Genetic Study Suggests Human Population Once Dropped to 1,280 Breeding Adults

The world's human population has surpassed 8 billion as of 2023. Researchers have conducted a genetic analysis suggesting a historical bottleneck where the effective human population size fell to about 1,280 breeding adults. This event is estimated to have occurred between 930,000 and 813,000 years ago, based on genomic data from modern humans.

The study, published in the journal Science on August 31, 2023, analyzed the genomes of 3,154 individuals from diverse populations worldwide. Scientists identified reduced genetic diversity in certain chromosomal regions, consistent with a severe population decline.

Such a bottleneck would have left a lasting signature in human DNA, detectable through statistical modeling of mutation rates and recombination patterns.

The research team, led by Haipeng Li from the Chinese Academy of Sciences, used advanced computational methods to simulate population scenarios.

They found that a decline to 1,280 breeding individuals aligns with observed patterns of genetic variation. This number represents the effective population size, meaning the number of individuals contributing to the gene pool, rather than the total census population, which could have been larger but included non-breeding members.

The bottleneck is thought to have coincided with a period of extreme climate change during the Mid-Pleistocene, including megadroughts and glacial conditions in Africa, where early humans likely originated.

Fossil records from this era show evidence of environmental stress, such as reduced vegetation and megafauna extinctions. The study proposes that these conditions, possibly lasting for 117,000 years, drastically reduced available resources and led to high mortality rates among early human groups.

This population minimum may have influenced human evolution by increasing the effects of genetic drift and inbreeding.

The analysis detected reduced diversity on the X chromosome, suggesting differential survival rates between males and females. Recovery from the bottleneck likely involved migration and adaptation to changing environments, shaping the genetic diversity seen in modern populations.

The findings build on previous research identifying other bottlenecks, such as the one around 70,000 years ago linked to the Toba supervolcano eruption.

However, this earlier event appears more severe in scale. Further studies could refine the timeline and explore archaeological evidence to corroborate the genetic data. Experts note that while the genetic evidence is compelling, direct fossil confirmation remains limited for this period.

Ongoing genomic sequencing from ancient remains may provide additional insights. The study underscores the vulnerability of early human populations to environmental pressures.