Mapping our roots

JON CRAIG CANAVAN spoke to the woman who is unravelling the secrets of our past.

Every gene has a story to tell. The human gene can reveal more than whether you are going to have blue eyes or red hair, be tall or short, big-boned or petite, black, white or bright pink - the human gene is like a history book that can spill the beans about where we as a species come from.

But it's a book that is written in a language unfathomable to many and to understand it we need a translator of uncommon brilliance and understanding, a translator like Professor Himla Soodyall, the pint-sized but massively influential director of the Human Genomic Diversity and Disease Research Unit.

The unit, jointly run by the Medical Research Council, the National Health Laboratory Service and the University of the Witwatersrand, is based at the National Health Laboratory Service's headquarters on the edge of downtown Johannesburg. Its graceful old buildings bely the fact that some of the most important research into the origins of human beings is taking place behind its faded brownstone walls.

The key person behind that research is Prof Soodyall, who describes her work as 'focusing on the value of incorporating population history when mapping and modelling human genetic variation in health and disease.

'More specifically, we are interested in explaining the demographic and evolutionary processes responsible for producing the complex patterns of variation in southern African populations.

'Several factors contribute to producing changes or mutations in the genome. These changes leave imprints in the form of altered gene frequencies, which are called gene markers.

'At the research unit, we use several types of genetic markers to examine the genetic structure of southern African and Malagasy populations. When this research is used in conjunction with the findings of archaeologists, linguists, anthropologists and historians, it contributes to our knowledge of the history of the people of Africa and, in the broader perspective, the world,' she says.

'The research has many medical benefits - it allows researchers to map the evolution of disease in various populations and helps us to understand why one group of people are more susceptible to a particular disorder than another. In the end, though, we are researching the evolutionary history of our species.

'Genetic data should be considered as another "tool" to study history,' says Prof Soodyall. 'Unlike some of the other lines of evidence, the evidence in the genes is the direct result of our inheritance and is transmitted from one generation to the next in an unbiased way.

'I'm not saying that genetics is the only discipline that should be used in the study of human history. The evolution of humans can be reconstructed using a variety of methods, each having its own strengths and limitations. In trying to understand the complex patterns of genetic variations among different population groups, we have to use genetic data in conjunction with information gleaned from other disciplines - linguistics, anthropology and archaeology all have a role to play,' she says.

'But genetic approaches to addressing questions of anthropological interest have made, and will continue to make, a significant contribution toward the knowledge of our history as a species.'

Although her speciality is the mutational history of mitochondrial DNA (the DNA we inherit only from our mothers) Prof Soodyall has immersed herself in all the disciplines mentioned above, all to better understand human history. And despite the immediate medical benefits of her research to the public, it is the history of the human species that most concerns her.

'As I became more immersed in the research, from when I first started my work on mitochondrial DNA, a story developed in my mind and I want to tell that story: the story of our species.'

In researching that story Prof Soodyall has studied the mitochondrial DNA of thousands of people from all over the world, pouring over the variations in their genetic sequences like a woman possessed, eventually determining that the Bushmen of southern Africa carry some of the oldest mitochondrial mutations in the modern world.

These mutations have been passed on from generation to generation among the Bushmen for more than 100 000 years. It is clear proof, she says, that modern humans appeared first in Africa, where the oldest mutations and the most genetic diversity exist to this day.

'The base of human genetic diversity was established in Africa,' explains Prof Soodyall. 'At some point in the past a group of people who carried just a subset of that diversity left Africa, and they gave rise to all of the populations that we see today outside of Africa. And every time we add more data to this theory, it makes more sense.

'This sort of data has the potential to abolish racism. Race is purely circumstantial, like hair or eye colour. But it establishes a social hierarchy that people can use to exploit others, a hierarchy that has no basis in biology.'

For Prof Soodyall, genetics is very much about identity.

'If we know where we come from, we may be able to understand who we are. And if we know where we have come from, we might just discover where it is we are going. 'If we use the genetics to illuminate the history of the human species we can say “ look, we are one people.” We can make the concept of racism obsolete. Ultimately the differences that you see in people are minor changes that have taken place in a very short space of time. We are one people, one species, all from the same tree of evolution.'