Why do we cry?
Here’s one theory:
Emotional tears have been shown to enhance the interpretation of sadness that is inferred from facial expressions. The current paper puts emotional tears in an evolutionary context. By using biological signaling theory, it first looks at the distinction between cues and signals, both of which provide information to recipients, except that signals have evolved for that purpose. The conclusion is that a signaling function has yet to be shown. Nevertheless, as emotional tears are likely to function as signals, an analysis of certain inevitable effects of tears on the individual hint at more than a single signaling function, depending on the context in which tears are produced. Emotional tears decrease the perception of gaze direction or of changes in pupil size, and may function as attenuators of intentions. Emotional tears are more likely, however, to function as handicaps. By blurring vision, they handicap aggressive or defensive actions, and may function as reliable signals of appeasement, need or attachment.
Source: Emotional Tears as Biological Signals from Evolutionary Psychology, 2009. 7(3): 363-370
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