The correct answer is the second option: "their behaviors are the result of the interaction of nature and nurture".
The nature vs. nurture debate is a popular debate in the social sciences when determining the causes of an individuals' behaviors, actions and personality. If someone's behavior or personality results from their 'nature', it means that their genetics and internal biological factors lead to their behavior. On the other hand, if someone's behavior or personality results from their 'nurture', this means that environmental and external factors such as socialization, family environment, living conditions, etc., lead to their behavior.