Humans may have come close to
extinction about 70,000 years ago, according to the latest genetic
By Dr David Whitehouse
BBC News Online science editor
suggests that at one point there may have been only 2,000 individuals
alive as our species teetered on the brink.
From just a few, six billion
This means that, for a while, humanity was in a perilous state,
vulnerable to disease, environmental disasters and conflict. If any of
these factors had turned against us, we would not be here.
The research also suggests that humans (Homo sapiens sapiens)
made their first journey out of Africa as recently as 70,000 years ago.
Unlike our close genetic relatives - chimps - all humans have virtually
identical DNA. In fact, one group of chimps can have more genetic
diversity than all of the six billion humans alive today.
It is thought we spilt from a common ancestor with chimps 5-6 million
years ago, more than enough time for substantial genetic differences to
The absence of those differences suggests to some researchers that the
human gene pool was reduced to a small size in the recent past, thereby
wiping out genetic variation between current populations.
Evidence for that view is published in the American Journal of Human
Because all humans have virtually identical DNA, geneticists look for
subtle differences between populations.
One method involves looking at so-called microsatellites - short,
repetitive segments of DNA that differ between populations.
These microsatellites have a high mutation, or error, rate as they are
passed from generation to generation, making them a useful tool to study
when two populations diverged.
Researchers from Stanford University, US, and the Russian Academy of
Sciences compared 377 microsatellite markers in DNA collected from 52
regions around the world.
Analysis revealed a close genetic kinship between two hunter-gatherer
populations in sub-Saharan Africa - the Mbuti pygmies of the Congo Basin
and the Khosian bushmen of Botswana.
The researchers believe that they are "the oldest branch of modern
humans studied here".
The data also reveals that the separation between the hunter-gatherer
populations and farmers in Africa occurred between 70,000 and 140,000
years ago. Modern man's migration out of Africa would have occurred after
An earlier genetic study - involving the Y chromosomes of more than
1,000 men from 21 populations - concluded that the first human migration
from Africa may have occurred about 66,000 years ago.
The small genetic diversity of modern humans indicates that at some
stage during the last 100,000 years, the human population dwindled to a
very low level.
It was out of this small population, with its consequent limited
genetic diversity, that today's humans descended.
Estimates of how small the human population became vary but 2,000 is
the figure suggested in the latest research.
"This estimate does not preclude the presence of other populations of
Homo sapiens sapiens (modern man) in Africa, although it suggests
that they were probably isolated from each other genetically," they say.
The authors of the study believe that contemporary worldwide
populations descended from one or very few of these populations.
If this is the case, humanity came very close to extinction.