Well, I think this episode confirmed my time travel theory.
We saw a short video on the DVD of the show that had a rabbit suddenly appear in duplicate and a scientist freaking out that they two identical rabbits couldn't come in contact with each other.
Now we have a Dharma polar bear in a archaeological dig.
We've had countless people who are supposed to be dead, show up alive, and fairly suddenly.
It think at this point it's safe to conclude that someone, likely Dharma, has a time travel device or other means of traveling through time.