A larger head makes death during childbirth easier, so I'd expect evolution to be optimizing processing power per unit volume even today.
Unfortunately, neurons are about as efficient in most species - they're already as optimized as you get. For that and other interesting facts, see http://www.pnas.org/content/early/2012/06/19/1201895109.abstract
I was very interested in the discussions and opinions that grew out of the last time this was played, but find digging through 800+ comments for a new game to start on the same thread annoying. I also don't want this game ruined by a potential sock puppet (whom ever it may be). So here's a non-sockpuppetiered Irrationality Game, if there's still interest. If there isn't, downvote to oblivion!
The original rules:
Enjoy!