally compare 3,180 disease loci common to ancients and modern humans, the researchers checked for genetic variants, or "alleles," associated with the likelihood of those diseases, or associated with the protection from them. Nine millennia ago and before that, the genetic underpinnings of the diseases looked dismal.
"Humans way back then, and Neanderthals and Denisovans -- they're our distant evolutionary cousins -- they appear to have had a lot more alleles that promoted disease than we do," Lachance said. "The genetic risks for cardiovascular disease were particularly troubling in the past."
A young looking but sick and weak Neanderthal ( CC BY-NC-ND 2.0 )
Crumbling Health Genetics?
As millennia marched on, overall genetic health foundations got much better, the study's results showed. The frequency of alleles that promote disease dropped while protective alleles rose at a steady clip.
Then again, there's that nagging initial impression in the study's data that, for a few centuries now, things may have gone off track. "Our genetic risk was on a downward trend, but in the last 500 or 1,000 years, our lifestyles and environments changed," Lachance said.
This is speculation, but perhaps better food, shelter, clothing, and medicine have made humans less susceptible to disease alleles, so having them in our DNA is no longer as likely to kill us before we reproduce and pass them on.
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