Early ancestors came close to extinction
DNA analyses of modern populations show that our common ancestor was close to extinction almost a million years ago. Sudden climate change is believed to have caused the population to drop by almost 99%. definite contact between branches – i.e. an exchange of genes, though without the groups merging completely.
The results suggest that our species evolved via complex interaction between different groups that were scattered across the African continent. These groups were isolated from each other for periods of time, but not for long enough to evolve in completely different directions. They must have met periodically, exchanged genes, then separated again.
The main reason for this dynamic is probably climate change. During dry periods, our ancestors may have migrated to the north, east and south coasts, where they were cut off from each other. But in wetter periods, when the Sahara was green and lush, they migrated towards the centre of the continent, where they could meet and exchange genes.
In other words, our species was not conceived in one place in a linear fashion. It is the fruit of a long series of encounters between adventurous and amorous precursors of Homo sapiens all over Africa.
However, if we follow the new family tree much further back in time – to around 700,000 years before our species came into existence – all the branches do meet in one point: so this is a root of the family tree, humankind’s common starting point. And another new study sheds light on where this root is located.
Researchers find the root
In another comprehensive analysis, a group of US, UK and Austrian researchers led by the UK’s University of Oxford used DNA sequencing of 3609 genomes from 215 population groups around the world. The researchers travelled back in time generation after generation, determining when the groups split – and where it likely happened, by assuming that separations occurred geographically midway between the location of the two new generations. The researchers put all the data into a computer animation (use this QR code to see it) which shows our distribution
shrinking as we go back in time, returning to the origin point where it converges, two million years ago – in Sudan.
Sudan has not been considered a vital location in our species’ early history. So controversial are changes to the human narrative that the researchers emphasised the possible weakness of their ‘picking a midpoint’ geography. Still, the method provides a rough and probably best yet estimate of humankind’s common point of origin. From this origin, our ancestors spread across Africa and gradually developed the traits we recognise in ourselves. The different groups mixed and matched their genes, and from this tangled family tree, our Homo sapiens species eventually emerged. However, as revealed in our News section last issue, our ancestors had come dangerously close to extinction.
We are lucky to be here
A large DNA project by Chinese, Italian and US researchers in 2023 revealed that a key early ancestor in our evolutionary lineage came very close to disappearing around 900,000 years ago. The researchers arrived at the result by analysing DNA sequences from a total of 3154 people from 10 African population groups and 40 groups from outside Africa. Based on the variation of mutations in the groups’ DNA, the researchers were able to calculate the extent of the total population at different times. The results revealed a bottleneck between 930,000 and 813,000 years ago. During this period, the number of individuals fell to around 1280 – equivalent to a 99% loss of the population that had existed before this time.
We know from other research that the bottleneck coincides with a period of climate change when global temperatures plummeted and drought spread across Africa. The drought severely depleted the prey on which our ancestors depended, bringing them to the brink of extinction. The story of our species nearly came to an end before it had even begun.
So we are only here today thanks to a small and tough group of individuals. Who they were, what they looked like, we may never know — because of their small numbers, there is little chance of finding good fossils from them. But we carry their legacy with us – in the ancient mutations that we all hold in our cell nuclei.