An ‘Ancestral Bottleneck’ Took Out Nearly 99 Percent of The Human Population 800,000 Years Ago

A collaborative effort between researchers from the U.S., Italy, and China might have solved a longstanding mystery in the fossil records of Africa and Eurasia.

A study unveiled on August 31 in the Science journal posits that a dramatic decline occurred in the population of our forebears approximately 800,000 to 900,000 years in the past.

The team’s model suggests only about 1,280 reproductive individuals remained during this shift from the early to middle Pleistocene era. The research indicates a staggering 98.7% reduction in the early human population, initiating a genetic bottleneck that persisted for around 117,000 years.

The Late Pleistocene saw the migration of modern humans beyond Africa, the dwindling of species like the Neanderthals, and the initial human footprints in regions like Australia and the Americas. This period is predominantly characterized by colossal ice sheets and glaciers that redefined many of the globe’s existing terrains.

The scientists employed an innovative technique, named the fast infinitesimal time coalescent process (FitCoal), to extract ancient population data using the genomic sequences from 3,154 contemporary humans.

Through FitCoal, the researchers reconstructed the ancient decline and consequent genetic diversity loss using genomic data from 10 African and 40 non-African communities.

Several potential factors, predominantly climatic shifts, are believed to have triggered this decline. Fluctuating temperatures, prolonged droughts, and a potential scarcity of sustenance due to the extinction of creatures like mammoths, mastodons, and giant sloths might have contributed.

The study suggests that this bottleneck might have caused a loss of nearly 65.85% of the existing genetic diversity, marking an extended phase of minimal human numbers capable of reproducing, posing a significant threat to the human lineage.

Nevertheless, this population squeeze might have also spurred a speciation occurrence, a process where a single lineage bifurcates into two or more distinct species. In this context, two ancestral chromosomes may have amalgamated to produce modern humans’ chromosome 2.

This chromosome, encompassing roughly 243 million DNA base pairs, is the second largest in humans. This discovery enabled the researchers to identify a probable last shared progenitor for Denisovans, Neanderthals, and Homo sapiens.

Prospective research aims to unravel how such a constrained population managed to survive amidst harsh climatic challenges. Mastery over fire and a climate growing increasingly favorable for human habitation might have spurred the swift upsurge in human numbers around 813,000 years ago.