@science: Nearly a million years ago, humanity teetered on the edge of extinction. Genetic evidence reveals that between 813,000 and 930,000 years ago, our ancestors’ population collapsed to just about 1,280 breeding individuals. For more than 100,000 years, this fragile group carried the human lineage forward, their survival far from guaranteed. The cause appears tied to the mid-Pleistocene transition, when Earth’s climate grew harsher. Glacial cycles lengthened, sea temperatures dropped, and Africa and Eurasia endured extended droughts. With food scarce and ecosystems shifting, our ancestors faced conditions that nearly erased them from history. Scientists discovered the bottleneck using a new computational tool called FitCoal, which analyzed the genomes of over 3,000 people alive today. By tracing genetic variation backward in time, the team reconstructed population sizes and uncovered the staggering crash. About 98.7 percent of our genetic diversity was lost, and that scarcity still shapes human DNA today. This crisis may have sparked evolutionary change. Researchers suggest the bottleneck coincides with the rise of Homo heidelbergensis, a species considered a common ancestor of modern humans, Neanderthals, and Denisovans. Some even link it to the fusion of two ancestral chromosomes that created chromosome 2, a defining feature of our genome. The fossil record mirrors the mystery. Between 900,000 and 600,000 years ago, evidence of human activity is scarce, especially in Africa. Yet when conditions improved, perhaps with the harnessing of fire around 780,000 years ago, populations rebounded. Within a short span, humanity flourished once again, laying the foundation for our eventual global spread. What lingers is the lesson of fragility. At one point, our entire future rested in the survival of barely more than a thousand individuals. Without them, neither our species nor our history would exist. Source: 10.1126/science.abq7487

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Saturday 30 August 2025 08:00:13 GMT