Evidence that human evolution driven by major environmental pressures discovered

The genes of ancient humans might have changed substantially due to environmental pressures and change, say an international team of researchers.

A widely held belief related to human evolution is that our ancient ancestors’ ability to fashion tools, shelter, and use advanced communication skills may have helped to shield them from large environmental impacts such as changing climate, disease and exposure to other events affecting mortality.

But research led out of Australian Centre 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 frequency of these genes in human groups was masked by the exchange of DNA between people during reproduction.

Now, analyses of more than one thousand ancient genomes dating as far back as 45,000 years ago have found historic signals showing genetic adaptation was more common than previously thought.

The study of evolutionary events, says the study’s co-lead author Dr Yassine Souilmi, has increased substantially in recent years, as these are the points where human genetics take historic turns.

“Evolutionary events [are] exactly what shape our genetic diversity today,” Souilmi tells Cosmos.

“That’s what makes us vulnerable to certain diseases [and] resistant to others.

Dr yassine souilmi 2
Dr Yassine Souilmi / Credit: University of Adelaide

“Having a good understanding of evolution, we can have a better understanding of who we are.”

Previous research by the Centre has uncovered a range of evolutionary trends, from historic climate change causing the demise of ancestral lions and bears, to the first interactions between humans and coronaviruses 20,000 years ago.

And the broader field of research into ancient DNA has shed light on important moments in human history. Only recently did analyses of ancient genes uncover locations on the human genome associated with surviving Yersinia pestis – the bacterium that causes the bubonic plague.

Single events probably triggered selection

This study, published in Nature Ecology and Evolution, has similarly found environmental events might have been more influential on evolution among Eurasian groups.

Such events might lead to a point of natural selection. Take, for instance, the emergence of a pathogen. If such a disease could kill people, those who managed to survive and continue reproducing would pass down favourable traits to subsequent generations.

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

“It only cares about whether you’re procreating successfully… when it acts, it’s either killing a lot of people, [preventing] some people from reproducing successfully, or some people are just not finding mates because they have some sort of ailment that’s not allowing them to mate successfully, or might make them undesirable.

“What we’re finding is that the signal of natural selection we detected in this [research] was likely a single event, because the signal is clustered in time in a very early migration out of Africa.

“Not all of the [events] we detected occurred at the same time, but the bulk of them did.”

A mirror to the present

This ‘agnostic’ study did not seek to identify the external pressures leading to the selection events indicated in these ancient genes, but future research by the team will seek to uncover that information.

Studies like this, or those into specific pressures like the influence 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 the Earth’s climate, or the emergence of new pathogens, likely imposed selection pressures on ancient groups, whether through forcing shortages or changes to food supply or imposing physiological stressors.

“Very likely, it’s the environment, the temperature, the weather patterns, that would have somewhat impacted the dietary regime of our ancestors out of Africa, and pathogens would have driven this [genetic] adaptation, which has shaped our genetic diversity now,” Souilmi says.

“The direct lesson, socially, now, is that if we’re ever faced with events that are similar to that, we are not as immune to extreme episodes of adaptation where a lot of people might die, or be unable to reproduce.

“Unless we do something to counteract the environmental changes, or viruses, bacterial or other pandemics, it could be a bad thing.”

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