Ellen: "I wonder though if this is something that is peculiar to humans only or if other creatures, given our level of intelligence, would exhibit the same behavior. Perhaps it's the price of higher brain function. Being at the top of the food chain, we must function as our own predator".
This is a worthwhile question, but let's preface it with her previous observation so that it is within context.
Ellen (responding to my point 2): "And although animals in nature kill, they kill for food. They kill to protect their young and to protect their territory (an exception, wolves and chimpanzees do engage in territorial skirmishes in packs) but they do not devise instruments of torture, they do not burn their own kind at the stake, they do not hang/draw and quarter/post the body parts on stakes, they don't turn their intelligence to weapons of mass destruction, they don't drag a man behind their truck for sport til he is barely recognizable as a man. (And according to certain scholars the commandant was not 'thou shall not kill' but rather 'thou shall not murder')."
In other words, to summarize (and I'm pretty sure I've got the point): "Do other animals kill for pleasure? Do they torture?"
To this I would say, "Yes" and "yes".
Any observant pet owner can guess that cats and dogs clearly enjoy killing things. I would hazard a guess that any predator of sufficiently complex brain organization also enjoys killing things. Is this murder? Well, if we go with my definition, killing purely for the joy of it, then yes.
It has been documented, for example, that many dolphins kill, rape, bully, and harass not only members of their own species, but other cetaceans and aquatic mammals. Killer whales (not really whales, but the biggest members of the dolphin clan), will "play with their food" - often tormenting, savaging, and tossing seals and other prey between themselves in games of catch.
Cetaceans experts, when asked about these behaviors, will rather hesitantly surmise that "they could be doing it for fun".
Now, there is good reason for them to be hesitant. The obvious caution is what is called anthropocentrism: ascribing human attitudes and attributes to non-human animals. Ethologists, scientists who study animals, often try to derive what animal minds are doing from overt behavior, and try to avoid assigning intentions to them. Attitudes are changing, however. As we learn more and more about brain structures, the commonality of brain function and behavior, it is slowly becoming popular to think that animals do indeed experience the same emotions we do. They feel joy, pain, pleasure, fear, suffering.
But, reverse that to the true notion, we have inherited all of our brain structures from life that came before us. We experience the same things animals do. We do so because we are animals.
Now, whether animals experience the joy of the kill as we do, may still be speculation, but I consider it a safe bet. From there, I would suggest that the observed overt behavior of joy of the kill is in fact a real internal mental state in animals.
However, I suspect there are two necessary conditions. The first is that of sufficient brain complexity. The animal must be sufficiently smart to be able to cogitate that the act plus the feeling equals the experience that can be repeated. In other words, it has to be smart enough to realize it can reward itself (in this admittedly gruesome way).
And the second condition ( and I think the more important) is that the animal must be social enough. Social animals while not strictly speaking in possession of a culture, nevertheless can pick up behaviors from each other.
Violence, at least for creatures on Earth, is an escalating hierarchy. Display threats come first, then the application of pain with minimal injury, then actually injury, then mutilation and maiming, then death. If a confrontation can be resolved at a lower level, it rarely ever moves to the next. Some biologists explain this as the result of microbes - the increased risk of infection and death has resulted in this hierarchy. I don't know if this is true, but the levels of confrontation in Nature certainly exist.
(This hierarchy of violence also seems to work not just at the individual level, but at the group level as well. Case in point. When the Roman Empire split in two back during Constantine's reign, you saw two fundamentally distinct strategies evolve. The western half (what we think of as the Roman half) continued its policy of war by attrition. The Eastern half (called the Byzantine Empire, but really the Roman Empire during the Middle Ages) followed a more flexible policy of appeasement/alliances/containment/conquest. The western half, pursuing the extreme, soon ran out of resources, and fell to barbarians. The eastern half, whose fortunes waxed and waned, lasted well into the 13th century. You tell me which strategy is better).
These are my, admittedly completely speculative and wholly undocumented, thoughts on the matter. I leave you with this, though. We must ask the question of when the quality of mercy enter into behavior? A certain empathy exists in most creatures. The question is, is this another form of the confrontation hierarchy, or is a certain complexity of behavior and socialization required?