Humans may be just as vulnerable to the effects of environmental change as other animals, according to new research analyzing the genetic data of more than 1,000 people who have lived across Europe and Asia over the past 45,000 years.
group leader Yassin Swelmi, a genomics and bioinformatics scientist at the Australian Center for Ancient DNA, the University of Adelaide found; Christian Huber, assistant professor of biology, Penn State, and Ray Tobler, postdoctoral fellow, Australian National University, traced more than 50 “difficult scans” in which a rare genetic variant quickly swept across the population – likely after a change in the circumstances in which those died. who lack the variable. The most striking sweep of the early farmers in Anatolia occurred in a genetic region linked to the immune system called MHC-III.
Difficult scans have often been seen in other species, but so far there have been few signs of them in humans. The effects of the difficult raids were masked by the frequent mixing of the population over the past eight thousand years.
The results show that our famous ability as humans to adapt our behavior and develop new tools and technologies was not always enough to survive when times got tough.
How does natural selection work
Modern humans live in a large variety of natural environments, from the Arctic to the rainforests of the rainforests.
Unlike most animals, humans can rely on cultural innovations – such as fire and clothing – to overcome challenges in these environments.
However, these innovations may not always be sufficient to deal with new environmental conditions. This is when genetic variation between individuals plays a role.
They make individuals with genetic variations more willing to deal with new conditions, and they tend to leave more offspring. As a result, these beneficial variants become more common in future generations.
Charles Darwin called the process of genetic adaptation “natural selection” nearly 200 years ago.
How do people adapt?
Using statistical tools to look for evidence of challenging scans, researchers have found ample evidence of past adaptive events in many animals and plants, but little in the human genome. More specifically, difficult scans are conspicuously rare in humans.
As a result, some have speculated that genetic adaptation in humans is rare, possibly because cultural innovations have rendered it largely unnecessary. Others have suggested that the selection occurred across several rather beneficial genetic variants, resulting in subtle, hard-to-detect signals.
Nearly 40 years ago, new techniques were developed to extract trace amounts of DNA from archaeological skeletal remains. This made it possible to study the genomes of ancient populations and changed our view of how ancient human groups and civilizations were related to one another.
Ancient DNA research revealed that over the past 10,000 years, the mixing of genetically disparate populations of Eurasia has been particularly frequent.
We thought these events might have erased historical scans from the modern human genome – but ancient genomes that preceded these tangled events may still retain traces of the signals.
About 10,000 years ago, after the end of the last Ice Age, there was much more genetic diversity among the hunter-gatherers living in Europe than there is among the humans living there today.
Indeed, the genetic differences between ancient European hunter-gatherer groups were as great as the differences now observed between modern populations in Western Europe and East Asia.
This intense genetic differentiation has collapsed over the past 8,000 years due to numerous migrations and admixture events, making modern Europeans more genetically homogeneous.
Difficult surveys in human history
In the new paper, published in Nature Ecology & Evolution, researchers revisit this question by scanning more than a thousand ancient human genomes obtained from across Eurasia.
They said: Could the relatively recent admixture events obscure the historical selective scans, so they were invisible in the modern human genome?
To test this idea, they first ran some computer simulations based on estimates of genetic admixture from studying the genomes of ancient Eurasia. The simulation results suggested that ancient selection signals could indeed be severely attenuated in the modern genome.
Next, they collected and analyzed genetic information from more than 1,000 ancient human remains, with the oldest sample being around 45,000 years old.
They compared the signals of selection in the ancient genome to those in the modern genome. Older data contained many more challenging survey signals than recent samples. Recent scans have been particularly vulnerable to erasure, due to their being rare or absent in at least one of the confounding groups.
The findings confirm that challenging scans were indeed part of the repertoire of human genetic adaptation. This suggests that we may not be completely different from other animal species after all.
The genetic basis of adaptation
Genetic evidence of historical admixture events between different populations is increasing. This is not only in humans but also in other species, suggesting that such admixture may be reasonably common in nature.
If these admixture events are widespread, our study suggests that challenging sweeps may also be more common than we currently think. In general, we may have a biased view of how species are genetically adapted to environmental stresses.
To fully understand how adaptation works at the genetic level, we will need to develop new statistical methods to decouple signals from challenging scans and other selected events.