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 suggests that our ancestors experienced an extreme population bottleneck around 900,000 years ago. This means that for over 100,000 years, only a thousand 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.
The Debate
Many question whether this was a near-extinction event or a mirage created by genetic inference limitations. The truth lies at the intersection of genomics, climate change, and the uncertainties of reconstructing ancient life.
The Evidence
The study analyzed genetic data from 3,000 individuals using a new statistical method called FitCoal. The results showed a dramatic population decline to around 1,280 individuals, a 98% drop, which persisted 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 dramatic climate change. Longer, colder glacial cycles disrupted ecosystems across Africa and Eurasia, devastating early human ancestors.
Implications
This prolonged environmental stress may explain the low population levels and slow rebound. The bottleneck could have reduced diversity, setting the stage for later evolutionary innovations. It also coincides with the loss of one pair of ancestral chromosomes, making genetic changes easier for small populations.
The Uncertainty
Critics argue that the signal could be a statistical artifact due to population structure and introgression. Fossil evidence is incomplete, so we can’t be 100% certain about the near-extinction event.
The Takeaway
The 2023 study presents a strong genetic case, but the reality remains uncertain. If true, it would mean our existence today is a product of extraordinary contingency, and our resilience is a result of small populations adapting and enduring.
