Firstly, why are animals used as adjective to describe the worst ways that humans can behave? It’s like how Indians, when the situation in our country is tanking, start comparing it to banana republics (of Central America). Hello, look at where we are. 

As far as I know, other animals are predators for food alone, and usually shun gluttony once hunger is satiated. They also rarely attack their own species. On both counts, human behaviour seems more ferocious, morally inferior.