As part of a host of many emotional responses humans have, crying is pretty interesting (of the cathartic, grieving, or joy varieties… physical pain seems pretty obvious, but still interesting.)
Also, are there any other animals that’ve been shown to grieve?
Apparently elephants grieve.
Whales too.
Actually, I thought the OP was going to ask specifically why, when humans get emotional, does excess fluid come out of our tear ducts? What would be the evolutionary pressure to drive this behavior?
Totally SWAG, but social bonding - tears can show feeling for others, showing empathy.
Cite: Dune - where Paul cries for the Fremen he killed in the duel (water being extra precious there he got big points)
Cite: Ender’s Shadow - where the girl (can’t think of her name) cries for Poke and gains Bean’s support
Yeah, those are crappy cites, but the idea is there.
Because being able to give a subtle alert of distress to only those around you (therefore, presumably your allies/tribesmen) and not everyone you know, such as enemies, allows for transmission of information without giving away a weakness.
Definitely a huge part of it.
It seems like something that would’ve been naturally selected for as our minds became more capable of empathy, therefore outward physical emotion would become very important in attracting mates, especially during a time before true language was developed.
So does pissing your pants. Turning the argument around, having your eyes well up with tears and interfering with your vision when you need to be able to see to defend yourself seems contradictory.
Slightly off topic but related: I have noticed that a Japanese native
Along those lines, the spontaneous expression of pain is also culturally learned. As a native speaker of English, when I stub my toe I say “ouch” but for a Japanese the equivalent “eeeta” which sound similar to the Japanese term “itai” (pronounced " ee-ta-ee"). I don’t speak Spanish, but I have also noticed that my Latino friends who are native Speakers say “ah-yeee” when they hurt.
I recall reading that some research indicates the chemical composition of tears indicates they may have a function beyond just signaling distress to others. Just did a quick check, and here’s the cite, including the cites from the poster. Sorry it’s long, but it IS pretty interesting, I think:
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All tears contain 3 chemicals released by the body during stress. They are: 1) leucine-enkephalin – an endorphine believed to modulate pain sensation 2) ACTH – a hormone considered to be the body’s most reliable indicator of stress and 3) prolactin – the hormone which regulates milk production in mammals.
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Emotional tears contain more proteins than irritant'' tears, the kind you shed while slicing onions. Though Frey thinks this means that something unique happens when people cry emotional tears,‘’ other scientists have their doubts.
Both emotional and irritant tears contain 30 times more manganese than is found in blood, suggesting that human tear glands can concentrate and remove substances from the body.
http://www.boston.com/globe/search/stories/health/health_sense/102196.htm
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Scientists distinguish three kinds of tears, which differ from each other by function and also, probably, by composition. Basal tears actually form continuously. We don’t experience these minute secretions as tears because they don’t “ball up” as we are used to tears doing; instead, every time we blink, our eyelids spread the basal solution out over the surface of our eyeballs. Basal tears keep our eyes lubricated, important in preventing damage by air currents and bits of floating debris.
Basal tears, like all tears, have numerous components. A little bit of mucus allows them to adhere to the eye surface without causing harm. The main part of a tear contains, predictably, water and salts (like sodium chloride and potassium chloride). The ratio of salt to water in tears is typically similar to that of the rest of the body, so there is no net change in salt concentration; nonetheless, if the body’s salt concentration climbs too high, it will take advantage of the tear solution and instill it with extra salt. Tears also have antibodies that defend against pathogenic microbes, and enzymes which also contribute to destroying any bacteria the eye encounters. A thin layer of oil covers the tear’s outside to discourage it from falling out of the eye before its work has been done.
Our eyes produce irritant tears when hit by wind or sand (or insects or rocks). Irritant, or reflex, tears have the same constituents as basal tears, and work toward the same goal: protecting the eyes. However, since they are designed to break down and eliminate eyeball-intruders like airborne dust, these tears tend to flow in greater amounts and probably contain a greater concentration of antibodies and enzymes that target micro-organisms. Thus, irritant tears are not just basal tears in greater quantity; different biological processes precede the excretion of the two types of solution.
The voluminous tears that so rapidly move us to frustration or pity are, of course, emotional tears. Secreted in moments of intense feeling – sometimes joy, but more often sorrow – these tears aren’t there to cleanse the eyes of irritating microbes or debris. Yet they do serve a purpose; the function of emotional tears can be inferred from their constituents. Emotional tears contain much more (maybe 25% more) than basal or irritant tears of a certain important ingredient: proteins.
What do proteins do? Well, what can’t they do? We know very well they can be involved in anything and everything. The proteins found in emotional tears are hormones that build up to very high levels when the body withstands emotional stress.
If the chemicals associated with stress did not discharge at all, they would build up to toxic levels that could weaken the body’s immune system and other biological processes. But here, as in other areas, the body has its own mechanisms of coping. We secrete stress chemicals when we sweat and when we cry. Clearly, then, it is physically very healthy to cry, regardless of whether or not it feels awkward or embarrassing socially. The reason people will frequently report feeling better after a well-placed cry is doubtless connected to the discharge of stress-related proteins; some of the proteins excreted in tears are even associated with the experience of physical pain, rendering weeping a physiologically pain-reducing process. Conversely, the state of clinical depression – in which many of the body’s self-healing processes appear to “shut down,” including, often, emotional tears – is most likely exacerbated by the tearless victim’s inability to adequately discharge her pent-up stress. Psychologists refer to freely weeping as an important stage in the healing process. But although this notion may appear to be psychological in origin, involving the confrontation of one’s own grief, it also just applies physiologically: crying can reduce levels of stress hormones.
Good read, Romeo.
Maybe I need to start inducing myself to cry before bedtime. Stress keeps me up at night 
I simplified for brevity, but crying as distress signal is one of the things scientists actually do think helped lead to its evolution.
Wonder why this tear mechanism kicks in when you are laughing hysterically- wonder if laughter & crying are physiologically similar
You can’t leave us hanging after that, you know. How do people cry in Japanese culture?
Hard to describe - kind of a hiccuping sound with a bit of a whine at the end of each segment, starting at a higher pitch with a glissando to a slightly lower pitch at the end with a faint wavering, vibrato effect at the end of each cycle.
Ok so I cannot myself read the attempt at description above without finding it funny and hard to get. I’ll try to make one of my Japanese friends cry and do a sound recording for posting!
Infants need a way to communicate something’s wrong (in species where the parents raise their young). Many animals have such crying of their infants, and will resort to it when in distress as a adult.
Hard to describe - kind of a hiccuping sound with a bit of a whine at the end of each segment, starting at a higher pitch with a glissando to a slightly lower pitch at the end with a faint wavering, vibrato effect at the end of each cycle.
Ok so I cannot myself read the attempt at description above without finding it funny and hard to get. I’ll try to make one of my Japanese friends cry and do a sound recording for posting!
This sounds nice and all, but the body has plenty of ways to deal with proteins it doesn’t need anymore and homeostatic mechanisms to keep things going the right way. In particular, hormones often have short half lives because you want to have tight control over when you’re sending what signal. For example, ACTH has a half life of 10 minutes. Cortisol, another important stress hormone, has a half life around an hour, varying somewhat by individual. I’ve done some more looking, and I have yet to find any credible evidence - not speculation - that the incidental excretion of stress hormones in tears has anything influence on their rate of turnover. It seems just as plausible, if not more, that there are biochemical changes in the brain associated with crying that may temporarily affect stress hormone production. It is not surprising that hormone levels in various excretions, such as tears and saliva, are correlated with blood levels, but correlation does not equal causation.
True, but human babies don’t shed actual tears when very young, and other animal babies don’t do so at all. Certainly wailing alone is sufficient.