With PCR, Pääbo started tackling a variety of ancient DNAs, honing his methods to one day track down the elusive Neanderthal. From ancient sloths to ancient mammoths, Pääbo recovered and read snippets of DNA for ancient species after ancient species. Pääbo even got bits and pieces of Neanderthal DNA from PCR, but not enough to understand what made modern humans different from our ancient comrade.
Finally in the mid-2000s came a breakthrough in DNA technology: high-throughput sequencing. High-throughput sequencing is like PCR on steroids. Imagine a person’s genetic blueprint as a book. Whereas PCR can make copies of a one or two pages from the book, high-throughput sequencing can make copies of every single page of the book all at the same time.
Using this technology, Pääbo finally read the first Neanderthal genetic blueprint in May 2010. And the treasures it held were well worth the 25-year wait.
Pääbo and his team compared the string of A’s, T’s, G’s and Cs in the Neanderthal blueprint to the blueprints of five living, breathing humans from around the globe. Stunningly, they found that 1-4% of modern humans’ DNA from Europe and Asia descends from Neanderthals, but Neanderthal DNA was noticeably missing in modern humans of African descent.
That left only one conclusion: Neanderthals and modern humans interbed during their time together.
Fast forward to December 2010. The DNA sequence from the Denisovan pinky bone blinks across Pääbo’s computer screen. He’s looking for similarities and differences with other hominins, trying to find just where in the tangled web this new human species fits … then, bingo!
The Denisovans are not only their own species, but they also interbred with modern ancient humans and with Neanderthals. And with that, the web of human evolution got a little more complicated and a little more clear.