Facial expression the social component of those like shame, pride, jealousy, envy, deference, etc.) and are recognized by people regardless of culture, language, or time. The belief in the evolutionary basis of these kinds of facial expressions can be traced back to Darwin's "The Expression of the Emotions in Man and Animals." Reviews of the universality hypothesis have been both supportive and critical. Work in 2013 by Nelson and Russell and Jack et al. has been especially critical. Ekman's work on facial expressions had its starting point in the work of psychologist Silvan Tomkins. Ekman showed that facial expressions of emotion are
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