It's called neotony. Domesticated dogs rarely howl, and domesticated cats rarely roar. Both of them keep the urge to play much longer than their wild counterparts.

One interesting side-note is the idea that humans are also domesticated animals, and that we self-domesticated. A large part of what makes us human is that we maintain a degree of brain plasticity as we age and don't ever fully become adults. A fascinating piece of evidence for this is the way that baby chimps resemble baby humans, both in looks and behaviour.

http://www.gmilburn.ca/2009/03/30/chimpanzees-and-neoteny/