Each year, an estimated 10,000 to 100,000 animal species die off. They join the countless species that have gone extinct over the course of Earth's history—and extinction means forever.
At least it used to. Scientists are now closing in on the ability to bring back extinct species. No, this doesn't mean the plot of Jurassic Park is going to become a reality. Researchers need DNA to bring back a species. DNA is the chemical that carries the structure for a living thing. Dinosaurs have been gone too long for any of their DNA to remain in fossils.
But there's a very real chance that we will be able to bring back more recently extinguished species. This could even include Ice Age animals like the woolly mammoth. In 2003, a team of Spanish and French scientists re-created the Pyrenean ibex, which had gone extinct three years earlier. The new animal didn't survive long, but scientific advances should improve the success rate. In January, Australian scientists announced that they were on their way to bringing back the gastric brooding frog.
Just because we can bring species back doesn't mean that we should. There may be benefits to reviving a species. But there's no way to know how it will turn out. For example, would a passenger pigeon fit into its old habitat? Or might it crowd out existing species?
Environmentalists worry that our ability to bring species back might cut down support for the hard work of traditional conservation. Why worry about preserving a wildlife habitat or fighting poachers if we know we can just reverse our mistakes?
But those extinctions are our mistakes to correct, which may give us an obligation to do so. As businessman and environmentalist Stewart Brand recently said, "Humans have made a huge hole in nature. We have the ability now ... to repair some of that damage."
We would do well to remember the lesson of Jurassic Park: Proceed with caution. And maybe leave the velociraptors be.
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"They're Back!" originally appeared in the May 3, 2013 issue of TIME FOR KIDS: Edition 5-6.