by STEVEN MITHEN
IMAGE/Just Science
Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past by David Reich, Oxford, 368 pp.
A scientific revolution is underway in the way we investigate and understand the past. The extraction and analysis of ancient DNA from human skeletal remains, the field in which David Reich is a leading researcher, is a technical advance that eclipses the advent of radiocarbon dating in the 1950s, and is already transforming our knowledge, not only of human biological evolution, but also of human history and culture.
The potential value of genetic insights into the past became clear in 1987 when Allan Wilson and his colleagues at Berkeley sampled mitochondrial DNA (mtDNA) – a mere 0.0005 per cent of the genome, inherited solely from mother to daughter – from living populations and analysed it to show that Homo sapiens, rather than having a multi-regional origin, evolved in Africa 200,000 years ago or later, then dispersed throughout the world, displacing existing populations. Seizing the moment, the geneticist Luigi Luca Cavalli-Sforza produced The History and Geography of Human Genes (1994), in which he sought to synthesise archaeology, history, linguistics and genetics to tell the story of human migration and describe the way the world’s populations became established. Reich thinks this was a visionary work but flawed, not just because of the paucity of genetic evidence available at the time but also because Cavalli-Sforza didn’t sufficiently appreciate the sheer complexity of past population movements. These could only be revealed by ancient, not modern, DNA.
It was Svante Pääbo and his colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig who developed much of the technology for extracting DNA from ancient skeletal remains. Pääbo’s group were primarily concerned with the Neanderthals. At first they focused on extracting mtDNA, partly because its relative abundance increased the chances of successful extraction, and partly because of the frequency of mutations in this part of the genome, all the better to establish the point of separation of the Neanderthals from the modern human lineage. The problem with mtDNA is that since it tracks just a single female lineage, it provides only an extremely narrow window through which to view the past: the evidence is incomplete, and potentially misleading. The real prize was to extract the complete Neanderthal genome. By 2007, armed with dramatically increased computing power and bones containing organic material with well-preserved DNA, Pääbo was in a position to begin developing a method for whole-genome extraction. He brought together an international team, which included David Reich.
London Review of Books for more