Let us suppose that over an extremely long period of time, the size of the available mice began to grow such that an individual cat by itself could not successfully hunt them. Let us further suppose that the cats were clever enough to realize that their survival depended on cooperating with the neighbor cat in order to bring down the larger mice and thus feed them both. The cat must resist and suppress its inner urge to kill the neighbor cat and steal its food, for in doing so it would lose its hunting partner and thus endanger its own existence. Survival of the cat in these strange new circumstances depends on its ability to put aside some of the urges that it quite naturally feels. Societies or tribes are built on the notion that the group will be more successful and provide a more secure living condition than any of the individuals could achieve by themselves, and thus it is that by forgoing individual needs and desires and working for the good of the tribe, the individual's needs will be better met than if they were to try to go it alone.
Ethics come into existence when individuals join together in a tribal unit.
Before that occurs, they would have no awareness of good or evil, only the desire to take care of themselves, stay alive, and, when the opportunity arose, procreate. Not unlike cats. One way of looking at and understanding the Tree of the Knowledge of Good and Evil is to see it as representative of that time when humans joined together, formed a social structure and ethics came into being. Whether or not eating the fruit of a growing tree brought about the awareness of the efficacy of social structures is a matter for each individual to determine according to how they choose to understand scripture. There is another aspect of the creation of ethics and good and evil brought on by the formation of a society, and that is that instead of integrating the primal, and sometimes violent instincts with the new social and ethical structure, the individuals end up trying to suppress the instinctual aspects of the psyche that are incompatible with the social order.