Why We Cry: The Science of Sobbing and Emotional Tearing
By Maria Popova
The human body is an extraordinary machine, and our behavior an incessant source of fascination. In Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond (public library), psychology and neuroscience professor Robert R. Provine undertakes an “analysis and celebration of undervalued, informative, and sometimes disreputable human behavior” by applying the lens of anthropologically-inspired, observational “Small Science” — “small because it does not require fancy equipment and a big budget, not because it’s trivial” — to a wealth of clinical research into the biology, physiology, and neuropsychology of our bodily behaviors.
Take, for instance, the science of what we call “crying,” a uniquely human capacity — a grab-bag term that consists of “vocal crying,” or sobbing, and “emotional tearing,” our quiet waterworks. Provine explains:
As an adult, you cry much less than when young, and your crying is more often subdued, teary weeping than the demonstrative, vocal sobbing of childhood. . . [T]he trauma that causes your crying is now more often emotional than physical. However, whether intentional or not, as adult or child, you cry to solicit assistance, whether physical aid or emotional solace. Paradoxically, your adult cry for help is more private than the noisy, promiscuous pronouncement of childhood, often occurring at home, where it finds a select audience. The developmental shift from vocal crying to visual tearing favors the face-to-face encounters of an intimate setting. The maturation of inhibitory control gives adults the ability to select where and when crying occurs, or to inhibit it altogether, options less available to children.
To better illustrate the physiology of crying, Provine contrasts it with that of laughing, pointing out that the two are complementary behaviors and understanding one helps understand the other.
Specialists may argue whether there is a typical cry or laugh, but enough is known about these vocalizations to provide vivid contrasts. A cry is a sustained, voiced utterance, usually of around one second or more (reports vary), the duration of an outward breath. Think of a baby’s ‘waaa.’ . . . Cries repeat at intervals of about one second, roughly the duration of one respiratory cycle . . . A laugh, in contrast, is a chopped (not sustained), usually voiced exhalation, as in ‘ha-ha-ha,’ in which each syllable (‘ha’) lasts about 1/15 second and repeats every 1/5 second.
One curious feature crying and laughing have in common, which any human being with a beating heart can attest to:
Crying and laughing both show strong perseveration, the tendency to maintain a behavior once it has started. These acts don’t have an on-off switch, a trait responsible for some quirks of human behavior. Whether baby or adult, it’s easier to prevent a bout of crying than to stop it once under way. Crying causes more crying. Likewise, laughter causes more laughter, a reason why headliners at comedy clubs want other performers to warm up the audience, and why you may be immobilized by a laughing fit that can’t be quelled by heroic attempts at self-control. In fact, voluntary control has little to do with starting or stopping most crying or laughing.
So, if vocal crying evolved to attract help, what’s the evolutionary purpose of quiet tears? For one, they contain lysozyme, the body’s own antiseptic, which sanitizes and lubricates the eye. But, Provine argues, there might be something much more interesting and neurobiologically profound at work:
Several lines of evidence suggest that the NGF [nerve growth factor] in tears has medicinal functions. The NGF concentration in tears, cornea, and lacrimal glands increases after corneal wounding, suggesting that NGF plays a part in healing. More directly, the topical application of NGF promotes the healing of corneal ulcers and may increase tear production in dry eye . . . Although more of a scientific long shot, I suggest that tears bearing NGF have an anti-depressive effect that may modulate as well as signal mood.
Non-emotional, healing tears may have originally signaled trauma to the eyes, eliciting caregiving by tribe members or inhibiting physical aggression by adversaries. This primal signal may have later evolved through ritualization to become a sign of emotional as well as physical distress. In this evolutionary scenario, the visual and possibly chemical signals of emotional tears may be secondary consequences of lacrimal secretions that originally evolved in the service of ocular maintenance and healing.
If anything, Provine points to this as a direction of curiosity for future research:
Emotional tearing is a uniquely human and relatively modern evolutionary innovation that may have left fresh biological tracks of its genesis. The contrast of the human lacrimal system with that of our tearless primate relatives may reveal a path to emotional tearfulness that involves NGF. NGF may be both a healing agent found in tears and a neurotrophin that plays a central role in shaping the neurologic circuitry essential for emotional tearing during development and evolution. A lesson of NGF research is that pursuit of the scientific trail can lead to serendipitous discoveries both broad and deep. Emotional tears may provide an exciting new chapter in the NGF saga, and vice versa.
The rest of Curious Behavior goes on to explore such seemingly mundane but, in fact, utterly fascinating phenomena as yawning, sneezing, coughing, tickling, nausea, and, yes, farting and belching.
Photograph via Flickr Commons
Published September 7, 2012