Hey, Mr. Wizard, why do we cry?
Well, C-Dawg, the tears produced by our lacrimal glands rinse away the microscopic dust accumulated on our eyeballs, assisted by the wiping action of our eyelids when we blink.

Trust a scientist not to get it.

As babies, we cried. Sure, we cried when we were hungry, or ensconced in a soiled diaper, but that was just because we didn't know the words. We really cried when Mommy left us alone. We'd learned that something about our crying brought her running back every time.

But our power over her eventually faded away.

Later our crying became mostly related to physical injury. The first time we touched the hot stove -- they could probably hear our bawling two towns over. We ran home crying the first time the school bully beat us up. But Dad probably put a stop to that.

But eventually, rather than crying when we hit our thumb with a hammer or drinking a too-hot beverage, most of us took to swearing instead. I've often wondered why curse words are so much more effective here than other words. I, and I would guess many others, have tried on occasion to reprogram my reflexes to a more polite ejaculation, but the order to utter a "Golly" when I stub my toe just didn't take.

Now, as adults, our crying seems to be triggered by strong emotion. We cry when Mom or Dad dies. We cry when that special someone ignores us. But it's not just the sad things that can turn on the waterworks. We might cry at a sentimental word from that same someone. And, of course, Moms are famous for crying at their child's wedding. It can even be something we know in our minds to be unreal, but the heart has to have its way. They don't call 'em tear jerkers for nothing. We've all got at least one.

Sometimes, of course, the men in the lab coats can still give a reason. I'm sure there have been learned scientific papers written detailing the precise mechanism and evolutionary reason that we cry when we cut onions.

But mostly we don't know why we cry into our pillows, why we scream at the person who's not there.

I just know it helps.

Another aspect of the question is "why we cry" as responses to emotional or physical stimuli that have nothing to do with eye injury or contamination.

Drawing from cultural anthropology and evolutionary psychology one might conclude that crying is a method of communication that had to exist for preverbal cultures and modern human beings when in a preverbal phase of development.

If a member of a tribe was suffering in some way that could be addressed by another member of the clan, prior to the development of language, it would be to the overall evolutionary advantage of this genetic branch to have a mechanism by which this could be communicated.

Similarly, a baby who cries communicates (quite effectively, to the point of being a kind of low-tech auditory spam) his biological needs of feeding, changing, and the like.

Crying is also useful as a kind of intrinsic language that is generally difficult to fake. It is generally difficult for someone to ignore another person who is crying, probably due both to an evolutionary trigger of empathy, and also a more cognitive understanding that the person is likely not making a false or dissembling presentation of how he/she feels.

An interesting unanswered question is why evolution might have selected this specific physiological response, rather than another, such as, say, twitching elbows to indicate distress or strong emotion. Perhaps we are biologically geared toward looking at others' faces to gauge their "state", as a general heuristic.

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