Final answer:
Juan's doctor attributes his strong, muscular build and aggressive tendencies to high levels of testosterone, a key male sex hormone responsible for male physical characteristics and linked to aggression in some studies.
Step-by-step explanation:
The male sex hormone that Juan's doctor attributes both his physical and behavioral characteristics to is testosterone. This hormone is crucial for the development of masculine characteristics. It promotes increased muscle mass, which explains Juan's strong, muscular build. Testosterone is also responsible for the secondary sexual characteristics in males, such as the deepening of the voice, growth of body hair, and an increase in sex drive that occur during adolescence. Additionally, the role of testosterone in aggression is complex, as some studies suggest a link between high levels of testosterone and aggressive behavior, but this relationship is not definitive due to varying study results, methodological issues, and the potential influence of environmental factors on behavior.