Humans almost became extinct about 1 million years ago. At that time the world’s population numbered only about 1,300 for more than 100,000 years.
One study says this near-extinction may have played a big role in the evolution of modern humans and their closest extinct relatives, the thick-browed Neanderthals and the mysterious Denisovans.
Previous studies have shown that modern humans originated around 300,000 years ago in Africa. With so few fossils from that time, there is still much uncertainty about how human lineages evolved before modern humans appeared.
To . about the period approaching modern human evolution, the scientists investigated the genomes of more than 3,150 present-day modern humans from 10 African and 40 non-African populations.
They developed a new analytical tool to infer the size of the groups that made up the ancestors of modern humans by looking at the diversity of genetic sequences seen in their offspring.
Genetic data shows that between 813 thousand and 930 thousand years ago, the ancestors of modern humans experienced a severe ‘bottleneck’, namely the loss of around 98.7% of their breeding population.
“Our ancestors experienced such a severe population stall over a very long time that they faced a high risk of extinction,” said study co-author Wangjie Hu of the Icahn School of Medicine at Mount Sinai, New York City, quoted by Live Science.
Researchers in the study published in the scientific journal Science estimate that the modern human breeding population numbered around 1,280 for around 117 thousand years.
“The estimated population size of our lineage ancestors is very small, and certainly would have brought them closer to extinction,” said Chris Stringer, a paleoanthropologist at London’s Natural History Museum who was not involved in the study.
Scientists note that this population decline coincided with severe cooling that resulted in the emergence of glaciers, lower sea surface temperatures, and possibly long droughts in Africa and Eurasia.
Scientists still don’t know how climate change will affect humans because fossils and human artefacts are relatively rare at this time, possibly because populations were so small.
Ancestors of Modern Humans
Previous studies have shown that the last common common ancestor of modern humans, the Neanderthals and the Denisovans, lived about 765,000 to 550,000 years ago, roughly the same time that the newly discovered population growth stall occurred.
This suggests that the near extinction of this species is potentially related to the evolution of the last common ancestors of modern humans, the Neanderthals and Denisovans.
“If this last common ancestor lived during or soon after the bottleneck, then the bottleneck may have played a role in splitting early human groups into modern humans, Neanderthals and Denisovans,” explains Stringer.
For example, Stringer continues, this may have divided humans into small, separate groups, and over time, the differences between these groups would have proven significant enough to divide the survivors into a distinct population, modern humans. , Neanderthals, and Denisovans.
Additionally, previous research suggests that around 900,000 to 740,000 years ago, two ancient chromosomes fused to form what is now known as chromosome 2 in modern humans.
Because this coincides with existing barriers, the new findings suggest that the near-extinction of humans may have had something to do with major changes in the human genome.
“Since Neanderthals and Denisovans shared this fusion with us, it must have occurred before our lineages separated from each other,” Stringer said.
“Future research may apply this new analysis technique to other genome data, such as Neanderthals and Denisovans. This may reveal whether they also experienced major obstacles,” he concluded.
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