Honestly, I think it's natural, but girls hit it a bit later than boys. Javi has been flat out refusing to do things I tell him for a few months now. He either totally ignores me or he'll do the "Nooooooooo" thing or he'll throw something or hit something. Now, it's not all the time, but like you say it's on his terms. He helps when he *wants* to help. When he doesn't want to, forget about it.

Kids!