Tears of sadness, joy, salt, and manganese
 

Emotional tears are believed by many researchers to be likely to be unique to humans, and unlike vocal crying they develop months after birth. Perhaps surprisingly there remains some controversy over their true relationship to human emotional expression.

Robert Provine at the University of Maryland experimentally demonstrated how tears can help us interpret the sadness of an otherwise ambiguous face. Provine digitally removed tears from photos, and the faces became very difficult to interpret emotionally. The people in the photos were rated less sad, and their faces were often mistakenly interpreted as expressions of awe, puzzlement or concern.

So tears may play a fundamental signalling role in human behavior, and not just be a correlate of emotional expression and a way to dispose of manganese. This experiment itself is suggestive although it leaves a lot of room for interpretation.

Interesting that this seems to be trivially obvious to most people. I think many evolutionary psychology theories sound intuitively right, which is part of why we tend to be suspicious of them! On the other hand, there are folks who seem very convinced that tears are purely a mechanical process that happens to accompany some emotional expression as an artifact, so I think it is worth exploring further.

PDF --> http://www.epjournal.net/filestore/EP075256.pdf

John Tierney (NYT) commentary --> http://tierneylab.blogs.nytimes.com/...ned-to-cry/?em