A while back I wrote about neoteny in humans, and why most of us can't look at a bucket full of puppies without going "Aww!" It's all rooted in the evolution of the human brain, shaped by the millions of years something resembling Homo has been around. Jerry Coyne, author of the wonderful book "Why Evolution is True" (and author of a blog by the same name) gave his own take on the issue, which you can find here. I strongly recommend you give it a read! In it, he has a wonderful picture showing the neotenic evolution of Mickey Mouse. How could I not reproduce it here?