Why Did Our Ancestors Nearly Vanish Around 900,000 Years Ago, With Their Population Dropping to Just ~1,280 Individuals? — Here’s What Scientists Suggest

A new genetic study suggests that the human lineage or our ancestors may have nearly vanished around 900,000 years ago. Scientists found that there were only 1280 individuals who were able to reproduce or contribute to the gene pool of humans from that point on. There may have been other hominins that survived together with them, but these people are the ones who passed on their genes to the next generations.

If these findings turn out to be true or close to what really happened in the past, then our lineage almost faced extinction. They probably needed to survive with such a small population and have been very vulnerable as a species for tens of thousands of years. However, what could have caused this phenomenon, and is a group of around a thousand humans even capable of surviving in their harsh world? Let’s revisit the past and dive deep into these questions.

What May Have Happened — The Drop in Numbers

Genetic data from modern human populations suggests that at one point in time, our lineage almost vanished. It was estimated that this happened around 900,000 years ago and has persisted for hundreds of thousands of years after. The sudden dip in numbers means that something major has happened to the early humans, until their effective population size was only about 1280 individuals.

This does not mean, though, that they are the only humans who have survived. It meant that those 1280 people are the only ones who were able to reproduce and pass on their genes to future generations of humans, including us. These events in history are often called genetic or population bottlenecks.

It is an incredibly dangerous situation that could have easily resulted in the human lineage to just be gone forever. This is because if only few number of individuals survive in the group, referred to as a genetic bottleneck, then it means that the diversity of the gene pool drops. These humans would then be prone to inbreeding, genetic diseases, and be less resilient against pathogens and natural disasters. In other words, they would be heading to the path of extinction.

Read more: Science.org

Why It May Have Happened — Climate, Food & Change

Turns Out, Human Ancestor Almost Went Extinct 900,000 Years Ago

So, if this extinction-level threat was that severe, what type of phenomena could have caused this event? One of the most significant suggestions was climate change. Around 900,000 years ago, Earth was a completely different place than it is now. It is a lot harsher, and the environment was shifting.

There were new types of glacial patterns, causing fluctuating ice ages and droughts. These changes could have negatively impacted the natural habitats of early humans. The areas where they look for food and water could have been depleted. Some regions may have experienced prolonged ice ages, while others could have been exposed to dry climates.

Then these events could have led to an even more dire situation where the early humans may have been fragmented into smaller groups, causing genetic bottlenecks. If so, they would have been more vulnerable to natural disasters like storms or heatwaves. A disease they are not immune to as a population could have also almost wiped them out. So, when the majority of those small groups vanished, only a handful were able to reproduce and pass on their genes.

Another theory could be the speciation of the human species. This phenomenon refers to the process of a new and distinct species forming from the older one. This could have also happened because of the isolation of each group of humans, leading to their genetic pool diverging from the original species. If this is what happened, it could influence the genetic diversity of our lineage.

What the Consequences Could Be — Evolution, Diversity & Survival

So, what are the consequences if the total population of humans were really reduced to a near-extinction level? First, it would have been a lot harder for them to survive new challenges that they could have faced, compared to if their groups were bigger and more diverse.

Their long-term survival would be affected, and some groups may have really suffered local extinctions. This event refers to the specific group of humans living in a particular habitat or migrating together, which was completely wiped out. Either by diseases that they are not well-adapted to, loss of food or water sources, arrival of another human species, or dramatic shifts in climates and temperatures.

Another consequence could be the gap in fossils that scientists have been observing from around this time. If early humans, after the catastrophic events, really were living in small and fragmented groups, then their fossils would have been harder to find, or there would be a scarcity of archaeological sites from this era.

Additionally, this event could have caused or acted as a catalyst for a new species of humans to emerge. One that is very different than that of the older hominins who may have vanished. The genetic bottleneck, over time, may have led to or allowed the formation of human species like Homo heidelbergensis and eventually the modern humans.

Read more: Wikipedia

How Strong Is the Evidence? — Strengths, Doubts & Future

Only 1,000 Humans Survived This Catastrophe

The study has garnered a lot of debate, and further peer reviews would be needed to support the theory and be widely accepted. This is because the fossils and archaeological sites from this period, around 900,000 years ago, are scarce. This fact actually could support the suggestion, as it would mean that early humans may have really faced a genetic bottleneck, and that could explain the gap in fossils.

However, without widespread data and more fossil studies with new supporting DNA and geological evidence, it would remain speculative and theoretical. But it is still amazing that we could find out so much from so few archaeological remains. Whether this event really happened or it is a lot different in reality, one thing is for sure: the human lineage has been able to survive and adapt through all the challenges we have faced so far.

Author's Final Thoughts

The hypothesis that our ancestors may have nearly vanished around 900,000 years ago is both a scary and fascinating idea that reminds us how hard our journey has been before getting to this point. It also served as a lesson that we are not invulnerable to extinction-level threats.

While the evidence is still being reviewed and further studies are needed, this genetic bottleneck theory still helps us understand that human evolution is not a straight and steady path. Instead, it is marked by crisis, hardship, and challenges, but also recoveries, turning points, and the emergence of new species. In other words, our story is a story of survival through it all.

Read next: How Did Homo sapiens’ Mating With Neanderthals, Denisovans, and Other Hominins Over 50,000 Years Ago Alter Human History? — Here’s What Scholars Found

References & Further Reading

Hu, W., et al. (2023). Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition. Science. https://doi.org/10.1126/science.abq7487

Ashton, N. (2023). Did our ancestors nearly die out? Science. https://doi.org/10.1126/science.adj9484

Maslin, M. A., & Brierley, C. M. (2015). The role of orbital forcing in the Early Middle Pleistocene Transition. Quaternary International. https://doi.org/10.1016/j.quaint.2015.01.047

Willeit, M., et al. (2019). Mid-Pleistocene transition in glacial cycles explained by declining CO₂ and regolith removal. Science Advances. https://doi.org/10.1126/sciadv.aav7337

Foerster, V., et al. (2022). Pleistocene climate variability in eastern Africa influenced hominin evolution. Nature Geoscience. https://doi.org/10.1038/s41561-022-01032-y