Neurobiology of emotions in animal relationships: Facial expressions and their biological functions in mammals

This article aims to analyze the biological and communicative function of facial expressions and their relation to emotions in mammals. Facial expressions and their causes constitute an important yet largely unexplored field of scientific research. While the clinical usefulness of these expressions for recognizing pain in many species has been demonstrated, there is evidence that animals can also emit facial movements with other connotations. Reports show that facial expressions have a biological function by predicting and promoting social interaction in species that form complex social groups, but their meaning depends on the social context. For animals, the unconscious identification of facial expressions also implies an emotional value by modifying the compensatory physiological response, as occurs in species that have close relationships with humans. This corpus of evidence suggests that facial expressions have a kind of communicative function and may transmit emotions and, therefore, participate in affiliative or adverse relations as animals develop. Hence, exploring whether this nonverbal behavior may perform such a dual function is necessary.