Scientists have pinpointed a fertile river valley in northern Botswana as the ancestral home of all human beings.

The earliest anatomically modern humans (Homo sapiens) arose 200,000 years ago in a vast wetland south of the Zambezi river which was the cradle of all mankind, a new study has revealed.

This lush region – which also covered parts of Namibia and Zimbabwe – was home to an enormous lake which sustained our ancestors for 70,000 years, according to the paper published in the Journal Nature.

Between 110,000 and 130,000 years ago, the climate started to change and fertile corridors opened up out of this valley. For the first time, the population began to disperse – paving the way for modern humans to migrate out of Africa, and ultimately, across the world.

Lead researcher 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).

As mtDNA is passed almost exclusively from mother to child through the egg cell and 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. They also looked at 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 which was double the size of modern Lake Victoria.

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 northeast, and then around 110,000 years ago to the southwest, allowing our earliest ancestors to migrate away from the homeland for the first time.”

Professor Hayes said: “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 northeast, followed by a second wave of migrants who travelled southwest. A third population remained in the homeland until today.”

Researchers believe that the humans who migrated southwest flourished and experienced steady population growth. They say this could be due to an adaptation to marine foraging.

“These first migrants left behind a homeland population,” said Professor Hayes.

“Eventually adapting to the drying lands, maternal descendants of the homeland population can be found in the greater Kalahari region today.”