Around 900,000 years ago, humanity stood on the edge of extinction. A groundbreaking genomics study revealed that our ancestors dwindled to a mere 1,300 individuals, facing a critical bottleneck that nearly wiped us out. Concurrently, a significant human migration from Africa was taking place, a finding that aligns with the timing of this dramatic population decline. This migration and the population drop are believed to be connected to a major climatic shift known as the Mid-Pleistocene Transition, a time when Earth’s climate was in chaos, leading to the extinction of numerous species.
Tracing the journey of early humans from Africa into Europe and Asia is a complex task. The clues we have are few, mainly consisting of scattered bones and stone tools, which present dating challenges. However, the evidence points not to a single migration event but to multiple waves of early humans and their ancestors venturing into new lands.
Recent research has linked this human migration to the population bottleneck, with studies offering different timelines. One study, through a detailed examination of human genomes, pinpointed the bottleneck to about 900,000 years ago. Another study, focusing on archaeological sites in Eurasia, dated it to 1.1 million years ago. This discrepancy has led researchers to seek a more precise understanding of when and why this population decline occurred.
Researchers Giovanni Muttoni and Dennis Kent re-examined early hominid habitation sites across Eurasia, identifying a cluster of sites dating back to 900,000 years ago. They compared their findings with marine sediment records, which track climate changes through oxygen isotope ratios. These records, alongside the genomic data, suggest the bottleneck and migration occurred simultaneously.
During the Mid-Pleistocene Transition, global ocean levels fell, and Africa and Asia experienced severe droughts. This would have made living conditions in Africa extremely difficult, pushing early humans to migrate. The researchers propose that this migration was a direct response to the harsh climate, offering a means of survival.
This research does not imply that there were no previous migrations. Instead, it highlights that the significant bottleneck and subsequent migration of early Homo populations happened concurrently with the climatic upheaval 900,000 years ago. The researchers suggest that the spread of savannas and arid zones across Africa during this time forced early Homo populations to either adapt or migrate to avoid extinction.
Their findings, which contribute to our understanding of early human migration and its connection to climate change, have been published in the Proceedings of the National Academy of Sciences.