Humans Almost Went Extinct

Experts recently discovered Humans shrunk down to a mere 1,300 reproducing individuals, before Homo sapiens even evolved

Hiya!

This is a complicated time to be alive. We’re the most advanced and healthiest we’ve ever been, but we're also undergoing unique transitions that challenge us in new ways. Global warming claims millions of lives annually, with the numbers expected to rise yearly. Toss in global pandemics and lower birth rates, and people are understandably concerned about the consequences of a shrinking human population, especially when our entire global economy depends on population increase.

Around 8 billion Humans are alive today, but recent research suggests that about 98.7 percent of the Human population disappeared around 900,000 years ago, leaving less than 1,300 Humans capable of reproducing. Notably, this bottleneck occurred about 500,000 years before our Homo sapien ancestors entered the picture. Meaning that while we dominate the world today, there was a time when we were almost wiped out before we even began.

The Pleistocene Epoch

Okay, so before I get to the study, let’s chat about the time period it relates to. It’s called the Pleistocene Epoch, a cooling period between about 1.9 million and roughly 10,000 years ago.

This epoch is known for its cold climate and for growing massive ice sheets and glaciers, which shaped many of today’s landscapes. There were also severe droughts and, unsurprisingly, widespread food shortages. Fossils discovered during this period show noticeable changes in species in response to a changing planet. Many of the megafauna, such as mastodons, mammoths, and giant sloths, went extinct, while other species on the land and in the water thrived.

Sea levels dropped as the ice sheets and glaciers formed, exposing land once hidden by the water — many of which formed new connections between landmasses once separated. Perhaps the most famous land bridge was the Bering land bridge, connecting today’s Alaska to Russia. For a while, it was thought today’s Central America formed the land bridge between the North and South Americas also occurred during the Pleistocene Epoch, but that’s become debatable.

Anyway, the middle, and especially the late Pleistocene Epoch, is exciting because it’s believed this is when our Homo sapien ancestors began to rise and spread. At the same time, our Neanderthal cousins started to go extinct. The previously described land bridges are thought to have allowed Humans to enter new landscapes, such as the Americas and Australia.

However, there is an unexplained gap in the African/Eurasian Human fossil record from between around 800,000 and 900,000 years ago. But now, a recent study believes we don’t find many Human fossils from that time because Humans underwent a bottleneck that nearly wiped out Homo sapiens’ chance to exist — we didn’t enter the picture until about 300,000 years ago.

The Study

An international team of experts from China, Italy, and the United States published their research in Science, announcing an incredible discovery that could also explain the gap in Eurasian and African fossil records during the Late Pleistocene Epoch.

The researchers studied the genomic data from 3,154 people across 50 populations — 10 African and 40 non-African populations — and compared the emergence of various characteristic genomes within each population.

This allowed the team to trace a person’s various characteristics back to the likeliest population to have produced it. It also allowed them to create a sort of evolutionary timeline of the populations revealed in the samples.

But our genetic data tells us far more than just our likely appearance or family history. It also tells scientists about population fluctuations — even from hundreds of thousands of years ago.

For the study, the team’s leading Chinese geneticists invented the Fast Infinitesimal Time Coalescent process (FitCoal) to trace the various genetic mutations backward in time. Through this method, they could determine population sizes during different evolutionary periods.

Results

When reviewing FitCoal’s results, the team discovered something unexpected. They state:

“Results showed that human ancestors went through a severe population bottleneck with about 1280 breeding individuals between around 930,000 and 813,000 years ago. The bottleneck lasted for about 117,000 years and brought human ancestors close to extinction.”

A population geneticist at the University of Chinese Academy of Sciences in Beijing and the study’s co-author, Haipeng Li, told Nature: “About 98.7 percent of human ancestors were lost.” The team also estimated that this bottleneck could have also lost 65.85 percent of modern genetic diversity. An anthropologist at the Sapienza University of Rome and senior author of the study, Giorgio Manzi, explains in a press release:

“The gap in the African and Eurasian fossil records can be explained by this bottleneck in the Early Stone Age as chronologically, it coincides with this proposed time period of significant loss of fossil evidence.”

Not only does the research help explain the lack of Human fossil evidence from that time, but it also shows that this mysterious Human species survived with these perilously small numbers for over 100,000 years during intense environmental transitions.

When conditions eventually became more hospitable for Human existence — whether because our human predecessor discovered fire or because the climate warmed — this particular species bounced back, allowing future Human lines, like ours, to evolve. The team found that all 10 African populations from the study increased by about 20 times around 813,000 years ago.

But that’s not all.

Not only did this bottleneck threaten our very existence, but the researchers found that it might have contributed to a speciation event — two ancestral chromosomes could have converged to create what’s known as chromosome 2 within modern Humans. If so, the Human species that experienced the bottleneck might have been the last common ancestor shared by Neanderthals, Denisovans, and us, Homo sapiens.

Why?

Once the bottleneck was discovered, the next logical question is, why did it happen? What could have caused the population to plunge to such dwindling numbers?

Unfortunately, genetic data can’t answer such questions — yet — but scientists are well aware of the turbulent climate shifts occurring during that time. As we previously discussed, the Pleistocene epoch was cold, with glaciers, ice sheets, and widespread droughts. So, as of now, climate change is largely believed to have caused such a dramatic decrease in the mysterious Human populations.

Perspective Shift

As concerning and wild as this discovery is, it seems unlikely that the population shrank to such dwindled numbers worldwide. a Paleolithic archaeologist at the British Museum, Nick Ashton, who wasn’t involved with the study, points out that other archaeological sites in Eurasia and Africa date to the supposed bottleneck timeframe, suggesting the bottleneck occurred in certain areas, such as within Africa, rather than worldwide.

Considering you and I are two of around 8 billion humans on this planet, the sample size of 3,100-ish people is pretty small. It would be interesting to replicate the study using a much larger data set. Regardless, the results are fascinating to consider. If the bottleneck did result in a lineage split, one of which created us, then the discovery is even more unique. I mean, what are the odds of capturing our speciation event?

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Photo by Keith Hardy on Unsplash