As I recall you are right about this, John Thurston. Some apes kill in wars against each other, and some apes and some other creatures kill "adopted" young after taking on a new mate. I have heard evolutionary biologists claim that this is done so that a make can insure that his progeny get the food and attention of the parents, and that this way his genes will survive. This isn't an area I know much about, so I can't speak to this issue.
You made a good point, but despite these examples still I believe most animals (at least higher animals) are not predisposed to all-out combat to the death, and that the typical kill in nature is of an unusually weak prey by a clearly stronger natural predator (or pack of predators).
I suppose that we could look at the various "martial arts animals" and see which ones tend to kill young or kill in war, but I suspect that just compiling a list of martial animals could require a long thread.
As has been mentioned, domestic dogs generally have to be trained to fight, and of course cocks kill mainly because people put nasty blades (or barbs) on their legs.
It would be gruesome indeed to claim some link between martial arts animals killing their young and any sort of human martial arts practices.
I guess someone else might bring up the point that preying mantis (females I believe) kills and eats her prey after mating. Obviously these are "martial arts animals," but if a parallel can really be drawn between their practices and those of humans' martial arts, well, maybe I should stop encouraging my wife in her martial arts training