Of these 7 recent species most behave friendly towards respectful humans as most humans behave respectful to them. However, individuals of each species can get intimidated or ferocious if irritated by another species' member, getting the impression to be threatened, even by misinterpretation or lousy mood. read more
The answer is the same for both: intelligence. The more a species is intelligent, the more is capable for both good and evil actions because they have a concept of what they do. read more
Although gorillas are far more powerful, I’d be much more cautious around a random chimpanzee. Chimps are enough stronger than we are (roughly five times as strong, pound per pound) that we have no chance against them. read more