The Sixth Extinction: An Unnatural History

over the floor.
Pääbo, who is Swedish, is sometimes called the “father of
paleogenetics.” He more or less invented the study of ancient DNA. His
early work, as a graduate student, involved trying to extract genetic
information from the flesh of Egyptian mummies. (He wanted to know
who among the pharaohs was related to whom.) Later, he turned his
attention to Tasmanian tigers and to giant ground sloths. He extracted
DNA from the bones of mammoths and moas. All of these projects were
groundbreaking at the time, yet all could be seen as just warm-up
exercises for Pääbo’s current, most extravagantly ambitious endeavor:
sequencing the entire Neanderthal genome.
Pääbo announced the project in 2006, just in time for the 150th
anniversary of the original Neanderthal’s discovery. By then, a complete
version of the human genome had already been published. So, too, had
versions of the chimpanzee, mouse, and rat genomes. But humans,
chimps, mice, and rats are, of course, living organisms. Sequencing the
dead is a whole lot more difficult. When an organism expires, its genetic
material begins to break down, so that instead of long strands of DNA,
what’s left, under the best of circumstances, are fragments. Trying to
figure out how all the fragments fit together might be compared to trying
to reassemble a Manhattan telephone book from pages that have been put
through a shredder, mixed with yesterday’s trash, and left to rot in a
landfill.
When the project is completed, it should be possible to lay the human
genome and the Neanderthal genome side by side and identify, base pair
by base pair, exactly where they diverge. Neanderthals were extremely
similar to modern humans; probably they were our very closest relatives.
And yet clearly they were not humans. Somewhere in our DNA must lie
the key mutation (or, more probably, mutations) that set us apart—the
mutations that make us the sort of creature that could wipe out its
nearest relative, then dig up its bones and reassemble its genome.
“I want to know what changed in fully modern humans, compared