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.
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