Complex Tears: Why Humans Like to Cry: Tragedy, Evolution, and the Brain
by Michael Trimble
Oxford University Press, 2012 ($29.95)

Mammals can all produce tears, yet humans are the only ones who cry. In his new book Why Humans Like to Cry, neurologist Trimble delves into how evolution and culture seemingly shaped the human brain to express emotion on a higher level than the rest of the animal kingdom.

Weeping may have been one of the earliest forms of hominid communication. Initially a method to keep the eye lubricated and a response to pain, Trimble argues that crying became a way for early humans to share feelings of sorrow, joy and compassion and to empathize with others long before we developed language.

Human emotions arise from a network of interconnected brain regions. Trimble discusses research findings that show our brain's emotionally driven limbic system is deeply connected with other areas of the nervous system, such as the sensory cortex, which helps us process our surroundings. As a result, our feelings are integrated with our environment and bodily responses, a different paradigm than occurs in other species. In fact, he suggests that one possible reason we feel better after crying is that weeping stimulates our cranial nerves, which in turn appears to soothe our overactive amygdala.

Trimble also describes how various art forms, especially music, carry the power to elicit tears. This phenomenon can be explained, in part, by brain-imaging studies that show music can tap into the limbic system of the brain. Simple chords can evoke memories, physical reactions, and feelings of joy and sadness. In one study, researchers found that of 83 people listening to poignant music, 90 percent experienced shivers and 85 percent shed tears. Another study showed that familiar songs triggered emotional memories in listeners.

Trimble ambitiously cracks the surface of a complex human process. Crying, then, does not indicate weakness; rather it highlights our advancement.