Herpetologist: Some psychologists attribute complex reasoning to reptiles, claiming that simple stimulus-response explanations of some reptiles' behaviors, such as food gathering, cannot account for the complexity of such behavior. But since experiments show that reptiles are incapable of making major alterations in their behavior, for example, when faced with significant changes in their environment, these animals must be incapable of complex reasoning. Which one of the following is an assumption required by the herpetologist's argument? ['Reptile behavior appears more complex in the field than laboratory experiments reveal it to be.', 'If reptiles were capable of complex reasoning, they would sometimes be able to make major changes in their behavior.', 'Simple stimulus-response explanations can in principle account for all reptile behaviors.', 'Animals could make major changes in their behavior only if they were capable of complex reasoning.']