Did Humans Nearly Go Extinct 900,000 Years Ago? A Biologist Explains
At some point in the deep past, humans may have come frighteningly close to disappearing altogether. Here’s what we know, according to research.
The Genetic Bottleneck Theory
A 2023 study published in Science (https://doi.org/10.1126/science.abq7487) suggests that our ancestors experienced an extreme population bottleneck around 900,000 years ago. This means that for over 100,000 years, only around 1,280 breeding individuals persisted. This would have been one of the most severe population crashes ever inferred for a large mammal, potentially erasing the human lineage before it truly began.
This theory has captured public imagination because it reframes our evolution. Most would assume it’s been a steady ascent, but this bottleneck suggests a narrow escape. However, it has sparked intense debate among scientists.
The Debate
Many geneticists argue that this bottleneck might be a mirage created by the limits of genetic inference. The truth lies at the intersection of genomics, climate change, and the uncertainties of reconstructing life from nearly a million years ago.
The Evidence
The study analyzed genetic data from over 3,000 present-day individuals using a new statistical method called FitCoal. The results showed a dramatic population decline of over 98% from earlier levels, persisting for over 100,000 years. This suggests humans were on the brink of extinction.
The Environmental Context
The bottleneck likely coincided with the Early-Middle Pleistocene Transition, a period of profound environmental upheaval. Dramatic changes in Earth’s climate system, particularly glacial cycles, disrupted ecosystems across Africa and Eurasia, making survival for early human ancestors extremely difficult.
Implications for Human Evolution
This bottleneck could have reduced genetic diversity, setting the stage for later evolutionary innovations. It also coincides with the estimated loss of one pair of ancestral chromosomes, a key development in human evolution.
The Uncertainty
Critics argue that the signal could be a statistical artifact, and fossil evidence doesn’t unequivocally suggest a near-extinction event. Even if the genetic signal is real, we can’t be 100% certain about its meaning.
Why This Matters
If humanity survived a near-extinction event, our existence today would be a product of extraordinary contingency. It would mean that our intelligence, culture, and technology are not inevitable but possibilities that survived a bottleneck few species escape.
Reframing Resilience
This theory also reframes our resilience as a species. Humans did not emerge because we were invincible but because small populations adapted, endured, and eventually expanded when conditions allowed.
A Humbling Perspective
Regardless of the exact reality, early human populations were far more fragile than once thought. This reminder should inspire humility in our understanding of human evolution, which wasn’t as smooth as we might believe.
