Nearly a million years ago, a cataclysmic event nearly wiped out mankind’s ancestors.
Currently, a species is considered critically endangered if its population is less than 1000 individuals. Genomic data from 3,154 modern humans suggest that the population declined from around 100,000 to just 1,280 breeding individuals around 900,000 years ago. This is a staggering 98.7% population decline that lasted 117,000 years and could have led to human extinction.
The fact that we are here today and that we are so numerous is proof that this was not the case. However, according to a team led by geneticists Haipeng Li of the Chinese Academy of Sciences and Yi-Hsuan Pan of East China Normal University, the results would reveal a curious gap in the Pleistocene human fossil record and explain the famous hole in the fossil record, the creationists sometimes use as an argument.
“The gap in the fossil records of Africa and Eurasia can be chronologically explained by this bottleneck in the early Stone Age,” says anthropologist Giorgio Manzi of the Sapienza University in Rome, Italy. “It corresponds to the proposed period of significant loss of fossil evidence.”
Population bottlenecks, since the number of individuals in a group is known to decrease significantly, are not uncommon. When a species is destroyed by an event such as war, famine, or a climate crisis, the resulting decline in genetic diversity can be tracked in the offspring of the survivors. So we know that there was also a shortage of human population in the northern hemisphere much more recently, about 7000 years ago.
The further back in time you want to look, the harder it is to extract a meaningful signal. In this latest analysis, the research team developed a new method called the Fast Coalescing Process in Infinitesimal Time (FitCoal) to circumvent the accumulation of numerical error that often accompanies attempts to decipher these past phenomena.
Researchers used FitCoal to analyze genome data from 3,154 people around the world, from 10 African and 40 non-African populations, to examine how genetic lineages diverged over time. Their results showed a significant population bottleneck from around 930,000 to 813,000 years ago, resulting in a loss of up to 65.85% of current genetic diversity.
As for what caused the bottleneck, we can never be 100% sure what all contributed to it, but there was one important event back then that may have played a role: the transition to the Middle Pleistocene, during which the Earth’s ice age broke out in The Cycles have changed drastically.
Climate turbulence may have created unfavorable conditions for the then struggling human population, leading to famine and conflict that further reduced populations.
“The novel finding opens a new field in human evolution because it raises many questions,” says Pan, “e.g. B. where these individuals lived, how they survived catastrophic climate changes, and whether natural selection during the bottleneck accelerated the course of human evolution.” “human brain”.
The bottleneck appears to have contributed to another interesting feature of the human genome: the fusion of two chromosomes to form chromosome 2. Humans have 23 pairs of chromosomes; all other hominids alive today—including the great apes—have 24. The formation of chromosome 2 appears to have been a speciation event that propelled humans down a different evolutionary path.
“These findings are just the beginning,” says Li. “Future goals with this knowledge aim to paint a more complete picture of human evolution during this transition period from early to middle Pleistocene, which in turn will further unravel the mystery of early human ancestry and evolution.” will air.”
REFERENCE
Are our ancestors almost extinct?
Photo: flowcomm for Flickr