Final answer:
Helen Fisher emphasizes that the role of testosterone in human sexuality is complex and not fully understood, highlighting the neurochemical influences beyond simple stereotypes.
Step-by-step explanation:
Physical anthropologist Helen Fisher notes that it's important to recognize that the role of testosterone in human sexuality is complex and not fully understood (option b). Testosterone is not only present in males but is found in all genders, contradicting option a, and it is not solely responsible for female sexual desire, contradicting option c. While it is true that testosterone levels may decrease with age, option d does not address Fisher's emphasis on the neurochemical's complexity in relation to human sexuality. Additionally, issues like hypogonadism and disorders such as Prader-Willi syndrome reveal the intricate relationship between hormones and sexual function.