Until recently, the arrow of natural selection seemed to go only one way. A species could form, then it could flourish, then it could go extinct. And once it was extinct, it could not come back.

Now, though, some scientists say they see a new path.

“Maybe we can no longer delay death, but we can reverse it,” said George Church, a Harvard Medical School geneticist.

For now, only one extinct subspecies has been brought back, and the baby animal that was born lived just minutes in 2003. It was a Pyrenean ibex, a large goatlike creature that lived in the Pyrenees between Spain and France until the last one died in 1999. The method used was cloning — using frozen cells of the last of the animals to try to create a new one, much like Dolly the sheep was cloned from a frozen udder cell of a sheep that had died years before.

Dr. Church said there could be some unexpected advantages to bringing back certain species, or even to adding their DNA to that of today’s species.

However I didn’t agree that.  The species deaths are natural selection decided or maybe most is man made.  But there biologic chains are no longer existed.  If we bring these species to the earth again, they will disturb the existing bio-chains.  We could not imaging the result of that.  In fact, our human really kill the species. This is not means we have to bring them back.  Before create them back, why not protect them before they extinct.

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