The ancestral homeland of all humans alive today can be traced back to the south of the Zambezi River, in northern Botswana, scientists have said.
In a study published in the journal Nature, the researchers believe that they have, for the first time, been able to pinpoint the geographical location where the earliest ancestors of anatomically modern humans (Homo sapiens sapiens) arose 200,000 years ago.
Back then, this region – covering parts of Botswana, Namibia and Zimbabwe – was believed to be lush green and home to an enormous lake, allowing the ancestors to thrive for 70,000 years.
As the climate started to change, the population began to disperse – paving the way for modern humans to migrate out of Africa, and ultimately, across the world.
Read more about early humans:
Professor Vanessa Hayes, a geneticist at the Garvan Institute of Medical Research in Australia, said: “It has been clear for some time that anatomically modern humans appeared in Africa roughly 200,000 years ago.
“What has been long debated is the exact location of this emergence and subsequent dispersal of our earliest ancestors.”
Professor Hayes and her colleagues collected blood samples from study participants in Namibia and South Africa and looked at their mitochondrial DNA (mtDNA).
Professor Vanessa Hayes with a study participant in Namibia © Chris Bennett/Evolving Picture
As mtDNA is passed almost exclusively from mother to child through the egg cell, its sequence stays the same over generations, making it a useful tool for looking at maternal ancestry.
The team focused their research on the L0 lineage – modern human’s earliest known population – and compared the complete DNA code (mitogenome) from different individuals – including other sub lineages across various locations in Africa – to see how closely they were related.
The researchers then combined genetics with geology and climatic physics, to paint a picture of what the world looked like 200,000 years ago.
Geological evidence suggests the homeland region once housed Africa’s largest ever lake system, known as Lake Makgadikgadi.
And climate computer model simulations indicate that “the slow wobble of Earth’s axis” brought “periodic shifts in rainfall” across the region.
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.”
Prof Hayes concluded: “We observed significant genetic divergence in the modern humans’ earliest maternal sub-lineages that indicates our ancestors migrated out of the homeland between 130,000 and 110,000 years ago.
“The first migrants ventured north east, followed by a second wave of migrants who travelled south west.
“A third population remained in the homeland until today.”
However, many experts are critical of the study, especially with the suggestion that you can use modern genetic distributions to pinpoint exactly where humans lived some 200,000 years ago.
In a statement on Twitter, Prof Chris Stringer of the Natural History Museum, London suggests that the evolution of Homo sapiens is a more complicated process, and that “we are an amalgam of ancestry from different regions of Africa, with the addition of interbreeding from other human groups outside of the continent”.
Others have suggested the data is not robust enough to suggest a single point of origin.
Reader Q&A: Are we descended from Neanderthals?
Asked by: Ben Johnson, Glasgow
The Neanderthals lived in Europe and Asia from over 200,000 years ago until (in some areas) less than 30,000 years ago. If this question had been asked 20 years ago, the majority of experts would probably have answered yes, but new data and research have shown that our species Homo sapiens originated in Africa during the last 250,000 years from non-Neanderthal ancestors.
Our species spread from Africa during the last 60,000 years, and apparently replaced other human lines such as the Neanderthals. How this replacement happened – through conflict or competition – is still unclear, as is what happened when populations of our species encountered the Neanderthals.
Although I regard Homo neanderthalensis as a separate species – based on their distinctive anatomy – the Neanderthals were clearly closely related to us. Thus, as may occur with other closely-related species, interbreeding might have happened. Then the question takes on a different meaning, at a much finer level of resolution.
While we didn’t descend from the Neanderthals through an evolutionary transformation, if there was interbreeding, some of us today (particularly in Eurasia) might have Neanderthal-derived genes. However, my reading of the fossil and genetic data (the latter including some Neanderthal DNA) suggests that any Neanderthal contribution was vanishingly small. So I would still say that the answer, in any meaningful sense, is no.