I want to know the answer to the following question:
What conclusion did Darwin come to after realizing that some diverse species were able to create variations easily, while other species thought to be closely related had difficulty?
All the background I'm provided with is that "Sometimes what were widely considered to be separate species produced fertile hybrid offspring freely, and in other cases what were considered to be mere varieties of the same species could only be crossed with difficulty.". Is that enough to answer the question?
Answer: no