The Elephant Family Tree, Extinct and Extant

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Are you getting impatient for scientists to resurrect an extinct species? Me, too. Jurassic Park popularized the idea that ancient DNA could be used to reanimate dinosaurs. The cloning of Dolly the sheep provided a plausible mechanism, and the discovery of soft tissue in dinosaur bones and the recovery of still-meaty mammoth fossils in Siberia made the possibility even more tantalizing.

But while we wait, the study of ancient DNA has led to some surprising discoveries. It's not exactly routine to recover genetic material from an extinct species, but there is a standard method. It's been used to reveal the evolutionary history and family trees of extinct species such as the dodo (its distant relative, somewhat disappointingly, is the pigeon) and to track the population decline of the cave bear to understand why it went extinct. Svante Paabo is pretty much the king of ancient hominid DNA; his team recently reported that a previously unknown species of hominid, the Denisovans, lived alongside Neanderthals and modern humans in Asia tens of thousands of years ago. If the discovery holds up, it will be the first species designation based more on DNA than on bones.

Now scientists have used DNA from an extinct animal to better understand living species: the elephants. You'd think there wouldn't be much left to learn about a species that big and conspicuous, but people are still discovering new behaviors in some elephant groups, such as unexpected bonding among males. One longstanding question is just how many elephant species there are, and a genetic study incorporating DNA from woolly mammoths reveals one additional branch in the family tree.

Mitochondrial DNA studies had suggested that woolly mammoths and Asian elephants are closely related, but the new work was possible because the researchers made the most complete reconstruction ever of mammoth nuclear DNA (that is, the stuff you'd need to clone a mammoth, ahem). (They tried to analyze DNA from American mastodons as well, but that species is older and more distantly related to today's elephants, and the DNA was too incomplete for the analysis.) The new study showed that woolly mammoths are Asian elephants' closest relatives—closer even than African elephants.

Even more surprising was the discovery that, according to DNA, African forest elephants and African savanna elephants, sometimes considered two populations of the same species, are two separate species as far removed from each other in evolutionary time as are Asian elephants and woolly mammoths.

The authors are just beginning to figure out what these patterns reveal about ancient ecosystems: what was the geographic or biological boundary between forest and savanna elephants? Can male dispersal explain some of the patterns in the DNA? But in the meantime, it's somehow satisfying to know that woolly mammoths were so closely related to a living, trumpeting species. That's got to make them even easier to clone, right?


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