This year’s first Nobel laureate sequenced the DNA of Neanderthals

The first Nobel prize to be announced each year is often referred to as the “Nobel prize for medicine”. But that is not its real name. It is actually the prize for “physiology or medicine”. And this year’s award was firmly on the physiological side of the divide. The winner—and there was only one, rather than the usual two or three—was Svante Paabo, a man who has the rare distinction of having invented an entire scientific discipline, palaeogenomics, more or less by himself.

Palaeogenomics is the study of the genomes of ancient, often extinct, biological species. In particular, Dr Paabo concentrated on ancient members of the genus Homo. His early work, going back to 1985, was on Egyptian mummies. Mummification in Egypt began about 4,600 years ago—an eyeblink in palaeontological terms—and the desert climate of that country is particularly conducive to the preservation of DNA. So this was a good place to begin. But gradually, as genetic-sequencing techniques improved, he was able to push backward in time.

His first big breakthrough came in 1997, when he sequenced the mitochondrial DNA of Neanderthals, a species of human that lived in Europe and western Asia, and became extinct about 30,000 years ago. A cell’s mitochondria are its power packs, extracting energy from glucose and transferring it to a molecule called ATP, which is then used to drive metabolic reactions. Because they derive originally from bacteria that became symbiotic about 2bn years ago with cells ancestral to animals, plants and so on, mitochondria have their own DNA, separate from that in a cell’s nucleus. And because there are lots of them in a cell, whereas there is only one nucleus, their DNA is much more abundant, and therefore more likely to survive in detectable quantities.

Dr Paabo’s analysis showed that Neanderthal mitochondrial DNA is indeed different from that of Homo sapiens, and allowed, through estimates based on how quickly such DNA evolves, an estimate (800,000 years ago) of when the two species diverged. The real prize, however, came in 2009, when he and his colleagues at the Max Planck Institute for Evolutionary Anthropology, in Leipzig, Germany, which he helped to found, announced a sequence of the nuclear DNA of Neanderthals—for technological improvements meant that the definition of “detectable quantities” had by then changed. That, together with successor sequences, has permitted the compilation of a catalogue of genes found in Homo sapiens but not Homo neanderthalensis. And within that catalogue, presumably, lies the explanation, not yet elucidated, of what makes Homo sapiens such an extraordinary species.

The biggest surprise of Dr Paabo’s career, though, was probably the identification, purely from its DNA, of an entire, new species, Homo denisova. The original genome of this was extracted from a finger bone found in a cave in the Altai mountains of Russia. Denisovans were related more closely to Neanderthals than to Homo sapiens, and subsequent analysis has shown that the two sometimes interbred. More relevant from a modern perspective, though, is that both also interbred with Homo sapiens when that African species began turning up in their European and Asiatic homelands 70,000 years or so ago. The traces are there to this day, with modern Europeans having 1-2% of Neanderthal DNA and some people in Asia and Australasia up to 6% of Denisovan DNA.

Dr Paabo’s career is, then, a tour de force of scientific detection. And there is one other thing. Though he spent much of his career in Germany, he is Swedish. Alfred Nobel’s will specified, “It is my express wish that when awarding the prizes, no consideration be given to nationality, but that the prize be awarded to the worthiest person, whether or not they are Scandinavian.” It was, nevertheless, hard not to notice a slight swelling of patriotic pride when Thomas Perlmann, secretary of the Karolinska Institute’s Nobel Assembly, read out the announcement. ■