A team of scientists reported on Thursday that it had recovered the genome from a 4,500-year-old human skeleton in Ethiopia — the first time a complete assemblage of DNA has been retrieved from an ancient human in Africa.
The DNA of the Ethiopian fossil is strikingly different from that of living Africans. Writing in the journal Science, the researchers conclude that people from the Near East spread into Africa 3,000 years ago. In later generations, their DNA ended up scattered across the continent.
“It’s a major milestone for the field,” said Joseph Pickrell, an expert on ancient DNA at the New York Genome Center who was not involved in the study. For decades, scientists had doubted that ancient DNA could survive in the tropics. The study raises hopes that scientists can recover far older human genomes from Africa — perhaps dating back a million years or more.
“I would bet it’s not that far in the future,” said Lee Berger, a paleoanthropologist at the University of the Witwatersrand who recently announced the discovery of an ancient humanlike species called Homo naledi.
In the 1980s, few scientists would have believed it possible to reconstruct an entire genome from the DNA in a fossil. Once a human or other animal dies, its DNA starts to fall apart. Bacteria swiftly colonize the corpse, overwhelming it with their own DNA.
But by the 1990s scientists were beginning to retrieve fragments of DNA and piece them together into longer segments. In 2010, researchers assembled the genome of a Neanderthal from 38,000-year-old fossils from Croatia. In many other cases, researchers failed to find ancient DNA in human fossils. Because it was widely suspected that the heat and humidity in the tropics would destroy genetic material, many scientists flocked to places like Siberia to seek ancient DNA.
That skepticism proved to be unwarranted. In recent years, Ron Pinhasi, an archaeologist at University College Dublin, and his colleagues have been surveying different bones to see if any are particularly good for preserving DNA. They found that the bone surrounding the inner ear can hold an abundance of genetic material even when other bones have lost theirs.