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Tracing humanity’s survival -

Research by molecular biologists at Oxford suggests that humanity once dwindled to around a thousand reproductive adults, while author Sam Kean posits that the number may have been as low as forty. The implications of this are astounding: how could such a small group grow into the 7.8 billion people alive today?

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A case of modern genetic bottleneck -

Northern elephant seals provide a modern example of a severe population bottleneck. By the 1890s, relentless human poaching had reduced their numbers to as few as 20 individuals. This drastic decline significantly diminished the genetic diversity within the species, a legacy still evident in today’s populations.

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A case of modern genetic bottleneck -

Despite coming back from the brink of extinction with a current population exceeding 30,000, northern elephant seals still bear the genetic scars of their near-demise. In contrast, southern elephant seals, which were not subjected to the same level of hunting, exhibit far greater genetic diversity.

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The risks of bottlenecks -

Small populations face heightened vulnerability to diseases and environmental catastrophes, while unfavorable genetic traits can accumulate more rapidly. Genetic bottlenecks also hinder evolutionary progress, as fewer individuals limit the chance for beneficial mutations to emerge and spread within the species.

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How bottlenecks shaped human diversity -

Genetic bottlenecks often lead to the founder effect, where small, isolated populations diverge significantly from their original gene pool. As humans dispersed across the globe, our species experienced several bottlenecks, which triggered a serial-founder effect, contributing to the remarkable genetic diversity observed in the human race today.

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Migration and genetic diversity -

Scientists have identified key geographic choke points where genetic diversity decreased as humans migrated across the planet. One significant bottleneck occurred when a small group of humans left Africa, marking a pivotal moment in the spread of our species and shaping the genetic makeup of populations around the world.

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Migration and genetic diversity -

African populations exhibit significantly greater genetic diversity compared to populations native to the Americas, which can be attributed to the bottlenecks and migrations that occurred as humans dispersed from Africa. When compared to other species, human DNA shows relatively low diversity considering our global distribution and vast range.

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A world of humans -

Until approximately 30,000 years ago, the planet was home to at least five human species. Homo sapiens, our ancestors, primarily inhabited East Africa. Meanwhile, Neanderthals resided in Europe, and Homo erectus occupied regions of Asia, among others.

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Neanderthal legacy -

The mapping of the Neanderthal genome led to a remarkable discovery: individuals of European descent today carry up to 4% of their genetic material from Neanderthal ancestors. This evidence of interbreeding between Homo sapiens and Neanderthals offers a fascinating glimpse into our shared evolutionary history.

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The volcanic eruption that shaped humanity -

The cause of humanity's bottleneck around 70,000 BCE can be traced to the eruption of the Toba volcano in Indonesia. This was no ordinary event, as approximately 650 cubic miles (2,709 cubic kilometers) of rock were vaporized and ejected into the atmosphere. 

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The volcanic eruption that shaped humanity -

The Toba eruption, also referred to as the Toba supereruption or the Youngest Toba eruption, was a supervolcanic event that took place at the location of present-day Lake Toba in Sumatra. It stands as one of the most significant volcanic events in Earth's history.

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The scale of supervolcanic power -

To grasp the magnitude of Toba's eruption, consider these comparisons: Mount St. Helens erupted in 1980, releasing approximately 0.62 cubic miles (1 cubic kilometer) of rock; Vesuvius, in 79 CE, ejected approximately 1.86 cubic miles (3 cubic kilometers); and Tambora's 1815 eruption unleashed an extraordinary 40 cubic miles (80 cubic kilometers). 

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The scale of supervolcanic power -

The Toba eruption unleashed an astonishing 1,739 cubic miles (2,800 cubic kilometers) of material, dwarfing all other recorded volcanic events. Its impact was so immense that layers of ash from the eruption remain visible across vast regions of South Asia and the Indian Ocean, serving as a stark reminder of its unprecedented scale.

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A dimmed sun -

The Toba eruption released immense amounts of material into the atmosphere, with dust and ash lingering in the upper sky and likely dimming sunlight for up to six years. For early humans, this created dire conditions that were nearly fatal. 

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Toba’s aftermath -

The diminished sunlight and eruption fallout disrupted seasonal rains, dried up streams, and caused a scarcity of vital resources such as berries, fruits, and trees, making survival incredibly challenging.

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Toba’s aftermath -

The event also triggered a harsh volcanic winter, which led to a cooling period on Earth that lasted approximately 1,000 years.

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Climate models and regional effects -

Lead author Benjamin Black from Rutgers University highlights findings from extensive climate model simulations that address an apparent paradox. The results suggest that previous assumptions about the Toba eruption's global cooling effects may have overlooked regional variations.

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Surviving Toba -

For example, archaeological evidence indicates that human hunter-gatherer settlements in India were not severely impacted by the Toba eruption and recovered relatively quickly.

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Surviving Toba -

Similarly, temperature data preserved in the geology of Lake Malawi, East Africa, suggests that the region experienced less dramatic cooling than previously assumed, demonstrating the varying regional effects of the volcanic event.

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Probing climate disruptions -

Researches developed a probabilistic assessment of the eruption's climatic impact using 42 global climate model simulations to examine the potential climate disruptions caused by the Toba eruption, by varying factors such as the magnitude of volcanic emissions, eruption timing, background climate conditions, and eruption column height.

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Toba’s cooling effects -

The findings indicate substantial regional differences in the climate impacts of the Toba eruption. According to the simulations, the Northern Hemisphere experienced cooling of at least 39°F (4°C), with some regions facing temperature drops as extreme as 50°F (10°C), depending on the model parameters.

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Rethinking Toba -

The findings align with archaeological evidence indicating that the Toba eruption had relatively modest impacts on the development of hominid species in Africa. 

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The Southern Hemisphere -

In the Southern Hemisphere, where early human populations were present, even the most extreme eruption scenarios suggest cooling was unlikely to exceed 39°F (4°C). 

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The Southern Hemisphere -

However, regions such as southern Africa and India may have experienced reduced precipitation and even severe drought, particularly under the highest volcanic emission levels.

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Preparing for future volcanic risks -

According to co-author Dr. Anja Schmidt from the University of Cambridge, research not only serves as a forensic investigation into the Toba eruption’s aftermath, but also provides insights into the uneven effects that large-scale volcanic eruptions may have on modern societies. 

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Rethinking Toba -

The findings align with archaeological evidence indicating that the Toba eruption had relatively modest impacts on the development of hominid species in Africa. 

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From near extinction to resilience -

Humanity’s story mirrors a great triumph after despair. Nearly wiped out, humans bounced back, but growth was slow. It took over 200,000 years for the population to reach 1 billion by 1804—a testament to our resilience and gradual expansion.

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The population boom -

The first billion took millennia, but humanity has since seen exponential growth. By 1960, the population hit 3 billion, and nearly a billion more people have been added approximately every 13 years since, which is a rapid expansion that shapes the modern world.

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Humanity at a crossroads -

Some scientists predict that humanity will eventually face extinction and even suggest potential timelines. The Bulletin of Atomic Scientists recently warned that the risk of global catastrophe is "very high," citing nuclear weapons and climate change as the most urgent existential threats to our survival.

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A future in question -

With world leaders acting irrationally and struggling to address humanity’s most pressing issues, it’s natural to question the sustainability of our current path. From escalating climate crises to global security threats, the clock is ticking, and decisive action is more urgent than ever.

Sources: (The Bulletin of Atomic Scientists) (University of Cambridge) (Rutgers University) (Forbes) (NPR)

See also: Historical mysteries solved by science in 2024

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