"Debating the Near-Extinction Theory: Did 1,280 Ancestors Nearly Determine Humanity's Fate 900,000 Years Ago?"

 

"Debating the Near-Extinction Theory: Did 1,280 Ancestors Nearly Determine Humanity's Fate 900,000 Years Ago?"

Could the fate of our planet's eight billion current inhabitants be traced back to the resilience of just 1,280 human ancestors who nearly faced extinction nearly 900,000 years ago? A recent study utilizing genetic analysis modeling suggests precisely this, positing that our ancestors hovered on the precipice of annihilation for approximately 120,000 years.

However, the study's claims have faced criticism from scientists not involved in the research. One expert even asserted that there was "pretty much unanimous" disagreement among population geneticists regarding the study's persuasiveness. While none denied the possibility of human ancestors nearing extinction, doubts were raised about the precision of the study, given the daunting challenge of estimating population changes from such a distant era. Furthermore, similar methodologies had not previously detected such a significant population decline.

Extracting DNA from fossils of human relatives dating back more than a few hundred thousand years has always been incredibly challenging. However, advancements in genome sequencing now enable scientists to examine genetic mutations in modern humans and employ backward-facing computer models to infer historical population changes.

The study, published in the journal Science, centered on the genomes of over 3,150 contemporary humans. A team led by Chinese researchers developed a model to analyze the data, concluding that the population of breeding human ancestors dwindled to around 1,280 individuals approximately 930,000 years ago.

According to co-author Haipeng Li of the Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences, "About 98.7 percent of human ancestors were lost" at the onset of this bottleneck. He noted that "our ancestors almost went extinct and had to work together to survive."

The bottleneck, possibly triggered by a period of global cooling, persisted until about 813,000 years ago, as suggested by the study. Subsequently, there was a population surge, likely influenced by a warming climate and the mastery of fire.

The study's authors speculated that inbreeding during the bottleneck could account for the comparatively lower genetic diversity in humans compared to many other species. Additionally, this population squeeze might have played a role in the distinct evolution of Neanderthals, Denisovans, and modern humans, all of whom are believed to have diverged from a common ancestor around the same period.

However, some archaeologists have pointed to fossil findings from Kenya, Ethiopia, Europe, and China from that era, suggesting a wider distribution of human ancestors than the bottleneck scenario would suggest.

In response, the study's authors argued that hominins living in Eurasia and East Asia at that time might not have contributed to the ancestry of modern humans, emphasizing that the ancient, small population represents the ancestors of all contemporary humans.

The study received considerable skepticism from experts in the field. Stephan Schiffels of Germany's Max Planck Institute for Evolutionary Anthropology expressed doubts about the precision of the researchers' calculations, emphasizing the inherent statistical uncertainties in such analyses.

Schiffels also noted that the data used in the study had been available for years, and previous methods employing this data hadn't identified a near-extinction event. Despite the authors simulating the bottleneck using previous models, experts remained unconvinced, as the models should have detected the bottleneck initially.

Aylwyn Scally, a researcher in human evolutionary genetics at Cambridge University, voiced the prevailing sentiment among population geneticists, stating that while our ancestors may have faced near-extinction at some point, the ability of modern genomic data to definitively confirm such an event was "very weak."