Friday, November 01, 2019

Humanity's birthplace may be in Botswana or in several African locations

Researcher Vanessa Hayes with the Ju/’hoansi people in what is claimed to be the ancestral homeland of humanity. Chris Bennett/Evolving Picture

Makgadikgadi in Northern Botswana is one of the largest salt flats in the world and is all that remains of the formerly enormous Lake Makgadikgadi. Two hundred thousand years ago Makgadikgadi was Africa's biggest lake and it was surrounded by wetlands. Scientists from Australia's Garvan Institute of Medical Research and the University of Sydney in October published the results of DNA sequencing cross-referenced with other information, including geological and climate data. The scientists say that the area was completely surrounded by a very uninhabitable region, "which led to our hunter-gatherer ancestors staying put for some 70,000 years." The researchers claim that the area is the cradle of humanity.

In 2007 I published this article on Finfacts on the San people of the Kalahari Desert, and my own ancestral origins

Allan Wilson (1934-1991), a professor of molecular biology and biochemistry at the University of California Berkeley, had used a genetic approach to the study of evolution, which led to a theory that all humans descended from a single woman who lived in Africa 200,000 years ago. In 1987 Wilson and his colleagues published research that compared the mitochondrial DNA of women from five regions of the world. Mitochondrial DNA is inherited solely from one's mother, and the only intergenerational differences are those arising through random mutations. Wilson had discovered that human mitochondrial DNA mutates at a constant rate, and his team used this "molecular clock" to calculate the most recent common ancestor of the women studied.

Some scientists argue that modern humans did not evolve from a single population in a single location.

“I’m persuaded that southern Africa was an important area for human evolution,” says population geneticist Aylwyn Scally of the University of Cambridge, according to 'Science' magazine, published by the American Association for the Advancement of Science (AAAS). However, he says, studies of living people’s DNA can’t reveal the precise location of our ancestors. “It would be astonishing if all our genetic ancestry at this time arose in one small homeland.”

'Science' magazine notes that, "Modern humans arose in Africa at least 250,000 to 300,000 years ago, fossils and DNA reveal. But scientists have been unable to pinpoint a more specific homeland because the earliest Homo sapiens fossils are found across Africa, and ancient DNA from African fossils is scarce and not old enough."

Vanessa Hayes, University of Sydney on the latest research:

Where was the evolutionary birthplace of modern humans? The East African Great Rift Valley has long been the favoured contender – until today.

Our new research has used DNA to trace humanity’s earliest footsteps to a prehistoric wetland called Makgadikgadi-Okavango, south of the Great Zambezi River.

Our analysis, published in Nature, shows that the earliest population of modern humans (Homo sapiens sapiens) arose 200,000 years ago in an area that covers parts of modern-day Botswana, Namibia and Zimbabwe.

The left map shows the distribution of ancestral DNA among the sampled population. This allowed the ancestral homeland to be pinpointed to a region (shown on the right in pale orange) south of the Zambezi River, centred on northern Botswana. Chan et al., Nature 2019

Today it is a dry and dusty land with scattered salt pans, and it is hard to believe that modern humans lived and thrived in wetlands here for 70,000 years before our ancestors began to explore the rest of Africa, and ultimately the world.


Read more: 'Ancestors': a new game provides insights into how the first humans evolved


We pinpointed this region by studying mitochondrial DNA, known as the “mitogenome”. Unlike nuclear DNA, which is passed on by both mother and father, mitochondrial DNA is passed on only by the mother, which means it is not jumbled up in each generation.

If we think of all modern humans as occupying a particular place on a huge family tree, logically we should find the most diverse mitogenomes at the very base of the tree, because it is the ultimate source of all the various branches.

We already know that genetic data points to southern Africa as the cradle of humanity (unlike fossil evidence, most of which has been found in East Africa). But we wanted to refine our search still further, to pinpoint the exact location where humans first evolved.

To do this, we turned our attention to a group of people known as the KhoeSan. KhoeSan have the most diverse mitogenomes of anyone on Earth, which suggests their DNA most closely resembles that of our shared common ancestors. If we all sit on branches of the human family tree, then KhoeSan are the tree’s trunk.

Linguistically, KhoeSan people are click speakers, while culturally KhoeSan are foragers, with groups of San people still practising the old ways of life – hunting and gathering for subsistence.

Members of our research team have spent a decade working with KhoeSan communities, as well as people from other ethnicities and language groups, in Namibia and South Africa.

By generating mitogenome data for around 200 rare or newly discovered sub-branches of KhoeSan lineages, and merging them with all available data, we were able to zoom in on the very base of our evolutionary tree.

It is now clear our ancestors must have dispersed from a region south of the Zambezi River. This is consistent with geographical, archaeological and climate data, including the fact that this area would have been a fertile wetland at the time the first modern humans emerged.

Lush landscapes

Geological evidence suggests that at this time, the prehistoric Makgadikgadi lake that had dominated the region for millions of years had begun to break up through the shifting of the land. This would have created a vast wetland region, ideal to sustain life.

But if it was so ideal, why did our ancestors begin to explore other places between 130,000 and 110,000 years ago, first heading northeast and later southwest from the ancestral home?

Climate data suggests that at around that time the region experienced a huge drought. Notably, about 130,000 years ago humidity increased to the northeast of the homeland, and 110,000 years ago the same happened to the southwest. We speculate that this created passages of lush vegetation for our ancestors to leave the homeland, most likely following the game animals that were also forging into new regions.

According to Botswana Tourism on Makgadikgadi, "For much of the year, most of this desolate area remains waterless and extremely arid; and large mammals are thus absent. But during and following years of good rain, the two largest pans – Sowa to the east and Ntwetwe to the west – flood, attracting wildlife – zebra and wildebeest on the grassy plains – and most spectacularly flamingos at Sowa and Nata Sanctuary. Flamingo numbers can run into the tens – and sometimes – hundreds of thousands, and the spectacle can be completely overwhelming."

What’s more, our genetic data suggest the southerly migrants went on to inhabit the entire southern coast of Africa, with multiple sub-populations and huge population growth. Archaeological findings from the Blombos caves in South Africa have shown this region to be rich in evidence for cognitive human behaviour as early as 100,000 years ago. Again, we were amazed at how well we could match timeline data, crossing different yet complementary disciplines that have historically not worked together. This also allowed us to further speculate about the success of the southerly migrants being attributed to adapting their skills to the abundance of life in the oceans.


Read more: Ancient DNA is a powerful tool for studying the past – when archaeologists and geneticists work together


These earliest explorers left behind a homeland population, one that still remains within the ancestral lands today, having adapted to the much drier landscape. It has been a pleasure to spend the past decade engaging with the last descendants of humanity’s homeland, including the Ju/’hoansi people of the Kalahari in Namibia.

The Ju/’hoansi, who still practise their traditional way of life, are excited about our findings. They believe our study captures a history that they have told for generations by word of mouth alone. This is not only their story, but all of ours.The Conversation

Vanessa Hayes, professor, Garvan Institute of Medical Research and, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.