Evolution, shmevolution. No matter how big your brains might get, the cuter animals will survive, because they are cuter and they will enslave you to be their stepping stone and the jumping board and a new starting point and the really serious new big deal. Yeah?, you think you are smart? Guess what, this is exactly what will make cute little overweight dogs survive...
Well, maybe not exactly that... but being the fittest sometimes means cutest. Yippiee.