***Science Today*** Unlocking the Enigma of Human Survival: The Mystery of the 100,000-Year Transition

Unlocking the Enigma of Human Survival: The Mystery of the 100,000-Year Transition

Revealing the Near-Extinction Event and Evolutionary Breakthroughs of Our Ancestors

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Introduction

The Quaternary Period, a geological epoch that spans from approximately 2.6 million years ago to the present day and is synonymous with the Ice Age, has captivated scientists for its cyclic climate shifts and the ebb and flow of ice caps. Yet, concealed within this grand narrative, a profound mystery has persisted for over a million years – the transition from shorter, milder Ice Age cycles to prolonged, severe ones. Genetic analysis now suggests that our early hominid ancestors faced a near-extinction event during this period, raising questions about their resilience and adaptation.

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The Mysterious Transition

Around 1.1 million years ago, a remarkable shift occurred in the glacial cycles of the Ice Age. Initially, they followed a 41,000-year periodicity, resulting in relatively thin ice sheets and mild effects on the planet. However, suddenly, these cycles lengthened to about 100,000 years and intensified both in amplitude and cooling. This unexpected alteration in climate patterns, the "hundred-thousand-year problem," has confounded scientists due to its abruptness and unknown causes.

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Discovering the Near-Extinction Event

Recent genetic studies have unveiled crucial evidence shedding light on this enigmatic period. Researchers analysed the DNA of over 3,000 individuals worldwide, including 10 African and 40 non-African populations. Employing a novel method called "fit coal fast infinitesimal time coalescent process," they traced changes in DNA over time. The results unveiled a stark population bottleneck around 930,000 years ago, lasting for a staggering 117,000 years. Genetic diversity plummeted by approximately 66%, an indication of a population under duress.

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Population Bottlenecks in History

While the concept of population bottlenecks is not new in genetic research, the extent and impact of the bottleneck during this period are unprecedented. Earlier studies identified a bottleneck about 7,000 years ago, impacting regions across Africa, Europe, and Asia. This bottleneck was attributed to the collapse of the Y chromosome, leading to a significant gender imbalance with one man for every 17 women. However, it was primarily attributed to cultural shifts rather than environmental factors.

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The Astonishing Genetic Contraction

In contrast, the genetic analysis of the period around 1.1 million years ago suggests a far more severe scenario. The total population of hominids on Earth dwindled from roughly 100,000 to a mere 1,200 individuals. This marked a staggering 99% drop in genetic diversity and persisted for over a hundred millennia. The near-extinction event suggests that the early human ancestors struggled for survival during this extraordinary climatic shift, likely due to unpreparedness and resource depletion.

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Evolution Amidst Crisis

While the bottleneck represents a dire episode in our history, it also coincides with significant evolutionary developments. Notably, human chromosomes merged during this period, resulting in the formation of a substantial chromosome 2 – the second-largest chromosome in the human body. This genetic event is believed to have distinguished humans from other great apes. Additionally, the complexity of the human brain expanded, potentially enabling our ancestors to devise innovative solutions despite dwindling numbers.

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Unravelling the Climate Connection

Although the genetic evidence hints at a close relationship between the near-extinction event and climatic changes, causation remains elusive. Evidence of extreme cold in regions like Portugal, where fossils suggest ocean temperatures of at least minus 6 degrees Celsius, raises questions about the hostile Mediterranean climate around 1 million years ago. However, a direct link between climate and the population bottleneck is yet to be established.

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Conclusion

In the annals of our ancient history, the narrative of near extinction stands as a powerful testament to the resilience and adaptability of our early hominid forebears. This chapter illuminates the intricate interplay of climate, genetics, and evolution that has shaped the course of our species over vast stretches of time. As we venture deeper into Earth's past, we unravel the mysteries that have indelibly marked our lineage and provoke contemplation of our future as the reigning species on this planet.

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Question for Reflection:

Considering past extinctions, what species, if any, do you think could potentially become the next dominant species after humans? Please leave your answers in the comments below.

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