You wouldn’t guess it from these photos, but it’s rare for animals to kill members of their own species—at least among mammals, in which less than one percent of deaths are caused by intraspecies violence.
That’s not to say that fighting is unusual. Far from it: competition over resources, struggling for dominance within the group, and conflict over mating often cause clashes, whether lethal or not. (Watch this "homewrecker" penguin defend his new abode.)
Some incidences only seem to be violent, as was the case with this bull elephant whose apparently aggressive behavior was likely playful.
And some—for instance, female bees who wage devastating, inexplicable wars—leave humans simply stumped.
So while it may not exactly be a dog-eat-dog world out there, rest assured: there’s plenty of fighting spirit to go around. (Watch: Kickboxing Kangaroos and 4 of Nature's Most Impressive Fighters)