How Our Human Ancestors Survived a Near-Extinction Event 900,000 Years Ago

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6 Sept 2023

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Imagine a world where only a few thousand people are alive, struggling to survive in harsh conditions. This is not a dystopian scenario, but a reality that our human ancestors faced 900,000 years ago, according to a new study published in the journal Science.

The study suggests that the population of early humans that gave rise to modern humans, Neanderthals, and Denisovans was reduced to around 1,280 individuals during a time of dramatic climate change.

How did they manage to survive and thrive after such a near-extinction event? What impact did it have on their evolution and diversity? These are some of the questions that the researchers tried to answer using a novel technique that analyzes modern genetic data.

The Population Bottleneck

The researchers, led by Wangjie Hu from the Chinese Academy of Sciences, developed a statistical method that uses genetic information from 3,154 present-day human genomes to infer the size of populations at specific points in the past.

They found that between 813,000 and 930,000 years ago, the population of our ancestral lineage experienced a severe bottleneck, meaning that their numbers plunged dramatically to a point where they were within a whisper of extinction. Based on their estimates, some 98.7 percent of our human ancestors were wiped out.

What caused this population crash? The researchers suggest that it coincided with dramatic changes in climate during what’s known as the mid-Pleistocene transition, when glacial periods became longer and more intense, leading to a drop in temperature and very dry climatic conditions. These environmental challenges may have reduced the availability of food and water, increased the risk of disease and predation, and disrupted the social and cultural networks of early humans.

The Survival Strategies

How did our human ancestors cope with such a dire situation? The researchers propose that they may have adopted some survival strategies that helped them overcome the bottleneck and eventually increase their population size around 813,000 years ago. Some of these strategies are:

Fire control: The ability to use fire for cooking, warmth, protection, and communication may have been crucial for early humans to adapt to the cold and dry climate. The earliest evidence of fire use for cooking dates from 780,000 years ago in what is now modern-day Israel.
Migration: Early humans may have moved to regions with more favorable conditions or resources, such as Africa or Asia. This may have also facilitated gene flow and hybridization with other hominin species, such as Neanderthals and Denisovans.
Innovation: Early humans may have developed new tools, behaviors, or cognitive abilities that enhanced their survival and reproduction. For example, they may have improved their hunting skills, social organization, or language.

The Evolutionary Consequences

The population bottleneck may have also had some evolutionary consequences for our human ancestors. The researchers speculate that it may have led to:

Loss of diversity: The bottleneck may have reduced the genetic diversity of early humans by increasing inbreeding and genetic drift. This may have made them more vulnerable to diseases or environmental changes.
Speciation: The bottleneck may have triggered the emergence of a new hominin species that was a common ancestor of modern humans, Neanderthals, and Denisovans. The timeline of the bottleneck matches some existing genetic estimates that suggest that this species diverged from other hominins around 900,000 years ago.
Selection: The bottleneck may have increased the intensity of natural selection on early humans by exposing them to new challenges and opportunities. This may have accelerated the evolution of their brain size, morphology, or behavior.

Conclusion

The study by Hu and colleagues reveals how our human ancestors survived a near-extinction event 900,000 years ago using modern genetic data. It also raises many questions about the places where these individuals lived, how they interacted with other hominins, and what traits they passed on to their descendants. The study is a remarkable example of how science can uncover the secrets of our past and help us understand our present and future.

References

Human ancestors nearly went extinct 900,000 years ago | Nature
Scientists say they have pinpointed the moment humanity almost went extinct | MSN
Our Human Ancestors Very Nearly Went Extinct 900,000 Years Ago | Smithsonian Magazine
Early humans nearly went EXTINCT 900,000 years ago when the population of our ancestors dropped to just 1,280 individuals, study claims | MSN
Human ancestors nearly died out 900,000 years ago, study suggests | CNN
Our Human Ancestors Almost Went Extinct Around 900,000 Years Ago: Study | Business Insider

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