Crying is a waste of perfectly good water. So why we do it? I have no idea, so I would like to hear your ideas. To get the ball rolling, here are eight hypotheses, each surely inadequate and probably false.

(1) Purple Haze: When the tears “well up” under the skin, even before overflowing, the skin changes color, darkening and becoming purplish. Given that our color vision may have evolved for seeing skin color changes (do a Google search of “primate rump” but without the scare quotes to find my paper on this), one wonders whether tears are all about changing the skin’s color while still under the skin. Perhaps the flowing-over of the tears is just a side story. It seems, however, unlikely that the overflowing tears is just a side effect. Why not reabsorb it? And once the tears come out, it is likely the more visually salient feature, not the purple bags of skin under the eyes. 

(2) Seen Sheen: Perhaps the water visibly in the eyes and on the face creates a highly salient sheen, and this is the key. We are, indeed, highly sensitive to the signature “glimmer” of water, and perhaps this makes the face’s sad emotion easier to see. But modifying the face via muscle expressions would seem to be even easier to see. And even if tear-sheens are especially visible, why should sadness (and to a lesser extent happiness) be the emotion that utilizes this trick?

(3) Unstoppable: It can be very difficult to control a cry – which is why at the Harley Club Movie Night I go to the bathroom just before Bambi’s mother is shot by hunters – and that kind of uncontrollability is often a virtue for emotions. It let’s the viewer “know” he or she is not being manipulated. This could be part of the story of cries, but we would want to know why color signals (mediated via blood physiological changes under the skin, like blushes and blanches) aren’t enough, because color signals are also out of our control.

(4) Water-Handicap: On the topic of manipulating others, another way to convince others that you’re sad is to sacrifice something important to yourself. Perhaps tears are the sacrifice: by giving up perfectly good precious water, the crier is generally deemed to be more honestly signaling. …because crying is costly.

(5) Salt-Lick: Tears are salty and wet, just the thing animals love to lick. Perhaps tears are put out to attract grooming behaviors and intimacy from loved ones. (…who love you even though they need to be bought off by salt-licks to come to your aid.)

(6) That Wet Feeling: This idea is from my seven year old daughter. “Perhaps,” she said, “tears let us feel how sad we are.” The idea that our facial expressions are crucial in driving our inner emotions – rather than the other way around – has a long history. My daughter wasn’t intending to refer to that, I don’t think, but, rather, that the wet feeling on one’s face helps give one better feedback about how sad one appears to others. Rather than the usual proprioceptive sense of our facial expressions, her point was that the wet feel of tears is a special, extra proprioceptive sense of our sadness expression. The wet skin may even make the muscular facial expression easier to sense (i.e., in addition to the intrinsic wet feel). Why, though, should this extra-powerful proprioceptive sense be especially needed for sadness?

(7) Wet-for-a-While: Once the tears have overflowed, they stick around until they evaporate (or until the last lick of your, ahem, loved ones). To the extent that the tear-glimmer serves to signal sadness, one can keep up the sadness signal without having to put on one’s sad face. Relax your face, and let your water do the fussing on your face for the next ten minutes. 

(8) Bucket-O-Tears: Facial expressions due to muscles on the face don’t tell you how long they’ve been being expressed. Tears, on the other hand, are more “additive”. The more you cry, the wetter your face, and eventually your neck, chest and Bowling Enthusiast magazine. Why, though, would this kind of “additivity” matter for sadness and not other expressions?

With the quality of my thinking on this matter out on the table, hopefully you now feel no inhibition whatsoever to propose your own idea. And if we can put together a somewhat coherent one, then we can look into how we might test it.

But don’t be a cry-baby about it.