Quote Originally Posted by Dr. Egon Spengler View Post
I agree with you there. Life can exist without the exact same circumstances as on earth, such as plants developing to turn CO2 into oxygen. But plants aren't intelligent, are they?
They very well could be. I do believe the International Laboratory of Plant Neurobiology (LINV) located at the University of Florence has been researching plant intellect and they may be capable of some rather interesting feats.

Smarty Plants: Inside the World's Only Plant-Intelligence Lab
It's an article from 2007, but talks about what I was suggesting earlier. Perhaps a lifeform (like one on another planet) mightn't need a human brain to be considered 'intelligent'. They may and likely would develop something that works differently that still provides a high level of intellect which might even surpass our own in some cases. But as we've never come across such beings yet, we just don't know. And we ourselves personally may never know, as it doesn't seem all that likely to me that we'll ever make contact with them. Some might develop the means to come looking for us at some point in time though.