The descendants of the first humans to leave Africa thousands of years ago shrank to little more than 1,000 before expanding rapidly, a new study has revealed.
Scientists discovered the population of the ancestors of modern Asian and European people dwindled to just 1,200 who were 'actively reproducing'.
They also found that African populations crashed to around 5,700 people.
And contrary to popular opinion, the study revealed that these early humans continued to breed with sub-Saharan Africans until as recently as 20,000 years ago.
The findings were made by genome scientist Richard Durbin and his then research assistant Heng Li at the Wellcome Trust Sanger Institute near Cambridge.
They mined the publicly available DNA sequence of American biologist Craig Venter - who was one of the first to sequence the human genome- as well as the sequences from six other people.
By taking just a single person's genome, the pair were able to learn an entire population's history from it.
Traditionally geneticists eager to look back at human history have compared DNA sequences from numerous people around the world to determine how different populations relate to one another and when they might have gone their separate ways.
But they have now found that part of a person's genome - which stores hereditary information - can also be followed back in time to when just one version - a common ancestor- existed.
John Novembre, a population geneticist at the University of California, Los Angeles, explained the theory to Nature.com.
'Each little piece of the genome has its own unique bit of history and goes to a unique ancestor as you go further and further back.
'As you look at different parts of the genome, you get access to different parts of history.'
Using this theory Mr Durbin and Mr Li were able to determine a way to calculate - from the ages of different segments of a single person's genome - changes in the population size of our ancestors.
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