Okay, first in a possible series of thought experiments*. Humans fall prey to Captain Tripps (the SuperFlu for you East Coast gangstas) and is wiped out. This leaves room for another species to take over as the dominant critters on the planet. What challenges do they face? Raccoon are a favorite of mine for this. They have reasonable hands, they're clever, and they adapt easily to different environments. They're now a urban species and doing well in our shadow. Would they necessarily need bipedalism? They can carry limited items now and a boost in size would help that further. (I've seen speculation that we gained size/stature before our brain developed, leading to a chicken/egg debate. Thoughts? *Octopi are on the list, anyone can start that one, I'm not territorial. Bound to be some I haven't thought of.