It's interesting that very often the people who most stridently insist that humans are nothing more than animals are also the people who purposefully blind themselves to the lessons that nature teaches. Specifically, every type of mammal uses physical violence against their own kind to establish and maintain social and physical dominance. Not only is this behavior universal, but it's also essential to mammalian social structure. It's impossible for creatures to work together as a group without establishing a hierarchy, and physical force is the ultimate arbiter of authority.
Wolves are incapable of reasoning with each other, so the way they settle disputes is through (generally non-lethal) combat. The winner dominates the pack, and the loser submits or leaves. Similarly, adult humans cannot reason with children, because until the early to middle teenage years humans are incapable of concrete reasoning. It's pointless to try explain to a 5-year-old why he shouldn't throw the baseball in the house or how it hurts his sister's feelings when he refuses to share. He may appear to understand, but he doesn't. Words will make an impact for a few seconds, but the behavior will quickly return. One thing that will leave a lasting impression, however, is a good smack on the butt.
Physical punishment is important for children, but it should also be used sparingly and in love, not in anger. Spanking isn't a way for a parent to take out aggression or relieve frustration, it's a way to teach a child an important lesson that they may not be able to learn any other way. As with everything, balance is key. I've worked with children for a long time, and the worst ones are those who are never physically punished. They don't understand their place in the social order, they don't respect adults, and they don't obey because they never experience any negative consequences for disobedience. Our brains are wired to learn from pain for a reason.
He who spares the rod hates his son,
but he who loves him is careful to discipline him.
5 And you have forgotten that word of encouragement that addresses you as sons:
"My son, do not make light of the Lord's discipline,
and do not lose heart when he rebukes you,
6 because the Lord disciplines those he loves,
and he punishes everyone he accepts as a son."
7 Endure hardship as discipline; God is treating you as sons. For what son is not disciplined by his father? 8 If you are not disciplined (and everyone undergoes discipline), then you are illegitimate children and not true sons. 9 Moreover, we have all had human fathers who disciplined us and we respected them for it. How much more should we submit to the Father of our spirits and live! 10 Our fathers disciplined us for a little while as they thought best; but God disciplines us for our good, that we may share in his holiness. 11 No discipline seems pleasant at the time, but painful. Later on, however, it produces a harvest of righteousness and peace for those who have been trained by it.