Climate change reduced ancient humans to mere 1,300 people some 900,000 years ago

Modern humanity's ancestors were on the brink of extinction some 900,000 years ago, reduced to a breeding population of barely 1,300 individuals due to climate change.

According to a study published in the Proceedings of the National Academy of Sciences, the population decline and mass migration of humans out of Africa have a connection to a common denominator, the Mid-Pleistocene Transition. Earth's climate change underwent a drastic turmoil, wiping out several species during this time.

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It's hard to reconstruct the movement of early humans into and across Europe and Asia from Africa. The shreds of evidence (bones and stone artefacts) suggest that it wasn't one event but multiple waves.

Two recent studies have found that human migration caused a population bottleneck through different types of analysis. While one studied early archaeological sites in Eurasia and dated the bottleneck to 1.1 million years ago, the other was a close analysis of the human genome that found a population bottleneck that caused a loss of genetic diversity some 900,000 years ago.

Geologists Giovanni Muttoni of the University of Milan and Dennis Kent of Columbia University tried to narrow down the bottleneck's timing. They re-evaluated records of sites of early hominid habitation across Eurasia. They discovered a group of sites reliably dated to 900,000 years ago.

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According to the genomic data and the dating of the hominid sites, the population bottleneck and the migration were concurrent. Global ocean levels dropped during the mid-Pleistocene transition, causing Africa and Asia to dry out.

However, the falling sea levels opened up land routes in Eurasia. According to the researchers' model, the hominids would've skedaddled. The researchers carefully note that hominids had migrated previously. But around 900,000 years ago, there was a population bottleneck in the ancestor of modern Homo sapiens due to a climate upheaval that was occurring at the same time as their migration.

"We suggest that the enhanced aridity during marine isotope stage 22 that caused the spread of savanna and arid zones across much of continental Africa pushed early Homo populations in Africa to adapt or migrate to avoid extinction," they write in their paper. "Rapid migration in response to a severe climate trigger and concomitant means to escape is what can account for the … migration out-of-Africa at 0.9 million years ago and contribute to the modern genomic evidence in modern African populations of the bottleneck," they added.

(With inputs from agencies)