Early humans were on the brink of extinction, scientists find

Our ancestors’ population fell to only 1280 ‘breeding individuals’ about 930,000 years ago, and remained this low for 117,000 years, research suggests.

Researchers have suggested the population crash 930,000 years ago may have led to the creation of new branches of the human family tree. Picture: Alamy

Our human ancestors almost became extinct about 900,000 years ago, dwindling to a population of less than 1300 adults of reproductive age because of droughts, research has suggested.

Our early ancestors then spent 100,000 years teetering on the brink of extinction, with 98.7 per cent of their population having been wiped out, possibly by catastrophic climatic changes that led to a build-up of ice at the poles and prolonged droughts, a study claims.

Had our ancestors died out, the world of today could have been peopled by Homo erectus and Homo antecessor or even by Neanderthals, experts have said, depending on when the branches of the human family tree diverged. It could even have been entirely free of a human presence, they said.

Genomic analysis of modern humans has allowed scientists to track the genetic diversity, and thus the population size, of our ancestors going back to the early Pleistocene era. They found that it fell to only 1280 “breeding individuals” about 930,000 years ago and remained at this level for 117,000 years.

Including children and older people, this would likely have created a population of a few thousand, according to a study published in the journal Science.

Researchers described the event as a “population bottleneck” that squeezed the entire species down to a very small number.

Scientists from around the world – including the University of Texas, the Shanghai Institute of Nutrition and Health and the University of Florence – took genome sequences from 3154 modern people in 10 African and 40 non-African groups. They analysed the frequency with which certain genetic variations appear in modern humans and used this to analyse the genetic diversity that existed among our human ancestors at key points in the past.

The study notes: “Population size changes that occurred hundreds of thousands of years ago … have left their signatures in the genomic sequences randomly collected from the present-day human population.”

The researchers have suggested the population crash 930,000 years ago may have led to the creation of new branches of the human family tree.

Professor Chris Stringer, an anthropologist at the Natural History Museum, who was not involved in the study, said if the common ancestor of modern humans, Neanderthals and Denisovans, had died out “maybe we would still have descendants of Homo erectus and Homo antecessor [around today]. It could have been a very different planet and a very different story.”

Some evidence suggests the three species had already diverged about a million years ago.

Professor Nick Ashton, of the British Museum’s Institute of Archaeology, who was also not involved with the research, suggested the population crash may have affected the direct ancestors of Homo sapiens in only one part of the world while leaving the ancestors of Neanderthals and Denisovans elsewhere in the world relatively unscathed, suggesting the climatic change “can’t have been a global event”.

He said: “It could have been localised drought in one region, volcanic activity or localised disease.”

Ashton said it raised the thought that “maybe Neanderthals or Denisovans would have survived and we would have a different human species around today or perhaps no humans at all”.

Stringer said performing the same genomic analysis on Neanderthal and Denisovan remains could help to narrow down when our last common ancestor lived by seeing whether their ancestors were also hit by the population slump.

Extinction would have been a real possibility for such a small group, he said. “If they are right, to have that small a number for 100,000 years, they would have been very much at risk of extinction. With that small a population, any major disturbance would really hit them hard.”

The Times