Answer: Past research
Explanation:
Past research is the technique of researching that has been done in prior about any particular subject and information regarding study got spread through publishing.It can be done by any person previously regarding any hypothesis or idea to test it and concluding outcomes .It is also known as previous research.This subject of research can be further researched.
According to the question, past Heracles is the reason behind the research idea that developed in mind of Joan .She wanted to investigate about the instable results that came from theory of criminal behavior impacting physical attractiveness.