Chapter VII (of the first edition) addresses the evolution of instincts. His examples included two he had investigated experimentally: slave-making ants and the construction of hexagonal cells by honey bees. Darwin noted that some species of slave-making ants were more dependent on slaves than others, and he observed that many ant species will collect and store the pupae of other species as food. <answer>He thought it reasonable that species with an extreme dependency on slave workers had evolved in incremental steps.</answer> He suggested that bees that make hexagonal cells evolved in steps from bees that made round cells, under pressure from natural selection to economise wax. Darwin concluded:
How does Darwin theorize that instincts have evolved in slave-making ants?
He thought it reasonable that species with an extreme dependency on slave workers had evolved in incremental steps.