A study published in the journal Nature says a large ancient wetlands region spanning modern-day northern Botswana represents the ancestral homeland of all of the 7.7 billion people on Earth today.

Their study, guided by maternal DNA data from more than 1,200 people indigenous to southern Africa, proposed a central role for this region in the early history of humankind starting 200,000 years ago, nurturing our species for 70,000 years before climate changes paved the way for the first migrations.

The area in question is now dominated by desert and salt plains.  But scientists say at one time northern Botswana housed Africa's largest lake. The lake was twice the area of today's Lake Victoria and gave rise to the ancient wetlands covering the Greater Zambezi River Basin that includes northern Botswana into Namibia to the west and Zimbabwe to the east.

It has been long established that Homo sapiens originated somewhere in Africa before later spreading worldwide.

"But what we hadn't known until this study was where exactly this homeland was," said geneticist Vanessa Hayes of the Garvan Institute of Medical Research and University of Sydney, who led the study published in the journal Nature.

The oldest-known Homo sapiens fossil evidence dates back more than 300,000 years from Morocco. The new study suggests that early members of our species as represented by the Morocco remains may not have left any ancestors living today, the researchers said.

"There is no contradiction between the presence of an early Homo sapiens-like skull in northern Africa, which may be from an extinct lineage, and the proposed southern African origin of the Homo sapiens lineages that are still alive," added study co-author Axel Timmermann, a climate physicist at Pusan National University in South Korea.

However, some researchers were not convinced by the study's findings.

Chris Stringer, who researches human evolution at the Natural History Museum in the UK, says the study of human origins is complex.

"I am very 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," he said in a statement posted on Twitter.

"Moreover, like so many 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 mosaic origins, once other data are considered," he said.

He noted that other studies have suggested that our origins may be linked to West Africa and East Africa, not Southern Africa.