Humans Almost Went Extinct Nearly 1 Million Years Ago: How Did 1,300 Survivors Shape Humanity's Evolutionary Path?

Around 1 million years ago, humans faced near-extinction with a population at 1,300 for over 100,000 years. This event likely influenced the evolution of modern humans, Neanderthals, and Denisovans. While modern humans were thought to originate in Africa 300,000 years ago, limited fossils leave the earlier human lineage uncertain.

Ancient Human Population Experienced Bottleneck

An international team of scientists from China, Italy, and the United States utilized a novel method called FitCoal, based on modern human genomic sequences from 3,154 individuals, to fill a gap in the African/Eurasian fossil record.

By investigating the genomes of over 3,150 present-day modern humans from various populations, they created a new analytical tool to estimate the ancestral population size near the emergence of modern humans.

The genetic data revealed that approximately 813,000 to 930,000 years ago, the ancestors of modern humans underwent a significant bottleneck, losing nearly 98.7% of their breeding population, putting them at a high risk of extinction.

The study, titled "Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition" published in Science, sheds light on a critical period in human evolution, highlighting a prolonged and severe population bottleneck that played a crucial role in shaping the trajectory of our species.

The research team estimated that the breeding population of modern humans remained at approximately 1,280 individuals for approximately 117,000 years.

Chris Stringer, a paleoanthropologist at the Natural History Museum in London, who is not involved in the study, pointed out that the estimated population size for human's ancestral lineage was exceptionally small, placing them in close proximity to extinction.

Population Crash Coincided With Ancient Climate Change

The scientists observed that this population crash coincided with a period of significant cooling that led to the formation of glaciers, a decrease in ocean surface temperatures, and the possibility of prolonged droughts in Africa and Eurasia.

The impact of this climate change on humans remains uncertain due to the scarcity of human fossils and artifacts from this time, potentially resulting from the extremely low population size.

Previous research indicated that the last common ancestor shared by modern humans, Neanderthals, and Denisovans existed approximately 765,000 to 550,000 years ago, coinciding with the period of the newfound population bottleneck. This suggests a potential link between the near-eradication event and the evolution of this common ancestor.

If this last common ancestor lived during or shortly after the bottleneck, it might have contributed to the division of ancient human groups into modern humans, Neanderthals, and Denisovans.

For instance, the bottleneck could have led to the separation of humans into smaller isolated groups. Over time, the genetic differences that emerged within these isolated groups could have become substantial enough to result in the distinct populations we know today as modern humans, Neanderthals, and Denisovans.

The fusion of two ancient chromosomes around 900,000 to 740,000 years ago, forming what is now chromosome 2 in modern humans, coincided with the population bottleneck. This suggests a potential link between the near-eradication event and this significant genomic change, as Neanderthals and Denisovans also share this fusion with modern humans. Future research might use this analytical technique to investigate whether Neanderthals and Denisovans underwent similar population bottlenecks.

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