Wolves often get caught into steel traps.
How do they escape?
Well, they wait until the captured limb goes numb and then just bite it off. This unvoluntary self-amputation happens not only to wolves, foxes, sables and over predators in the wild, but also to domestic dogs and cats, trapped in urban hazards like moving rails at a railroad point and other machinery.
What does the escaped wolf do? He licks his wound until it cures and tries to return to his family. Wolves hunt in groups, by wearing down a chased prey. Their victims are often weak and injured species. By eating up all inferior species, wolves sanitize the species genes, ensuring only the best representatives pass on their genes. This is how evolution works.
And wolves, the sanitaries themselves, are no exclusion to that rule. Normally, family would reject the handicapped wolf and he has to hunt on his own. Of course, having only three legs renders him a poor hunter, and he is almost sure to perish. No matter was he stupid to get into that steel trap or just stupid, his genes are wiped out of the DNA fund of the species.
On the contrary, the highly social human society allows care for disabled individuals. The more developed the society is, the more unacceptable it is to abandon inferior species. Perhaps, the human is not that ultimate predator as some tend to believe.