Early human ancestors went through a prolonged period of very low population of only about 1,000 individuals on the planet about 900,000 years ago, threatening the fate of humanity as we know it today.
Scientists, including those from the Chinese Academy of Sciences, say this plunge in human ancestral population was likely due to drastic climate change around this time, including glaciation events causing changes in temperatures, severe droughts, and loss of other species that were potentially used as food sources.
In the study, published on Thursday in the journal Science, archaeologists attempted to explain a gap in the African/Eurasian fossil record by analysing modern-day human genomic sequences from 3,154 individuals.
The analysis revealed that early human ancestors went through a prolonged, severe bottleneck during which about 1,280 breeding individuals were able to sustain a population for about 117,000 years.
Researchers found evidence that during this period early human ancestors experienced extreme loss of life and therefore, loss of genetic diversity.
They say an estimated 65 per cent of genetic diversity may have been lost due to this bottleneck with a prolonged period of minimal numbers of breeding individuals in the early to middle Pleistocene era.
However, they suspect this bottleneck may have contributed to a speciation event where two ancestral chromosomes may have converged to form what is currently known as chromosome 2 in modern humans.
This may have led to the rise of the species that was likely the last common ancestor for the Denisovans, Neanderthals, and modern humans (Homo sapiens), scientists say.
The bottleneck theory, however, needs to be tested against the archaeological and fossil human evidence, they added.
Though the new study has led to some startling findings, researchers say it has also raised more questions.
Now that the study has revealed a likely ancestral struggle about 930,000 and 813,000 years ago, researchers hope to continue digging to find how such a small population persisted in assumably tricky and dangerous conditions.
“The novel finding opens a new field in human evolution because it evokes many questions, such as the places where these individuals lived, how they overcame the catastrophic climate changes, and whether natural selection during the bottleneck has accelerated the evolution of human brain,” study co-author Yi-Hsuan Pan said.
Scientists suspect the control of fire, as well as the climate shifting to be more hospitable for human life, may have contributed to a later period of rapid population increase around 813,000 years ago.
“These findings are just the start. Future goals with this knowledge aim to paint a more complete picture of human evolution during this Early to Middle Pleistocene transition period, which will in turn continue to unravel the mystery that is early human ancestry and evolution,” LI Haipeng, another author of the study, said.