3. Smell signals

‘Smell signals’ looks at pheromones—chemical substances released by animals that cause a specific reaction in another of their species. The clearest examples of pheromonal communication come from insects, including bees, moths, and fruit flies. Scientists have found it harder to identify pheromones in vertebrates. There is chemical communication between animals, and examples of pheromonal signalling in mice, goats, and rabbits. For pheromone evolution to occur, both stimulus and receptor must change simultaneously. Pheromones are generally not proteins, so are not directly affected by genes. While humans are quick to accept the idea that they have pheromones, there is no decisive evidence.