Saturday Night Live had a brilliant sketch back in the 70's or 80's that perfectly illustrated why the large-brained tend to go extinct. The sketch had a small band of caveman hunters gathered around the campfire at night after the hunt. Brutus, the leader of the band was a muscular and stupid jock who kept walking through the fire and burning his feet while boasting of his hunting prowess. One of the others, a proto-nerd played by Bill Murray, decided it would be a good time to bring up an idea he had about how they could catch more game if, rather than just chase after their prey, they could surround it and close in on it from all directions, making it harder for it to escape. The other cave men seemed to begin to grasp the concept until Brutus walked around behind the Murray character and dropped a boulder on his head. It remains my all-time favorite SNL sketch.