For years, scientists have been intrigued by the gap in the African and Eurasian fossil records compared to modern humans. However, a new study published in the journal Science seems set to reshape our understanding of early human history thanks to a new method that has provided tantalizing insights into a chapter of human history that had remained in the shadows.
Humans nearly went extinct about 900,000 years ago.Midjourney/Sarah Romero
Did humans really go extinct?
Using a state-of-the-art technique called FitCoal (infinitesimal time rapid coalescing process) and the genomic sequences of modern humans, researchers at East China Normal University developed a model that could look at modern gene lineages and use them to estimate earlier population size.. They used their model to analyze the DNA of 3,154 modern humans. of African and non-African populations, discovering that early humans nearly went extinct 900,000 years agowhen the population of our ancestors was reduced to only 1,280 individuals.
It was an amazing find. Our early human ancestors experienced a staggering bottleneck event at barely a thousand reproducers to carry the torch for humanity. for an astonishing 117,000 years. (Demographic bottlenecks, as significant reductions in the number of a group are known, are not uncommon.)
Shown on the right is the African hominin fossil gap and the estimated time period of the chromosome fusion.Science
What could have caused this debacle?
Scientists believe that an extreme weather event could have caused the bottleneck that nearly wiped out our ancestral line. Glaciation events during this period caused temperature changes and severe droughts. “The figures that emerge from our study correspond to those of species that are currently at risk of extinction”said Professor Giorgio Manzi, an anthropologist at the Sapienza University of Rome and lead author of the research.
Their results showed a significant population bottleneck from about 930,000 to 813,000 years ago.which meant a current loss of genetic diversity of up to 65.85 percent. This dramatic loss speaks volumes about the perseverance of our early human ancestors.
Curiously, this genetic bottleneck seems to have sparked a dramatic fight for survival, which could have played a crucial role in the formation of modern human chromosomes. Chromosome 2. Humans have 23 pairs of chromosomes; all other hominids alive today, including the great apes, have 24. The formation of chromosome 2 seems to be the engine that started a different evolutionary path.
“The novel finding opens up a new field in human evolution because it evokes many questions,” explained lead author Yi-Hsuan Pan, an expert in evolutionary and functional genomics at East China Normal University (ECNU). “For example, where did these individuals live, how did they overcome the catastrophic climate changes and whether natural selection during the bottleneck accelerated the evolution of the human brain,” the researchers wonder.
The fossil record from that time is scant.
The decline of these ancestors appears to coincide with significant changes in global climate that turned ice ages into long-term events, a decline in sea surface temperatures, and a possible long dry spell in Africa and Eurasia.
“These findings are just the beginning. Future goals with this knowledge aim to paint a more complete picture of human evolution during this transition period from the early to middle Pleistocene, which in turn will continue to unravel the mystery of early human ancestry and evolution,” says LI Haipeng, theoretical population geneticist and computational biologist at the Shanghai Institute of Nutrition and Health of the Chinese Academy of Sciences.
It seems that each answer raises new questions, but each time we get closer to completing the pages of the book of our ancient human lineage.
References:
- Wangjie Hu et al. ,Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition.Science381,979-984(2023).DOI:10.1126/science.abq7487
- Pan, L., & Zanolli, C. (2019). Comparative observations on the premolar root and pulp canal configurations of Middle Pleistocene Homo in China.. American journal of physical anthropology, 168 3,637-646https://doi.org/10.1002/ajpa.23777.
- Pan, L., Dumoncel, J., Mazurier, A., & Zanolli, C. (2020). Hominin diversity in East Asia during the Middle Pleistocene: A premolar endostructural perspective.. Journal of human evolution, 148,102888https://doi.org/10.1016/j.jhevol.2020.102888.
- Castro , J. , Martinon‐Torres , M. , Pinillos , M. , Garcia‐Campos , C. , Modesto‐Mata , M. , Martin‐French , L. , & Arsuaga , J. (2019). Metric and morphological comparison between the Arago (France) and Atapuerca-Sima de los Bones (Spain) dental samples, and the origin of Neanderthals. Quaternary Science Reviews. https://doi.org/10.1016/J.QUASCIREV.2018.04.003.
