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Human history is packed with miraculous tales of survival, but none, perhaps, surpass the one which occurred approximately 800,000 years ago. A seminal report in Science informs us that early humans saw the global population decrease dramatically to an all-time low of only 1,280 breeding adults. This near wipeout event, an “ancestral bottleneck,” continued for fully 117,000 years and came very close to eliminating our species.
What Was the Ancestral Bottleneck?
The ancestral bottleneck refers to a period when the early human population drastically declined to a dangerously low level. Researchers estimate that nearly 98.7% of the population vanished, leaving only about 1,280 breeding individuals on Earth.
This event is believed to have taken place between 800,000 and 900,000 years ago and lasted for an astonishing 117,000 years. During this time, early humans were on the verge of extinction, struggling to survive in harsh environments.
Scientists believe that this event played a significant role in shaping the evolution of modern humans, possibly leading to key genetic changes that set Homo sapiens apart from other hominin species like Neanderthals and Denisovans.
How Do Scientists Know This Happened?
Understanding an event that took place nearly a million years ago is no easy task. So how did scientists uncover this near-extinction?
1. The FitCoal Method
Researchers used a groundbreaking genetic analysis method called FitCoal (fast infinitesimal time coalescent process). This tool analyzes genetic data from modern human populations to trace back ancient demographic changes.
By studying the DNA of 3,154 people from 10 African and 40 non-African populations, scientists were able to detect the massive drop in population that happened 800,000 years ago.
2. The Missing Fossil Record
Another clue comes from the lack of fossils from this period. There is a significant gap in the fossil record from Africa and Eurasia, which has puzzled scientists for years. The new study suggests that this gap might be explained by the drastic reduction in human numbers during the bottleneck.
3. Loss of Genetic Diversity
According to the study, nearly 65.85% of genetic diversity was lost due to this population decline. A loss of genetic diversity means that fewer genetic traits are passed on, which could have made survival even more challenging for our ancestors.
What Caused the Population Crash?
While scientists cannot pinpoint a single cause, the most likely reasons for this drastic population drop include:
1. Extreme Climate Changes
During this period, the Earth’s climate underwent massive fluctuations. These changes included:
- Severe droughts that dried up water sources
- Colder temperatures that made survival more difficult
- Changing ecosystems that disrupted food availability
These harsh conditions could have led to food shortages and increased competition for resources, pushing early humans to the brink of extinction.
2. Food Scarcity and Extinction of Large Animals
Early humans relied on hunting large animals like mammoths, mastodons, and giant sloths. However, during this period, many of these species went extinct or became harder to find. This lack of food likely contributed to the decline in human populations.
3. Natural Disasters
Catastrophic events such as volcanic eruptions, earthquakes, or massive wildfires could have further worsened the situation. These disasters might have wiped out key habitats, making survival even harder.
How Did Humans Endure?
Despite facing extreme conditions, some small groups of humans managed to survive. But how did they survive?
1. The Mastery of Fire
One theory suggests that early humans learned to control fire during this period. Fire would have been essential for:
- Cooking food, making it easier to digest
- Keeping warm in cold environments
- Scaring away predators and providing safety at night
Fire may have been a crucial survival tool that helped small groups endure the harsh climate.
2. Migration and Adaptation
Some early humans may have migrated to areas with better food and water sources. By adapting to new environments, these small groups could have found ways to survive despite the challenges.
3. Cooperation and Social Structures
Survival in harsh conditions likely strengthened social bonds among early humans. By working together in small groups, they could have:
- Shared food and resources
- Protected each other from predators
- Passed down knowledge about survival strategies
This social cooperation may have laid the foundation for the advanced societies we see today.
How Did This Event Influence Human Evolution?
Interestingly, this event of near-extinction could have been instrumental in the development of modern humans. Scientists believe it led to two major evolutionary changes:
1. Chromosome Fusion and the Origin of Homo Sapiens
One of the most interesting discoveries of this research is that this bottleneck could have resulted in a genetic innovation—the merging of two ancestral chromosomes into chromosome 2 in contemporary humans. Chromosome 2 is a large human chromosome with 243 million base pairs. This genetic change might have:
- Helped differentiate Homo sapiens from Neanderthals and Denisovans
- Played a role in brain development and intelligence
- Contributed to the eventual success of modern humans
2. Natural Selection and Brain Evolution
Surviving such extreme conditions would have required problem-solving skills, adaptability, and innovation. This may have led to:
- Increased intelligence in early humans
- The development of early tools and technology
- Better survival instincts
These evolutionary changes may have helped our ancestors thrive once the climate improved and contributed to the rapid expansion of Homo sapiens.
The Recovery: How Humans Bounced Back
Around 813,000 years ago, human populations began to recover. This was likely due to:
- A more stable climate
- The spread of new survival strategies
- The gradual increase in genetic diversity
This recovery marked the beginning of a new chapter in human evolution, eventually leading to the global spread of modern humans.
