Final answer:
The introductory section best explains why some have trouble believing in evolution; it suggests controversy within both public and scientific communities contributes to skepticism.
Step-by-step explanation:
The section from the article that best explains why some people have a hard time believing that evolution is real is the Introduction, where it is mentioned that perspectives and opinions on human origins and biological variation are highly debated, not only within the mindset of the general public but also amongst scientists. This suggests that the controversy itself, perhaps due to a combination of scientific discourse and public misunderstanding, makes it difficult for some people to accept evolution as a fact. The sections on Anatomical Evidence For Evolution, Fossil Record, and Homologous Structures provide proof of evolution but do not directly address why people might have difficulty believing in it.