He has won the Nobel Peace Prize, campaigned for human rights and bared his soul in truth and reconciliation. Now Desmond Tutu has given something else to humanity: his genome.
Archbishop Tutu, 78, has allowed scientists to decode his entire genetic makeup and to post it on the internet as part of a project to document the immense variety of DNA sequences that constitute the human species.
Tutu was chosen because he is a typical ethnic representative of the majority South African population who speak one of the Bantu group of languages.
His genome was decoded along with those of three other southern Africans belonging to the Kalahari Desert Bushmen, or San people.
Whereas Bantu South Africans migrated to southern Africa over the course of many centuries from their original homeland of west Africa, the Bushmen of the Kalahari are believed to have lived in the region for tens of thousands of years – so they represent one of the oldest-living distinct groups of human beings.
Scientists said that a comparison of the full genomes shows the enormous range of genetic diversity that exists on the continent. Interestingly, the study, published in the journal Nature, found that on average there is more genetic diversity between the southern Africans than there is between typical non-Africans from different parts of the world. This genetic diversity of Africans is testament to the continent’s long period of human evolution, scientists said.
“The indigenous hunter-gatherer peoples of southern Africa are believed to be the oldest known lineage of modern humans. On average, we found as many genetic differences between two Bushmen, than between a European and an Asian,” said Vanessa Hayes if the University of New South Wales, a co-leader of the study.
“This research now provides us with the tools to read the story of human evolution and specifically the story of disease evolution. It has been well established that the African continent is the cradle of civilisation and therefore the origin of disease, we just haven’t known to what extent,” Dr Hayes said.
“Human variation is vital in determining disease risk and drug response for complex genetic diseases. It is important to include genetic differences from all global populations in research efforts,” she said.
Through his Tswana and Nguni tribal ancestry, Archbishop Tutu was an ideal representative of most southern Africans belonging to the Bantu-language group, Dr Hayes added.
The study identified 1.3 million genetic variants in the sequence of 3 billion “letters” of the human genome that had not been previously observed. “To know how genes affect health, we need to see the full range of human genetic variation, and southern Africa is the place to look,” Dr Hayes said.
This variety shows that southern Africans are quite distinct genetically from Europeans, Asians and west Africans. One of Kalahari Bushmen possessed more novel genetic variations in his genome than any other fully-sequenced human genome.
One aim of the study is to identify genetic variations that may have come about as a result of living a hunter-gatherer way of life in the desert, such as the Bushmen,
or pursuing an agricultural way of life, such as the Bantu-speaking peoples.
“The availability of Bushmen and southern African Bantu genomes permits researchers to examine one of the few remaining instances in the world of coexisting foraging and farming groups,” said Professor Stephen Schuster of Penn State University, the second co-leading of the team.
One of the bushmen, for instance, has a gene controlling changes to a microscopic pore in the membrane of the cell that allows salt ions to flow in and out. The mutation is an advantage in a dry environment because it enables the person to retain salt and water.
The Bushmen genome also appears to lack the genetic mutations that allow individuals to digest milk in adulthood – mutations that are thought to have arose as a result of cattle rearing – as well as the genetic variations thought to protect against malaria.
“These physiological and genetic differences may guide future studies into the much debated question of whether population replacement, rather than cultural exchange, has driven the expansion of agriculture in southern regions of Africa, as was observed for last Stone Age populations in Europe,” the scientists said.