Final answer:
None of the individuals listed (Freud, Watson, Skinner, Zimbardo) is widely credited with the simplistic statement that "man is an animal." However, Claude Lévi-Strauss discussed how humans define themselves against nature, which includes animals, and Frans de Waal has argued for the animalistic roots of human morality.
Step-by-step explanation:
The question "Who stated that man is an animal?" can be approached by considering various scholars' views on human nature. Although the common reference to this concept doesn't come from the provided options (Freud, Watson, Skinner, Zimbardo), it is worth mentioning that French anthropologist Claude Lévi-Strauss articulated that cultures define themselves against animals and nature. This idea corresponds with views that consider humans as part of the animal kingdom, but none of the specific individuals listed has been widely credited with stating that "man is an animal" in the simplistic terms of the question. Instead, each had their own theories regarding human behavior and psychology. For example, Freud focused on psychoanalysis, Watson on behaviorism, Skinner on operant conditioning, and Zimbardo on social psychology. Other thinkers, like Frans de Waal, argue more directly about the animalistic aspects of humans, in the context of morality and empathy being rooted in our primate lineage.