animals. In Mental Evolution in Animals, Romanes illustrated the evolution of the cognitive and physical functions associated with animal life. Romanes believed that animal intelligence evolves through behavioural conditioning, or positive reinforcement. Romanes then published Mental Evolution in Man, which focused on the evolution of human cognitive and physical functions.

In 1890, Romanes published Darwin, and After Darwin, where he attempted to explain the relationship between science and religion. All of his notes on this subject