Tutu part Bushman, DNA shows
Johannesburg - Researchers have sequenced the full genome, or entire genetic material, of Archbishop Emeritus Desmond Tutu as part of a two-year study of five Africans aimed at shedding light on the genetic make-up of southern Africans.
The results of the study, which was conducted by researchers from universities in the United States, Australia and South Africa, have been published in this week's issue of Nature magazine.
Tutu, 78, who is of Bantu or pastoralist ancestry, and an elderly San man from Namibia, had their full genomes mapped, while partial sequencing was carried out on DNA from another three Bushmen.
The Khoi, San, or Bushmen as they are variably called, are the indigenous peoples of southern Africa and, genetically speaking, the oldest race on earth.
The study, which was led by researchers from Pennsylvania State University in the US and the University of New South Wales, Australia, showed the Bushmen to be genetically very divergent not only from other humans, but also among themselves.
"In terms of nucleotide substitutions, the Bushmen seem to be, on average, more different from each other than, for example, a European and an Asian," the researchers found.
By including Tutu the researchers were able to compare the Bushmen's genomes with that of a person who is more representative of southern Africans, genetically speaking, Vanessa Hayes, group leader of cancer genetics at the University of New South Wales and Children's Cancer Institute Australia told the German Press Agency dpa.
Tutu has both Sotho-Tswana and Nguni ancestry. Between them, these two language groups cover most people in southern Africa.
Tutu, who received the Nobel Peace Prize in 1984 for his peaceful resistance to the then apartheid regime in South Africa, is also a survivor of prostrate cancer, tuberculosis and polio - a factor that added to his suitability because the results of the study will also be used in medical research.
Prostrate cancer has a high prevalence rate in Africa.
"For me The Arch was the obvious choice," Hayes said.
"He completely got it! He was very willing to participate."
Among their findings, the researchers noted that the five Bushmen between them showed 1.3 million novel DNA differences genome-wide, including 13 146 amino acid variants.
The researchers also discovered that none of them had any of the alleles - the alternative form of a gene - that makes people of Bantu ancestry more resistant to malaria and makes the adults lactose tolerant.
These genetic changes in people of Bantu ancestry are believed to have developed in response to their cattle-rearing lifestyle.
As the Bushmen become increasingly sedentarised, the absence of such alleles could make them vulnerable to certain diseases and conditions, Hayes said, adding further research would be necessary to fully understand the implications.
Finally, the results threw up a surprise for the bishop, who has discovered he has Bushman ancestry.
Tutu's mitochondrial DNA, a part of a person's DNA make-up that is inherited from the mother and is separate from chromosomal DNA, comes from the Bushmen.
"He's excited about it," said Hayes. "He said 'I'm truly an individual from southern Africa. I'm a true descendant of the first person'."
Tutu is the second Nobel laureate to have his genome sequenced after James Watson, who was a co-discoverer of the structure of DNA.
Genome sequencing is a lengthy, expensive process. To date around 25 people have had their full genetic material detailed.
On Thursday, Tutu and the Bushmen community are to be formally presented with the results in a ceremony in the presence of political leaders and academics in the Namibian capital Windhoek.