One thing we take for granted is that once a species has been driven to extinction, that's it. It's gone. No more, ever again.
Do not take this as any sort of sign that it's suddenly okay to drive animals to extinction. But according to Stewart Brand in today's TED talk, given last month in Long Beach, California, the damage may, in the future, be reversible. Which is a huge opportunity... assuming nature hasn't readapted to go on without them. And assuming people in fact don't start taking it as a sign that extinction is suddenly okay to cause. But anyway, yay for science.