Our new research shows that humans are just as vulnerable to environmental change as other animals.
We found traces of more than 50 "hard sweeps" in which a rare genetic variant quickly swept through a population, most likely after a change in conditions in which those without the variant died out. There was a sweep among early Anatolian farming people in a genetic region associated with the immune system.
There have been hard sweeps in other species, but until now they have not been found in humans. Over the past 8,000 years, the hard sweeps have been hidden.
Humans' ability to adapt our behavior and develop new tools and techniques has not always been enough to survive when times are tough.
Modern humans live in a lot of different environments.
Humans can use cultural innovations, such as fire and clothing, to overcome the challenges they face.
These innovations may not have been enough to cope with the changing environment. Genetics come into play at this time.
People with genetic variations that make them better equipped to deal with new conditions tend to leave more children. Future generations will see these beneficial variant more often.
Charles Darwin called this process of genetic adaptation natural selection.
Researchers have found plenty of evidence for adaptive events in animals and plants, but not in humans. Hard sweeps are not very common in humans.
Genetic adaptation in humans is thought to be rare because of cultural innovations. It has been suggested that selection has occurred across a number of genes.
40 years ago, new technologies to extract tiny amounts of DNA were developed. The ability to study the genomes of ancient populations has made it possible to see how ancient human groups and civilizations are related to each other.
Intermixing between genetically different populations has been common over the past 10,000 years.
We thought the sweep signals from modern human genomes might have been erased by these events.
After the end of the last ice age, there was a lot of genetic variation among hunter-gatherers in Europe.
The genetic differences between groups of ancient European hunter-gatherers were as large as they are today.
Modern Europeans are much more genetically homogeneity due to several migrations and mixing events.
In our new research, we scanned more than a thousand ancient human genomes from all over the world.
We wondered if mixing events masked historical sweeps, so they were not visible in modern human genomes.
We ran computer simulations based on estimates of genetic mixing from studies. Simulation results suggested ancient selection signals could be weakened.
The oldest sample of ancient human remains was around 50,000 years old.
We looked at the selection signals from ancient and modern genomes. There were more hard sweep signals in the ancient data. The recent sweeps were rare or absent in at least one of the mixing populations.
Hard sweeps were part of the human genetic adaptation. We might not be so different from other animals after all.
There is growing genetic evidence for mixing events. It is possible that such mixing is common in nature.
Our study shows that hard sweeps may have been more common than we think. We might have a biased view of how species have adapted to the environment.
New statistical methods will need to be developed to disentangle signals of hard sweeps and other selection events in order to understand how adaptation works at a genetic level.
The Australian Centre for Ancient DNA is headed by a group of people.
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