All organisms vary, and it's just folk knowledge. You just have to look around a room of people, and everybody knows that it's true. Darwin didn't know the mechanism of heredity, but you don't have to. You just need to know the fact of it.
Stephen Jay GouldTransitional forms are generally lacking at the species level, but they are abundant between larger groups.
Stephen Jay GouldThe equation of evolution with progress represents our strongest cultural impediment to a proper understanding of this greatest biological revolution in the history of human thought.
Stephen Jay GouldPeople are clever, but almost no one ever devises an optimal quip precisely at the needed moment. Therefore, virtually all great one-liners are later inventions - words that people wished they had spouted, but failed to manufacture at the truly opportune instant.
Stephen Jay GouldForelimbs of people, porpoises, bats and horses provide the classic example of homology in most textbooks. They look different, and do different things, but are built of the same bones. No engineer, starting from scratch each time, would have built such disparate structures from the same parts.
Stephen Jay Gould