The Extinction Event That Once Reduced Humanity To 1,300 People

The next time you walk down a packed city street, stroll around a mall, or wade through a concert crowd take a look around and ask yourself, "What if these people were the only people alive?" As in: take that group of people and disperse it across the entire globe, and that's the entirety of Earth's human population across every settlement, tribe, industry, profession, and more. We'll put it this way: You'd better hope there's at least one medical doctor in there, or one person who knows how to grow crops, or one person with mechanical know-how. And if some great disaster happens at that point? Well, this whole human consciousness and civilization experiment might just be gone for good.

In fact, this exact scenario already happened. Granted, back then civilization was still at the hunter-forager phase, so there was arguably much less to lose, but in today's crowded world it's hard to fathom what it would be like to live on a planet where the total population of our human ancestors was about the same as that of a large high school. 

This at-risk phase didn't last for 20 years or even 200, though. As a recent article from the journal Science says, it lasted for about 117,000 years. From 930,000 to 813,000 years ago environmental conditions on Earth funneled our human ancestors into a protracted "population bottleneck." The entirety of the human population, all on the African continent, got culled from an already mere 100,000 to about 1,280 "breeding individuals," i.e., members of the species capable of producing offspring. But, these hardy folks survived, and if something similar happens to us, so should we.

To be clear, when we talk about "humans" almost going extinct 900,000 to 800,000 years ago, we're not talking about anatomically modern Homo sapiens. As Smithsonian Magazine outlines, we've tallied 22 different human species going all the way back to 7 million years ago and Sahelanthropus tchadensis, the first human in west central Africa to show signs of upright posture and smaller canine teeth. By the time the population bottleneck happened the key human species on the scene was Homo erectus, the most successful and long-surviving human species that existed all the way from 1.89 million to 110,000 years ago. 

It's Homo erectus who bore the brunt of the population bottleneck. The Guardian speculates that the extreme pressure to survive and the environmental conditions of the time might have directly contributed to speciation — the branch-like divergence of different species — and the rise of subsequent human species: Homo heidelbergensis (the first humans to control fire), Homo neanderthalensis (our closest human cousins), and us, Homo sapiens. A handy species family tree at Smithsonian Magazine outlines the speciation of humanity through time, including during the recently discovered population bottleneck.

Professor Chris Stringer at the Natural Museum of London told The Guardian of the 117,000-year-long bottleneck and its 1280-human population, "It's an extraordinary length of time. It's remarkable that we did get through at all. For a population of that size, you just need one bad climate event, an epidemic, a volcanic eruption and you're gone."

Popular Science has a fairly detailed diagram showing humanity's population numbers going back about 1 million years, which overlaps with Earth's Pleistocene Era, a span of time stretching all the way from about 2.5 million years ago to a scant 11,700 years ago. This was an era when the polar ice sheets stretched all the way down to southern Italy at 37 degrees north and receded very, very slowly. The end of the Pleistocene Era, which marked the beginning of the modern Holocene era, very non-coincidentally coincided with the first marks of human agriculture and advanced civilization in the Middle East, as the journal PNAS on the National Library of Medicine outlines. 

As the Popular Science diagram shows, there were about 98,130 humans alive prior to about 930,000 years ago, which shrunk to 1,280 people for 117,000 years. After this the population stayed at a stable, but still meager, 21,160 all the way to Homo sapiens' mass exodus from the African continent about 100,000 years ago.

These kinds of finds only became recently possible thanks to a genetic sequencing method that researchers dubbed "FitCoal:" fast infinitesimal time coalescent process, per Popular Science. Researchers only needed genetic samples from 3,154 current people to trace genetic markers all the way back to the bottleneck period. Previously, archaeologists had discovered a severe lack of fossils from the time period in question, which thanks to the work of the current study now makes a lot more sense.