New genetic study pinpoints humanity’s African ‘homeland’
All humans alive today are descended from a population of hunter gatherers that was sustained for tens of thousands of years in a small wetland in modern Botswana in southern Africa, according to new genomic research.
They abandoned this “homeland” when natural variations in the Earth’s orbit caused it to “wobble” and affect the climate, drying up the wetland into what is now part of the Kalahari Desert. At the same time, this climate change opened new green corridors through the desert that prompted the first human migration, first to the northeast, then southwest, and eventually all over the globe, according to the scientists behind the research published Monday in Nature.
Vanessa Hayes, a research geneticist from South Africa who works in Australia, said she recently flew over the Makgadikgadi Pans National Park, and marvelled at seeing tectonic fault lines in the dry earth, and salt pans that are the remnants of ancient lakes, now completely dry for 10,000 years.
Many years before that, however, around 200,000 years ago, modern humans first arrived in the region as the former Lake Makgadikgadi, then the largest in Africa, was breaking up into smaller lakes and wetlands.
It was a lush “oasis” surrounded by drier areas, she said, so it was a suitable habitat for modern humans and wildlife.
Tectonic activity had also created the Okavango Delta, which exists today, like a large trough taking in river water but giving it nowhere else to go other than evaporate.
Hayes said this area is a “homeland not a cradle.” This was not the beginning of Homo sapiens, the human species that descended from an ancient ape that shares a common ancestor with modern chimpanzees.
But it was a founder population, the one whose descendants made it out, and eventually everywhere.
The Australian and South African researchers came to this conclusion by overlaying genomic data from the maternal family tree of humanity with what is already known about human geography, linguistics, culture, history, and paleo archeology.
“Using that we could pinpoint what we believe is our human homeland,” Hayes said. “What we hadn’t known until this study is where exactly this homeland was.”
As they describe in the paper, there are two major branches on the tree that traces maternal human phylogenetics, or the study of genetic information passed down from mother to child.
That tree ultimately reaches back to Mitochondrial Eve, the name for the woman who was the most recent common ancestor of all humans living today in the lines of mother to child, in other words, everyone’s great-great-great … -grandmother.
One major branch of this tree is known as L3, which arose around the time anatomically modern humans left Africa, and is today shared by all non-african populations, and some but not all within Africa. The other is L0, the “rare deep-rooting” lineage that clusters in Southern Africa, where it originated, and where the research team was able to gather the mito-genome sequences of 198 southern Africans exhibiting L0. This predates the human migration from Africa, so offers a special window into the ancient past.
This research pushes back the estimated emergence of L0 to 200,000 years, which is in line with a broader trend in human-origins science that is pushing back the timing of the emergence of modern humans, once thought to have been as recent as 100,000 years or fewer.
For example, it was reported in 2017 that bones from a site called Jebel Irhoud in Morocco are as many as 350,000 years old, although this estimate is uncertain and there is likely no hereditary link from that human to humans living today.
There is also a pattern of ancient humans leaving Africa, becoming isolated, and eventually going extinct, but leaving a distinct fossil record. The famous “hobbits” whose remains were discovered in 2003 on the Island of Flores in Indonesia, known as Homo Floresiensis, are a notable example.
But for 70,000 years, this population around Lake Makgadikgadi, was sustained by a verdant homeland that was only disrupted by a changing climate caused by a quirk of the planet Earth’s orbital wobble.
From 200,000 to 130,000 years ago, the genomic study shows no new divergences, which Hayes said means the humans must have stayed in this region. The first divergence starts happening around 130,000 years, with that first lineage appearing to move northeast. Then at 110,000 years ago there is more splitting of the lineage, but going southwest.
This was the “first human exploration,” said co-author Axel Timmerman of the Center for Climate Physics in South Korea. He said the cause was a shift in the axis of the Earth’s orbit around the Sun.
These changes offered both a “push,” as the homeland dried up, and a “pull,” as new green corridors opened up.
“We propose that the southwest migrants maintained a successful coastal forager existence, while the northeast migrants gave rise to ancestral pastoral and farming populations,” the paper reads.
“Our results suggest that the greater Zambezi river basin, particularly the Kalahari region, had a significant role in shaping the emergence and prehistory of anatomically modern humans,” the Nature paper concludes.