It was a very close call.
If a devastating drought that gripped Africa had lasted just a little longer, or been a little worse, we would not be here today.
There would be no humans, no cities, no art and no science. There would be no wars and no human-induced climate change. The world would belong to the animals.
An international genetics project has found that modern humans almost became extinct 70,000 years ago.
The Genographic Project, led by American and Israeli researchers, made the discovery after undertaking the most extensive mitochondrial DNA survey ever undertaken in Africa.In 1987 a study of mitochondrial DNA, passed down the generations via the maternal line, revealed that every person alive today is descended from one woman who lived in Africa 200,000 years ago.
The latest study shows that after the birth of humanity in eastern Africa, people quickly split into separate communities.
About 150,000 years ago humans, possibly pursuing animal herds, moved to settle throughout Africa. The number of people soared, peaking somewhere between 10,000 and 100,000.
But before the first person could venture out of Africa, the population suddenly crashed to just 2000.
"It could have been even fewer," said Spencer Wells, the Genographic Project director. "We were, in effect, hanging on by our fingertips."That's fewer people than there are Sumatra orang-utans today, and they are classified as extremely endangered and will probably go extinct in 20 years."
The crisis was probably caused by climate change. About 130,000 years ago the world started cooling and drying as it neared another ice age."There were massive droughts in Africa ... mega-droughts," Dr Wells said. With much of the continent barren and hostile, the tiny human settlements became isolated from each other.
As humanity hovered on the edge of extinction "a shift in culture began. People began making the better hunting tools they needed to survive the drought. Art makes its appearance. There is abstract thought," he said.
Then the drought broke. Isolated communities migrated and merged. With better skills and a friendlier climate, the population boomed again and people finally left Africa, spreading along the Asian coast, towards Australia.
Backed by National Geographic and IBM, the researchers, who have published their findings in The American Journal Of Human Genetics, identified humans' near demise after studying DNA mutation rates.
"By sampling people alive today, estimating how much genetic variation they have ... and knowing the rate at which variation accumulates we can say how long it took to accumulate the observed level of variation, and the size of the starting population," Dr Wells said.
The project aimed to discover what humans were doing before leaving Africa.
"Three quarters of our history is virtually unknown," Dr Wells said. The research showed "there was lots going on".
He believes humanity's close shave should send a message to the 6.6 billion people alive today. "We should start to see ourselves as the lucky survivors."