Pääbo, who founded the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, pioneered methods for sequencing ancient DNA in 1990 by attempting to sequence the mitochondria of Neanderthals, the energy powerhouses of cells. He accomplished this by utilizing a 40,000-year-old Neanderthal bone.
Because DNA degrades and can get polluted, it was assumed that sequencing ancient DNA would be difficult.
"Humanity has always been fascinated by its origins," remarked Anna Wedell, head of the Nobel Committee for Physiology or Medicine, at the announcement of the prize on October 3. "How did we get here?" And how do we fit in with those who came before us? "What distinguishes us from extinct early humans?"
"Pääbo ultimately accomplished the [then-thought-impossible] sequencing and assembly of the Neanderthal genome... "By analyzing and comparing genomic sequences, we identified an altogether new hominid [the Denisovans]," she explained.
Because mitochondrial DNA contains relatively little information about a person's overall physiology, Pääbo analyzed ancient DNA contained in the nucleus, or major control center, of ancient cells.
Pääbo sequenced the Neanderthal genome using three Neanderthal bone specimens from Croatia's Vindija cave, as well as others from Germany, Russia, and Spain.
Pääbo discovered that these hominid groups separated about 400,000 to 800,000 years ago and would have bred with each other in western Eurasia after H. sapiens came out of Africa around 70,000 years ago by comparing the Neanderthal DNA with that of Homo sapiens.
As a result, up to 2% of the DNA in people of European or Asian heritage is derived from Neanderthals, including genes involved in our immunological response to infections.
Pääbo analyzed DNA from a 40,000-year-old finger bone found in a cave in southern Siberia in 2008. He found a new form of hominid, the Denisovans, by comparing this DNA to that of both Neanderthals and H. sapiens.
"He was stunned, quite thrilled," said Thomas Perlmann, secretary of the Nobel Assembly, describing the moment Pääbo was informed of his Nobel achievement.