Shrinking of the brain in humans
3.2.2 Delayed development (Neoteny): Domesticated animals (and humans as self-domesticated apes) retain youthful traits for longer. A wolf puppy and a dog puppy look similar, but the dog stops growing its skull and jaws (and brain) sooner. Compared to Neanderthals or early Homo erectus, humans have a more 'puppy-like' skull: smaller, rounder, with a shorter snout. This is a direct result of selection for less aggression and more social tolerance.