Interesting topic.
I'd be more inclined to allow replacement of animals that have been hunted to extinction, or extinct due to man's actions, and not due to "natural selection".
Now, I know we can argue man causing extinction of animals is natural selection at it's finest, but tell that to the Auroch, the Tasmanian Tiger, the Great Auk, the Quagga, the Caspian/Persian tiger, and the Dodo- all hunted to extinction by man.
Oh wait- you can't.
The creation of genetic modified plant seeds is something I'm not too keen of. But it's happening.
I imagine the Woolly Mammoth will be resurrected too, whether we like it or not.