Researchers sequenced the complete genomes of five southern Africans over the age of 80 including South African Archbishop Desmond Tutu and four Bushmen from Namibia
Archbishop Desmond Tutu has dedicated his life to the promotion of equality. Now a new study of his genetic makeup has helped scientists understand how different human beings are — at least genetically.
The genomes of Tutu and an indigenous Bushman from Namibia were decoded by an international team of more than 50 scientists for a study published this week in the journal Nature. Researchers also decoded partial genomes of three other Bushmen elders. The scientists discovered vast genetic differences between the men. In one case, two Bushmen who lived within walking distance of each other were genetically more diverse than a typical European and Asian are.
The authors said the diversity was no surprise, given that humans have lived in southern Africa for longer than anywhere else and have had some 200,000 years to develop genetic differences. "It is the cradle of mankind. If you are looking for the full range of human genetic variation, it's the place to look," says Stephan Schuster of Pennsylvania State University, the lead author of the study.
The study found 1.3 million genetic variations that had not been previously observed in studies of human DNA, which have until now focused mainly on European and Asian genomes. The variations described in the Nature paper should greatly aid scientists' quest to understand which genes increase susceptibility to disease or influence a patient's response to certain medications. The study of the latter phenomenon — known as pharmacogenomics — has thus far excluded southern Africans, who have not only been poorly represented in clinical drug trials but also, in many cases, fail to respond optimally to crucial medications for tuberculosis and HIV/AIDS, two major scourges of the continent. "We can now be more inclusive rather than exclusive and begin to redress the problem of certain drugs not working as well for [southern Africans] as [Europeans]," says Vanessa Hayes, a cancer specialist at the University of New South Wales and co-author of the study.
Further, because Tutu's medical records are already public — he is known to have had polio, prostate cancer and TB, all of which are influenced by genes — his genome will help scientists learn more about those diseases, Hayes says.
In a telephone press conference from Namibia, Hayes said the participants' advanced age (all were over 80) makes scientists confident that they are unlikely to carry rare genetic variations that lead to fatal disease, so they can focus on more subtle and common variations. Indeed, one of the participants, a Bushman hunter-gatherer known as !Gubi (the "!" expresses the palatal tick in his native language) was so robust that Hayes could not keep up with him in a rope-skipping competition.
All four hunter-gatherers had adaptive genetic variations, called single nucleotide polymorphisms, or SNPs, that may give them a survival advantage in the desert, researchers said: three men had two copies of variants associated with physical prowess and faster sprint performance, and one had a variant for a cellular mechanism that enables a person to retain salt and water — a benefit in a hot, dry climate. Yet another newly discovered genetic trait involved the ability to taste bitter chemicals, which could help hunter-gatherers avoid toxic plants.
Some scientists, most prominently the Harvard-based evolutionary biologist Steven Pinker, have publicly expressed concerns that such revelations of genetic differences may fuel wrongheaded beliefs that different racial and ethnic groups should be treated as inferior. During the telephone press conference, the authors were asked whether they shared this concern. Schuster said, "Overall, modern humans are very similar to one another." He reiterated that genetic diversity within Africa is greater than that between other continents.
Co-author Webb Miller of Pennsylvania State also noted that genetic diversity is a great boon to humanity because "if we didn't have this diversity we might be wiped out by the next major disease." And Hayes expressed frustration that Africans were considered "different" because they diverge from the European genome. "My question is what if the reference genome we used came from southern Africa? Then we would say the Europeans are different," she said.
For his part, Tutu was delighted at some of the unexpected discoveries from his genes. He is Bantu, a traditionally agricultural people, and was included in the study to represent their ancestry. But his genome revealed that he is also maternally related to the San, a hunter-gatherer population that has traditionally lived around the Kalahari Desert. "The fact that the test found that I am related to these wise people who paint rocks makes me feel very privileged and blessed," he told the BBC.
Tutu also made clear that although he has spent his life fighting apartheid and other manifestations of inequality, differences between people on the genetic level were not something that should threaten racial harmony. "It is exciting that science is finding evidence of genetic diversity among groups of people as well as among individuals, and this discovery should be embraced, not feared," he said. "It would be disastrous if scientists were to ignore the diversity of the human race, because this is the greatest asset of humanity."