Evidence has been discovered that human evolution is driven by major environmental pressures

The genes of ancient humans may have changed substantially due to environmental pressures and changes, says an international team of researchers.

A widely held belief related to human evolution is that our ancient ancestors’ ability to form tools, protect and use advanced communication skills may have helped protect them from major environmental impacts such as climate change, disease and the exposure to other events affecting mortality.

However, research carried out by the Australian Center for Ancient DNA at the University of Adelaide suggests that beneficial genes may have played a more important role in preserving our ancestors.

Until now, the sudden increase in the frequency of these genes in human groups was masked by the exchange of DNA between people during reproduction.

Now, analyzes of more than a thousand ancient genomes dating back 45,000 years have found historical signals that show genetic adaptation was more common than previously thought.

The study of evolutionary events, says study co-leader Dr Yassine Souilmi, has grown significantly in recent years, as these are the points where human genetics take historic turns.

“Evolutionary events [are] what exactly shapes our genetic diversity today,” says Souilmi Universe.

“This is what makes us vulnerable to certain diseases [and] resistant to others.

Dr Yassine Souilmi / Credit: University of Adelaide

“By having a good understanding of evolution, we can better understand who we are.”

Previous research by the Center has revealed a number of evolutionary trends, from historical climate change that caused the death of ancestral lions and bears, to the first interactions between humans and coronaviruses 20,000 years ago.

And the broader field of ancient DNA research has shed light on important moments in human history. Only recently have analyzes of ancient genes revealed sites in the human genome associated with survival Yersinia pestis – the bacterium that causes bubonic plague.

Single events probably triggered selection

This study, published in Nature Ecology and Evolutionhas similarly found environmental events may have had a greater influence on evolution among Eurasian groups.

Such events may lead to a point of natural selection. Take, for example, the emergence of a pathogen. If such a disease could kill people, those who managed to survive and continue to reproduce would pass on favorable traits to future generations.

“Natural selection acts on two different mechanisms,” says Souilmi.

“It only cares about whether it reproduces successfully… when it acts, whether it kills a lot of people, [preventing] Some people breed successfully, or some people just don’t find mates because they have some kind of condition that prevents them from mating successfully or can make them undesirable.

“What we find is that the signal of natural selection we detected in it [research] it was likely a single event because the signal is clustered in time to a very early migration out of Africa.

“Not all of them [events] we detected that they happened at the same time, but most of them happened.”

A mirror to the present

This “agnostic” study did not seek to identify the external pressures driving the selection events indicated in these ancient genes, but future research by the team will seek to uncover this information.

Studies like this, or those on specific stressors like the effect of the Black Death or coronaviruses on humans, show the impact of environmental change on our genetics.

Souilmi says this is both insightful and cautionary, as environmental change in the present could be studied by humans in the future.

He speculates that changes in Earth’s climate, or the emergence of new pathogens, likely imposed selection pressures on ancient groups, either through forced shortages or changes in food supply or by imposing physiological stressors.

“Very likely, it’s the environment, the temperature, the weather, that would have somehow affected the nutritional regime of our ancestors from Africa and the pathogens would have driven it [genetic] adaptation, which has shaped our genetic diversity now,” says Souilmi.

“The immediate lesson, socially, now, is that if we’re ever faced with events like this, we’re not as immune to extreme adaptation episodes where lots of people might die or be unable to reproduce.

“If we don’t do something about environmental changes or viruses, bacteria or other pandemics, it could be bad.”

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