Human relationships have specific properties. They persist, through time and space. They are reciprocal. They may be ascribed (kinship, group membership) or attained (friendship). They may be displaced through time and space. They are cognition intensive, mediated largely through language, the expressiveness of face and voice, and coordinated activity.
The cognitive and social impacts of language have been extensively explored. Evolution of the human face as a communicative organ and recognition marker extends a primate trend to visual orientation, freeing of the upper lip, and snout reduction and is reflected in hairlessness (incomplete in men); high integration of muscle and skin; complexity of musculature, including muscle-muscle insertions; different central neuroregulation of voluntary versus involuntary emotional expressions; and dramatically expanded representation of the face on sensory and motor cortices. Identification, reading, and tracking of faces are supported by expanded cortical regions and specific cell subsets within them for visual and emotion processing. Individually distinctive faces also aid recognition and recall of individual-specific information (social positionality, past behaviors) to guide behavior toward, treatment by, and social interactions with others.
The importance of cognition in human social relationships is attested to by high information and processing overhead. Acquisition of social knowledge is at least as important for survival and reproduction as acquisition of productive knowledge, being crucial for successful relationships. Additionally, emotional intelligence is required to navigate relationships, and all individuals must learn how to read the emotional content of situations and behaviors, communicative and otherwise, and develop the ability to regulate their own emotions and emotional expression. In this regard, emotional-cognitive bases for deferred gratification are critical to the spatiotemporally displaced reciprocity patterns humans pursue. Experiments with chimpanzees suggest that symbolic representation of “goods,” allowing abstraction and distancing, is a prerequisite (Beran et al., 1999; Boysen and Berntson, 1995). Performances of social reciprocity (e.g., conversation) are crucial to form and maintain social relationships in the short term and long term, and require integrated use of memory, signal processing, social intelligence, empathy, emotion processing, and behavior production (language, expression, gesture).
The skills necessary for such performances require extensive learning through observation, practice, and neurobehavioral honing during development. Reading emotion in others involves a formidable array of capacities: sense of self, theory of mind, cross-modality sensory mapping, integration of self and other (empathy), and expressive reciprocity to moderate ambiguity. Childhood may be extended to allow development of these emotional-cognitive skills.