In this period of prolonged development, children have fully developed motoric skills but are still very much dependent on the protection, nurturance, and guidance of adults. Gračanin and colleagues propose that there is a link between visible tear production and the unique prolonged childhood of humans. In particular, being moved, a complex emotional response mostly absent in children, is typically associated with silent tear production, occasionally in combination with chills or goosebumps (see later). The production of visible tears appears to gain relevance with increasing age, while the vocal component seems to lose significance. Second, whereas in animals crying is limited to vocal forms of expression (i.e., distress vocalizations, separation calls), in humans the shedding of visible tears is an essential additional feature (beginning in infants at approximately 4-8 weeks of age). First, in the vast majority of animal species, this behavior is predominantly displayed during infancy, whereas among adult members it is only exceptionally observed (with dogs as a notable exception, among others). This coupling at least suggests that humans at some point in their evolution were confronted with unique challenges for which the shedding of tears proved to be advantageous.ĭespite the similarities, humans differ in their crying behavior in two aspects from other animal species that exhibit distress calls. Gračanin and colleagues postulate that the connection between tears and vocal crying might have developed when, in human newborns, the strong contractions of the orbicularis oculi muscle during the production of distress vocalizations stimulated the sensitive corneal sensory nerves that then trigger the release of tears by the lacrimal gland (which is comparable with the production of non-emotional tears during yawning). Įmotional crying in humans seems to have its evolutionary basis in these animal distress calls, which is evident in its solicitation of help-provisioning and nurturing behavior. The similarity of the acoustic structure of cries across most primates, together with some other specific features of crying, suggests either that this characteristic acoustic structure arose early in primate evolution and had changed very little, or that there has been a considerable degree of convergent evolution toward an acoustic structure that is highly adaptive in a variety of habitats and social settings. This reaction to separation is typically immediate (i.e., reflex-like), appears to require no previous learning, and it is relatively consistent across different mammal and bird species. Whereas producing emotional tears appears to be a uniquely human behavior, human infants share the production of distress calls with the young of most other mammals and birds, which are typically displayed when they are separated from their mothers.
Future research is needed to comprehensively characterize the neurobiology of this intriguing and complex human behavior.Įvolutionary origins of human emotional crying and the adaptive functions of tears as a social signal Further challenges in elucidating the neurobiology of crying involve the complexity of crying behavior, which includes vocalizations, tear production, the involvement of facial musculature, subjective emotional experience, emotion regulatory behaviors, and social behaviors.
Currently, most of the research on the neurobiology of crying in humans has focused on autonomic physiological processes underlying tearful crying, which may yield essential clues regarding the neural substrates of the production of crying behavior and its effects on the crier. Despite an accumulating understanding of the neurobiology of human emotional crying, the primary sources of information are currently from animal studies and observations in neurological patients suffering from pathological crying. To set the context for this review, we first provide a brief overview of the evolutionary background and functions of tearful crying. In this paper, we review the current state of the literature investigating the neurobiological aspects of this uniquely human behavior, including neuroanatomical, neurochemical, and psychophysiological findings. Despite the ubiquity of this human behavior, research is only just beginning to uncover the neurobiological underpinnings of human emotional crying. The production of emotional tears appears to be uniquely present in Homo Sapiens.
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