Yep. There's a reason why species go extinct. It's been happening for 100's of millions of years, and will continue on so long as the planet is habitable.
And, to those who say "Man caused (XXXX) to go extinct!!!!", remember that man is a species, too. It's no different than if the passenger pigeons were all eaten by saber-toothed tigers.
just my $0.02.
Bring back the saber-toothed tiger and t-rex.