It's people (and animals) who are inclined to be vengeful or jealous.

Not too sure about animals showing these traits. Sure that may be our interpretation of their actions but this probably says more about us than it does about animals.

Is not the concept of illness (especially mental illness) and steps to deal with it, linked forever with religion? Is not 'ill' just another word for 'evil'? Is not disease thought by some to be the body pocessed by 'evil' spirits?