These salt pans in Botswana were once the Garden of Eden - scientists
Africa / 29 October 2019, 08:07am / COLIN FERNANDEZ SCIENCE CORRESPONDENT
A vast area of arid salt pans, it appears to be an unlikely Garden of Eden.
But Lake Makgadikgadi in northern Botswana is the spot where modern humans first evolved 200 000 years ago, according to researchers.
Back then, the area was a fertile wetland, alive with fish, shellfish and waterbirds, as well as mammals such as giraffes, lions and zebras.
Our ancestors settled there for 70,000 years, until the local climate changed, the researchers suggest.
They began to move on when fertile green corridors opened up around them, paving the way for future migrations out of Africa.
The assertion has triggered debate in scientific circles because not all experts believe the area is the cradle of humanity.
‘It has been clear for some time that anatomically modern humans appeared in Africa roughly 200,000 years ago,’ said Professor Vanessa Hayes who led the research. ‘What has been long debated is the exact location of this emergence and subsequent dispersal of our earliest ancestors.’
To locate the cradle of humanity, the team took samples of mitochondrial DNA from 1,217 Africans. Unlike nuclear DNA, a 50-50 mix of our mothers’ and fathers’ genes, mitochondrial DNA is only passed down from our mothers.
Professor Hayes, a geneticist at the Garvan Institute of Medical Research in Sydney, Australia, said: ‘Mitochondrial DNA acts like a time capsule of our ancestral mothers, accumulating changes slowly over generations.’ Comparing each individual’s different DNA code ‘provides information on how closely they are related’ and enables researchers to map their likely movements.
The researchers then combined genetics with geology and climatic physics, to paint a picture of what the world looked like at around 200,000BC.
Climate computer model simulations indicate that ‘the slow wobble of Earth’s axis’ brought ‘periodic shifts in rainfall’ across the region, encouraging dry surrounding areas to bloom.
Professor Axel Timmermann, a climate scientist at Pusan National University in South Korea, said: ‘These shifts in climate would have opened green, vegetated corridors, first 130,000 years ago to the north east, and then around 110,000 years ago to the south west, allowing our earliest ancestors to migrate away from the homeland for the first time.’
Few fossils remain in the harsh Lake Makgadikgadi area, though studies of pollen provide evidence of forest and grassland around it.
The authors stressed they ‘cannot rule out’ alternative explanations, but said their findings show that the lake area was ‘an ideal geographical locality’ for mankind’s sustained survival for 70,000 years.
Lake Makgadikgadi once covered an area about the size of Austria, but dried up several thousand years ago. Little now grows on the massive salt pans left behind, which are part of a national park, but there are areas of grassland.
While largely desert, a couple of years of good rains can create a temporary wetland, a magnet for wildlife, particularly flamingos.
Professor Chris Stringer, of the Natural History Museum voiced scepticism over whether mankind’s first ‘base’ has been found based on just one aspect of the genetic code. He said: ‘I’m cautious about using modern genetic distributions to infer exactly where ancestral populations were living 200,000 years ago, particularly in a continent as large and complex as Africa.
‘And, like so many other studies that concentrate on one small bit of the genome, or one region, or one stone tool industry, or one “critical” fossil, it cannot capture the full complexity of our origins.’
He said that another way of looking at DNA – focusing on the Y-chromosome – points in a different direction. ‘When we look at the male-inherited Y chromosome, the most divergent lineages currently known in extant humans are found in West Africa, not South Africa.’
He added that Swedish research by evolutionary scientist Carina Schlebusch and colleagues in 2017 presented ‘a much more complex picture’, adding: ‘These and many other data suggest we are an amalgam of ancestry from different regions of Africa.’