Ancient human population dwindled to 1,300 due to climate change 900,000 years ago

Around 900,000 years ago, the ancestors of modern humans nearly faced extinction, with their numbers dwindling to approximately 1,300 breeding individuals. This drastic reduction was largely attributed to climate change, as highlighted in a study published in the Proceedings of the National Academy of Sciences. The study links the severe decline in human population and the subsequent exodus from Africa to a period known as the Mid-Pleistocene Transition, marked by significant climate upheaval and the extinction of numerous species.

Tracing the journey of early humans from Africa into Europe and Asia reveals a complex pattern of migration involving multiple waves, as inferred from archaeological remnants like bones and stone tools.

Recent research efforts have pinpointed a significant reduction in human population, termed a “population bottleneck,” through diverse analytical approaches. One analysis focused on early archaeological sites in Eurasia, dating the bottleneck to about 1.1 million years ago, whereas genomic analysis identified a reduction in genetic diversity occurring roughly 900,000 years ago.

Geologists Giovanni Muttoni from the University of Milan and Dennis Kent from Columbia University aimed to pinpoint the timing of this bottleneck more accurately by examining records from early hominid habitation sites across Eurasia. They identified a cluster of sites dating back to 900,000 years ago.

The data from these sites, along with genomic evidence, suggest that this population bottleneck and the migration events happened simultaneously. The mid-Pleistocene transition led to significant drops in global ocean levels, drying out large parts of Africa and Asia but also revealing land bridges in Eurasia that facilitated migration.

Muttoni and Kent propose that the harsher aridity during this period expanded savanna and arid zones throughout Africa, forcing early Homo populations to either adapt or migrate to evade extinction. This quick migration in response to severe climate changes, along with new pathways opening up due to lower sea levels, explains the movement out of Africa around 900,000 years ago. This scenario aligns with modern genetic evidence of a bottleneck in the genomes of contemporary African populations, indicating a critical juncture in human evolution triggered by climatic shifts.