Tears for more than fears
Humans’ emotional tears are unique. How they developed is unclear, but they seem to be beneficial. So go ahead, have a good cry.
The main reason we cry, say evolutionary biologists and neuroscientists, is because we're human. (Gene J. Puskar / AP)
At mushy Hallmark commercials in which the son finally gets home on Christmas Eve. At weddings because everybody's so happy. At funerals because everybody's so sad. Even watching the Olympics, when I bond with the skaters who get teary because they've finally won.
But why, really, do I — do any of us — cry?
The main reason, say evolutionary biologists and neuroscientists, is because we're human.
As far as scientists can tell, no other creature cries emotional tears the way we humans do, despite scattered reports of an elephant or gorilla not just vocalizing in distress but actually shedding tears. (Intrigued by one such report of an Indian elephant crying after being captured, Charles Darwin sent a colleague to check it out; he couldn't confirm it.)
If emotional tears are indeed a uniquely human phenomenon, there must be an evolutionary advantage to crying, possibly a big one. But what? Does crying signal submission and thus disarm aggressors? Does it increase empathy and bonding, thus promoting community? Do tears promote health by relieving stress, thereby giving a survival advantage to the weepy? What is it about the human brain that creates this unusual ability to cry?
The lack of research money for such questions is enough to make a grown science writer cry. But some researchers are plunging in anyway, with fascinating results.
Behind the waterworks
Last year, for instance, psychologist Robert R. Provine at the University of Maryland Baltimore County reported in the journal Evolutionary Psychology that tears may have evolved to "enhance the valence," or give more oomph to, facial expressions of emotions, including sadness.
In an intriguing experiment, Provine's team asked 80 undergraduates to rate the intensity of facial expressions of sadness. Half of the images showed a person with tears streaming down the face, while the other half were the same images but with the tears digitally removed. These images were interspersed with "distractor" pictures of people with other facial expressions.
Regardless of age or gender, the students overwhelmingly ranked the pictures showing tears as conveying more sadness than the same faces without tears. More surprising, in the images without tears, students often perceived the faces not just as less sad but as expressing awe, concern, contemplation or puzzlement. In other words, says Provine, tears reduce ambiguity.
The fact that animals don't cry emotional tears — plus the fact that it takes newborns several months to add tears to their crying — buttresses researchers' belief that emotional crying is a recent evolutionary development, says Provine.
In a paper published in Evolutionary Psychology in response to Provine's work, Israeli evolutionary biologist Oren Hasson at Tel Aviv University theorized that emotional tears may also function as signals of appeasement. Because tears blur the vision of the person crying, they may be a biological signal of non-aggressive intentions, he said in an e-mail interview. They also act as a call for help and for bonding, conveying the message, "I can lower my defenses or attacking options, therefore you can trust me."
But there's another reason why emotional tears may have evolved, says William H. Frey, a biochemist, neuroscientist and author of the 1985 book "Crying: The Mystery of Tears." "I propose that humans evolved the ability to shed tears as a means to alleviate stress, and evolution favors this because it has survival value," says Frey, director of the Alzheimer's Research Center at Regions Hospital in St. Paul, Minn.
Viewing tears not just as communication signals but also as stress relievers may help explain why people don't just cry when there's an audience but also cry alone, when there's nobody around to receive the communication.
Evolution of tears
Emotional tears are chemically different from tears that simply lubricate the eye, Frey says: Among other things, they contain more protein.
The still-unanswered question, though, is whether there are more stress hormones such as prolactin and ACTH (adrenocorticotropic hormone) in emotional as opposed to lubricating tears, as one might expect if tears serve a stress-reducing function. So far, there have been no controlled, clinical studies to see whether emotional tears indeed reduce stress.
But there is a hint that crying emotional tears may improve immune function. A small Japanese study looked at 60 patients with latex allergies and measured their skin responses to latex before and after viewing two types of videos — one a neutral video about weather, the other, "Kramer vs. Kramer," what some viewers might find to be a tear-jerker. Nobody cried at the weather video, but most patients cried at "Kramer vs. Kramer," and in the weepy patients, skin reactions to latex were reduced.
Moreover, 85% of women and 73% of men say they "feel better after crying," which supports the stress-reduction hypothesis, says Frey, adding that, on average, women cry more than men — 5.3 times a month versus 1.7 times.
Precisely why women cry more is not known, but researchers do know that male and female tear glands are anatomically different. Female lacrimal glands, which produce tears, have smaller cells, says Darlene Dartt, a senior scientist at the Schepens Eye Research Institute in Boston. Hormones may play a role too, she says.
Researchers are also trying to puzzle out exactly what thoughts or feelings in which parts of the brain cause the lacrimal glands to secrete tears.
To unravel this, Dr. Josef Parvizi, a neurologist at Stanford University, studies patients who have abnormally frequent and intense crying and laughing spells, that is, "pathological laughing and crying," a condition that often occurs after multiple sclerosis, strokes, tumors, epilepsy or traumatic brain injury. These patients typically do not laugh or cry because of a mood disorder such as depression, but laugh and cry excessively and inappropriately because of brain damage.
Emotional tears are probably triggered, says Parvizi, by nerves running from the limbic system, the part of the brain that controls emotion, to the brainstem (at the top of the spinal cord) and from there to the lacrimal glands, which produce tears. It makes sense, says Parvizi, that many brain systems are involved because both laughing and crying involve understanding the emotional context before inducing appropriate changes in the musculature of the face, the larynx (getting choked up), the eyes, the heart rate and respiration.
At the very least, this elaborate brain system suggests that emotional tears are important. As Provine of Maryland puts it, "This is evolution occurring right before us. We're getting a ringside seat about exciting things happening."
Read other articles by Judy Foreman at myhealthsense.com.