Scientists unearthed a major population bottleneck between 930,000 and 813,000 years ago, resulting in a 65.85% loss in genetic diversity.
Delving into humanity’s ancient past can often read like a gripping suspense novel. Recent studies suggest that almost a million years ago, an unfathomable event brought our forebearers to the brink of extinction.
Modern human genomic studies paint a stark picture: From a thriving community of about 100,000, a staggering event dwindled the population down to a mere 1,280 fertile individuals. This staggering 98.7% reduction, spanning 117,000 years, threatened to erase the very essence of humanity.
Bridging Gaps in Our Past
Yet, our vast numbers today stand as a testament to survival. Geneticists Haipeng Li of the Chinese Academy of Sciences and Yi-Hsuan Pan from East China Normal University point to this event as an answer to a long-standing enigma: the curious void in the Pleistocene human fossil records. Anthropologist Giorgio Manzi from Sapienza University in Rome asserts this bottleneck in the Early Stone Age aligns perfectly with the missing fossil evidence, filling a vital historical gap.
Population bottlenecks, substantial reductions in species numbers due to events like famines, wars, or climatic changes, aren’t rare. Such drops in genetic diversity manifest in the descendants, evidenced by a Northern Hemisphere human bottleneck just 7,000 years ago. But as researchers journey further back in time, extracting clear data becomes increasingly intricate.
To address this, the researchers pioneered a new technique named the fast infinitesimal time coalescent process (FitCoal). By leveraging FitCoal on the genetic data of over 3,000 individuals globally, the team unearthed a major population bottleneck between 930,000 and 813,000 years ago, resulting in a 65.85% loss in genetic diversity.
Zeroing In on Potential Causes
While pinpointing an exact cause remains elusive, the dramatic Mid-Pleistocene Transition, marked by severe glaciation cycle shifts, stands as a probable catalyst. This climate upheaval may have triggered harsh conditions, ushering in famine and conflict, further slashing population numbers.
Pan states, “This revelation opens up a new dimension in our understanding of human evolution.” Questions abound, ranging from the habitats of these early humans, their coping mechanisms during these climatic adversities, and whether this bottleneck expedited human brain evolution.
A Genetic Twist: The Chromosome 2 Formation
Interestingly, this bottleneck might have spurred a unique feature in the human genome: the merger of two chromosomes resulting in chromosome 2. While we possess 23 chromosome pairs, our closest kin – the great apes – have 24. This chromosome formation potentially set humans on a distinct evolutionary trajectory.
“Such discoveries only scratch the surface,” comments Li, emphasizing the continuous journey to fully grasp human evolution during this tumultuous period, ultimately unlocking the enigma of our early ancestry.
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