The theory of evolution is supported by the theory of genetics, which provides a single causal mechanism to explain the activities of replicators and interactors. A common misrepresentation of the theory of evolution, however, is that interaction (involving interactors), and transmission (involving replicators), are distinct causal processes. Sandra Mitchell (1987) is misled by this. I discuss why only a single causal mechanism is working in evolution and why it is sufficient. Further, I argue that Mitchell's mistaken view of the causal mechanism in evolution prevents her from resolving the conflict between Dawkins and Brandon. I conclude that the unit-of-selection question remains very much alive.