Imagine for a moment that our Earth is a quarantined world, a world unlike any other in the cosmos, and one with which contact is absolutely forbidden. If extraterrestrials found themselves stranded here, what would they do? Some might choose to live among us, and embrace our world as their adopted home. Others might distance themselves from human society and choose to live in seclusion, not in deference to some higher principle, but simply because they can't stand us.