No intermarriage for 150,000 years for the Khoisan

They hunt with bows carved from wood, use short poisonous arrows, and speak in a click language that is the oldest human language in the world.

Now, an international team of scientists led by Singapore has proven that one of humanity's oldest "pristine" branches lies within the Southern African Khoisan people.

Since the birth of modern man some 200,000 years ago, a group of the Khoisan have married only within its tribes for the past 150,000 years, isolating itself genetically from the rest of the world.

The ground-breaking discovery upends conventional wisdom that all people today are the result of human groups mixing with one another over hundreds of thousands of years, said Nanyang Technological University's (NTU) Dr Stephan Schuster, who led the research.

"Khoisan hunter-gatherers in Southern Africa have always perceived themselves as the oldest people," he said.

The study, published in Nature Communications last week, makes it official, noted Dr Kim Hie Lim, an NTU senior research fellow.

The six scientists from Singapore, Brazil and the United States made the breakthrough after sequencing the genomes, or genetic make-up, of five living Khoisan tribesmen.

For two of them, the results were unlike anything seen in the DNA of Europeans, Asians and all other African ethnic groups.

Even after looking at the genomes of 1,462 people from 48 ethnic groups worldwide, the scientists found no evidence that these two Khoisan members' ancestors had mixed with any of the groups.

As for the other three Khoisan people whose genomes were not as pristine, Dr Schuster believes they must have had ancestors who married non-Khoisan neighbours, such as the nearby Bantu tribes.

This intermarrying between the non-Khoisan and Khoisan is believed to have occurred within only the last 3,000 years, based on recent genetic studies, he added.

According to the scientists, there are likely only about 100,000 people left whose pristine Khoisan lineage harks back 150,000 years, a minuscule fraction of the seven billion people globally.

But they will have an enormous impact on research into human history.

The high-quality genome sequences obtained from the Khoisan tribesmen will help researchers better understand human population history, especially that of understudied branches such as the Khoisan.

By comparing the genetic sequences of modern ethnic groups to those of the "pristine" Khoisan, for example, scientists can trace each group's ancestral lineage.

The genetic trail will also show when each group's ancestors intermarried with other tribes, and even the times when geographical migrations may have occurred over the centuries.

"The new data we gathered will also enable scientists to better understand how the human genome has evolved, and hopefully lead to more effective treatment options for some genetic diseases and illnesses," said Dr Schuster, who is a research director and professor of environmental genomics at NTU.

By studying the genetic diversity of Khoisan and non-Khoisan, and mapping the results to Earth's climate changes over the past 200,000 years, the scientists have already come up with several stunning conclusions.

The Khoisan, for example, likely made up the majority of living humans for most of the past 150,000 years, and did not cede that dominant position until as recently as 20,000 years ago, despite their numbers today.

Dr Kim said the Khoisan were also among the most genetically diverse people in the world. Despite looking similar to one another, some of them are as genetically different from one another as a European is from an Asian.

"This is despite the fact that they sometimes live within walking distance of one another," said Dr Schuster.

The analogy the scientists drew was that of a giant vat of jelly beans of different colours, which represents the original pool of humanity.

While groups of humans may migrate and spread farther and farther away from the source, each group that leaves will represent only a handful of jelly beans, and therefore never be as diverse as the vat's contents.

The Khoisan's diversity indicates that they made up the majority of living humans for a very long time, said the scientists.

Dr Schuster said the Khoisan likely lost their majority due to the decline and eventual end of the Ice Age between 22,000 and 12,000 years ago.

Then, global warming likely made new areas hospitable so people flourished there, while the stationary Khoisan maintained their population.

"When people today talk about the extinction of species, they usually talk about plants and animals," said Dr Schuster.

"But this shows that we, modern people, flourished only because of a quirk in climate change. If the situation reverses or there is another quirk, we could easily become targets for extinction ourselves."

The researchers said they will look for other people, possibly in South Asia and South America where there are "uncontacted" tribes, who could have similarly pristine lineages, as they may have reproduced strictly among themselves since leaving Africa some 75,000 years ago.

Said Dr Kim: "Since our study has found such people who did not inter-marry, there might be more of such unique individuals in other parts of the world, and their genome information can disclose history we do not know yet."

zengkun@sph.com.sg

'Bushman royal bloodline'

Remember The Gods Must Be Crazy, the hit movie series in the 1980s and 1990s?

It turns out that some of the Ju/'hoansi tribe members who acted in the series may have one of humanity's most ancient "pristine" lineages.

An international team of scientists led by Dr Stephan Schuster of Nanyang Technological University (NTU) made this discovery when they sequenced the genomes of five Southern African Khoisan people, which included two from the Ju/'hoansi tribe.

They found that, for the past 150,000 years, some of the Khoisan married and had children only among themselves, keeping their lineages pristine.

"I sometimes think of them as a 'bushman royal bloodline'," said Dr Schuster with a smile.

The German national had conducted field work for the discovery from 2008 to 2010 with just one fellow researcher, Dr Vanessa Hayes of the Garven Institute of Medical Research in Sydney, Australia.

Dr Schuster said: "Dr Hayes was from Cape Town in South Africa, and like many people living in the area she was always fascinated by the bushmen, like the Khoisan, who are still practising the hunter-gatherer lifestyle."

Over the three years, the pair contacted the Ministry of Health in Namibia, sought permission to collect the bushmen's genetic data, and eventually went into the bushland themselves.

"We rented a vehicle and went for days and days and days through the bush, getting help from church organisations, locals, farmers, everybody." All of them wanted to help, "to show how special the Khoisan were".

The tribe's native language - the oldest in human history - consists of five clicking sounds. But the elders also spoke Afrikaans, which they had learnt from serving in the South African army. Dr Hayes, who also spoke Afrikaans, was able to converse with them.

"They said 'Study us. We are the oldest people, we want to show the others we were here first'," said Dr Schuster.

The Khoisan, as it turned out, had a low social status among the 28 ethnicities in Namibia, as they were physically smaller and do not own property.

Dr Schuster said the research showed that the Khoisan bushmen should be given land so they have the opportunity to maintain their lifestyle, thereby preserving an important part of human history.

"If we lose these people, we lose our own diversity. In 50 years, they may be all gone."

Ancient man, modern man

Bushman's height: 140cm.

Schuster's height: 186cm.

Bushman's vision: Can see the moons of Saturn at night with bare eyes.

Schuster's vision: Has to wear contact lenses or spectacles.

Bushman's hearing: Can hear airplane 60km away, even in old age.

Schuster's hearing: Has extremely good hearing but cannot hear airplanes 60km away.

Bushman: Can live for up to 11 days without drinking water.

Schuster: Can live up to three days without drinking but will die afterwards

Bushman: Speaks oldest human language with five clicking sounds, and Afrikaans, the language spoken mainly in South Africa and Namibia.

Schuster: Speaks English, German and Italian.

Bushman: Stores fat in his buttocks in times of plenty. Can then completely consume body fat and go back to being skinny.

Schuster: Stores fat in belly.

Bushman: Can detect very faint traces of poison in plants and detoxifies poisons from the body very quickly. Can eat many plants in nature.

Schuster: Eats chicken rice.

Bushman: Can walk for several days in hot desert without water, and outlast antelope prey.

Schuster: Needs soda and chicken rice all the time.

This article was first published on December 8, 2014. Get a copy of The Straits Times or go to straitstimes.com for more stories.