Humans Almost Went Extinct 900,000 Years Ago, With Only About 1,280 Breeding Individuals Alive

Scientists say the human population crashed between 800,000 and 900,000 years ago. What could have happened?

According to a new study published in Science, a genomic analysis of more than 3,000 living people suggested that our ancestors’ total population plummeted to about 1,280 breeding individuals for about 117,000 years. This is an extremely low number for a species to survive and reproduce.

The researchers behind the study used a new statistical method to estimate the timing and sizes of ancient breeding populations using patterns of shared gene variants in human populations today. They compared the genetic diversity of modern Africans, Europeans and Asians with different hypothetical scenarios of ancient population histories. They found that the best scenario that matched the data was one that involved a severe population crash between 800,000 and 900,000 years ago.

What could have caused this evolutionary bottleneck? The scientists believe that an extreme climate event could have led to the near-extinction of our ancestral line. Previous geologic evidence indicates that this period coincided with significant changes in global climate that turned glaciations into long-term events, a decrease in sea surface temperatures, and a possible long period of drought in Africa and Eurasia.

The decline also appears to coincide with a relatively empty period on the fossil record of early humans. “We know that between about 900,000 and 600,000 years ago, the fossil record in Africa is very scarce, if not almost absent, while both before and after we have a greater number of fossil evidence,” said Prof Giorgio Manzi, an anthropologist at Sapienza University of Rome and a senior author of the research. “The same can be said for Eurasia: for example, in Europe we have a species known as Homo antecessor around 800,000 years ago and then nothing for about 200,000 years.”

However, the researchers also speculate that the population bottleneck could have triggered the emergence of a new species, Homo heidelbergensis, which some believe is the shared ancestor of modern humans and our cousins, the Neanderthals and Denisovans. Homo sapiens are thought to have emerged about 300,000 years ago.

“It was lucky [that we survived], but … we know from evolutionary biology that the emergence of a new species can happen in small, isolated populations,” said Manzi.

This study sheds new light on the evolutionary history of our species and reveals how close we came to being wiped out by environmental factors. It also raises questions about how our ancestors adapted to such harsh conditions and what genetic changes occurred during this critical period.

Sources: 1, 2, 3