It's odd, isn't it, that we use this word to describe abuse and torture of prisoners. The reason it's odd is that I'm not sure any animals torture. Yes, they can kill and maim and inflict dreadful suffering in the process of killing, eating or fighting. But the act of intentionally exploiting suffering, of lingering over some other being's pain - using it as a means to an end - is not an animal instinct, unless I'm mistaken.
And so torture is in fact extremely human; it represents in many ways humankind's unique capacity for cruelty.