Ultima Thule

In ancient times the northernmost region of the habitable world - hence, any distant, unknown or mysterious land.

Saturday, April 22, 2006

Bringing Back the Brontosaurus

By Aussiegirl

Shades of Jurassic Park! It looks like such sci-fi science is getting closer and closer. I like the fatherly warning of the last paragraph: And even if we could re-create, say, a bronto­saurus, it would be plunked down in a place where it didn't belong and where it would have no adults to teach it how to be a proper brontosaurus.

Wired 14.04: Bringing Back the Brontosaurus

Bringing Back the Brontosaurus

Digging for fossils is for dinosaurs. Today's animal trackers are using genomics to reconstruct - and one day resurrect - the original hot-blooded beast.

By Steve Olson

About 100 million years ago, a creature the size of an opossum ambled through the forests of what is now South America. It was probably a ratlike thing, with coarse fur, a scrawny tail, and furtive eyes. If you went back in time with a .22, you could pick it off with one well-aimed shot. But that wouldn't be a good idea. That creature was your ancestor.

Over millions of years, an evolutionary cornucopia spilled from that unassuming ur-mammal. The species to which it belonged split into two daughter species, and then those species split, and the process repeated again and again. One line eventually led to rabbits, beavers, and mice. The members of another line began hunting in shallow bodies of water and gradually evolved into whales and dolphins. Meanwhile, with a few exceptions, the other mammals living back then - and their descendants - eventually went extinct. [....]

Biologists have been drawing diagrams like these since Charles Darwin sketched the first evolutionary tree in 1837. But Haussler's reconstruction process is ­different. Instead of examining fossils and tracing a line from extinct creatures down to those alive today, he's trying to move back up the evolutionary tree. Haussler is attempting to run evolution in reverse.

He starts by comparing the genomes of humans and other existing animals with one another, making inferences about the DNA sequences in their common ancestors. Haussler has used this technique to mathematically reassemble parts of the genome of the progenitor of chimps and humans - a shambling, hirsute, apelike creature that lived about 6 million years ago. He has reconstructed DNA sequences of the predecessor of most hoofed animals, an unprepossessing beast that had to dodge the footfalls of dinosaurs to survive. Most audaciously, Haussler and his collaborators have pieced together much of the genome of the ur-mammal itself, which they plan to release in draft form later this year. [....]

Wait a minute. Wasn't all this "ancient DNA" talk pretty well trashed after Jurassic Park? When an animal dies, DNA starts to break down like a cigar left in the rain, and, after the movie came out, ­scientists showed that amber-encased mosquitoes would never be able to provide enough dinosaur DNA to re-create a T. rex.

But the past few years have brought new developments. Scientists have gotten better at isolating DNA from fossils. They have also learned that perfectly preserved samples aren't necessary to build up lost genomes. Meanwhile, Haussler, benefiting from clever algorithms and massive increases in computing power, has made it much easier for them to fill in the gaps. If one scientist has sequenced DNA fragments from a woolly ­mammoth bone, and if Haussler has a tool that can re-create other parts of its genome, the two together put us a lot closer to seeing that beast at the local zoo. [....]
ople busy for a long time." [...]

Biologists can give you lots of reasons why ur-mammals won't roam the earth again anytime soon. For starters, genomes are really long. A typical mammalian genome contains billions of base pairs. Geneticists have no idea, at present, how to construct DNA sequences of such length and insert them into cells.

There's another big issue: mistakes. Haussler estimates that he could determine the ur-mammal genome with 98 percent accuracy. But of course there's no way to double-check without the original DNA. Plus, 2 percent is a lot. A human genome that was 98 percent correct would still contain 120 million errors, any of which could cause horrific problems.

The genomes of some extinct animals will be much harder to reconstruct than others. The ur-mammal has lots of present-day descendants, which is why Haussler chose it as his initial target, but dinosaurs don't. Reconstructing the genome of a Tyrannosaurus rex would therefore require inspired guesswork based on the genomes of related species like birds and turtles, as well as DNA fragments recovered from fossils. (And suddenly we're back in Jurassic Park.)

Then there are the unanticipated problems that come about when you fool around with nature. "There could be unforeseen interactions between an extinct species we bring back to life and ourselves," says Christos Ouzounis, an expert in computational genomics at the European Bioinformatics Institute in Cambridge, England. And even if we could re-create, say, a bronto­saurus, it would be plunked down in a place where it didn't belong and where it would have no adults to teach it how to be a proper brontosaurus


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