Well, I think the answer lies in Fermi's Paradox somewhere. Simply put, all things being equal, the entire galaxy should have been colonized several times over, given exponential expansion. There should be evidence of intelligent life *everywhere.* Yet we have detected absolutely nothing intelligent beyond the boundaries of this planet. Nor any sign of life at all, even. How can this be? It is simply not possible. You should be able to close your eyes and point to somewhere in the sky and find an artificial structure, evidence of large-scale warfare, etc. But there's nothing. Yet, given the number of stars and planets, it's just not possible that we're the only intelligent life ever in the galaxy. Something more fundamental is at work here.
Some good reading:
http://www-personal.engin.umich.edu/...say/essay.html
http://www.sciam.com/article.cfm?art...mber=1&catID=2
http://home.tiac.net/~cri/1998/alien.html
http://faughnan.com/setifail.html
http://www.transhumanism.ndtilda.co.uk/Fermi.htm
Nobody really knows what the heck is going on. I think the answer lies outside metaphysics, philosphy or religion. I don't know if we'll ever know. All I do know is that there is definitely a missing variable in the human equation.