And btw, I've never seen an animal go into a school and kill innocent children. Neither have I seen an animal engage in cruelty, knowing full well what they are doing.
Here's an article about baboons going to war:
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8400000/8400019.stm
"What's interesting about hamadryas baboons is the way they control their social structure through aggression. Just seeing some of the males disciplining their females - it really is quite nasty," she says.
If a human was to control a female like that, would it be cruelty? Sure, there are evolutionary reasons for them doing that but the same could be same for humans, it doesn't make it any less cruel.
Here's one about killer dolphins:
http://www.telegraph.co.uk/earth/earthnews/3323070/Killer-dolphins-baffle-marine-experts.html
Film taken of gangs of dolphins repeatedly ramming baby porpoises, tossing them in the air and pursuing them to the death has solved a long-term mystery of what causes the death of so many of these harmless mammals - but has left animal experts baffled as to the motive.