I want to know the answer to the following question:
What creatures did Darwin study that made him believe variation arose constantly?
All the background I'm provided with is that "He studied the developmental and anatomical differences between different breeds of many domestic animals, became actively involved in fancy pigeon breeding, and experimented (with the help of his son Francis) on ways that plant seeds and animals might disperse across oceans to colonise distant islands.". Is that enough to answer the question?
Answer: no