| It is the nature of intelligent life to destroy itself

I was reading about the Fermi Paradox tonight at work, and I think my favorite explanation for why we haven't found alien civilizations is in the title. Then at least I can sort of ignore the melting ice caps and general destruction of the Earth. It's in our DNA.

Why do you think we haven't discovered any aliens yet, or do you think we have? The zoo hypothesis is pretty rad too.