Bottleneck in human evolution explained using novel genomic analysis technique

New Delhi: A novel genomic analysis technique helped reveal a severe bottleneck in the growth of human population that almost wiped out the chance for humanity as it exists today, scientists report in a study published in the journal Science.

The study findings indicated that early human ancestors went through a prolonged, severe bottleneck in which approximately 1,280 breeding individuals were able to sustain a population for about 117,000 years, the research team from China, Italy and the US said.

They were able to accurately determine demographic inferences by using modern-day human genomic sequences from 3,154 individuals using a method called FitCoal, or fast infinitesimal time coalescent process.

FitCoal helped the researchers calculate the likelihood for present-day genome sequences found that early human ancestors experienced extreme loss of life and therefore, loss of genetic diversity.

"The gap in the African and Eurasian fossil records can be explained by this bottleneck in the Early Stone Age as chronologically. It coincides with this proposed time period of significant loss of fossil evidence," said senior author Giorgio Manzi, an anthropologist at Sapienza University of Rome.

Reasons suggested for this downturn in human ancestral population are mostly climatic: glaciation events around this time lead to changes in temperatures, severe droughts, and loss of other species, potentially used as food sources for ancestral humans.

An estimated 65.85 per cent of current genetic diversity may have been lost due to this bottleneck in the early to middle Pleistocene era (from two million to 11 thousand years ago), and the prolonged period of minimal numbers of breeding individuals threatened humanity as we know it today, the researchers said in their study.

However, this bottleneck seems to 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, they said.

With this information, the last common ancestor has potentially been uncovered for the Denisovans, Neanderthals, and modern humans (Homo sapiens), they said.

"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," said senior author Yi-Hsuan Pan, an evolutionary and functional genomics at East China Normal University (ECNU), China.

Now that there is reason to believe an ancestral struggle occurred between 930,000 and 813,000 years ago, researchers can continue digging to find answers to these questions and reveal how such a small population persisted in assumably tricky and dangerous conditions, the study said.