The Expression of the Emotions in Man and Animals in the field of comparative psychology and his impact on academic psychology was muted, partly because of the widespread influence of the behaviourist school during the twentieth century. The lavish style of biological illustration was followed in work on animal locomotion by photographer Eadweard Muybridge (1830–1904)(leading to cinematography), and by the Scottish naturalist James Bell Pettigrew (1832–1908); in the extensively (and controversially) illustrated works of the evolutionary biologist Ernst Haeckel; and – to a lesser extent – in D'Arcy Thompson's "On Growth and Form" (1917). Darwin's ideas were followed up in William James' "What Is An Emotion ?" (1884); and,
Emotion in animals as when rolling and rubbing. Therefore, purring can be generally considered as an indicator of "pleasure" in cats. Low pitched bleating in sheep has been associated with some positive-valence situations, as they are produced by males as an estrus female is approaching or by lactating mothers while licking and nursing their lambs. The argument that animals experience emotions is sometimes rejected due to a lack of evidence, and those who don't believe in the idea of animal intelligence, often argue that anthropomorphism plays a role in individuals' perspectives. Those who reject that animals have the capacity to experience emotion do