Why do humans cry when they are sad?

Question

I'm curious as to why humans are the only species that I know of that cries when emotionally upset. I have read that "emotional tears" help relieve stress, but why is it that only humans utilise such a mechanism? Why hasn't it popped up in multiple species if it chemically reduces an individual's stress when utilised properly? Shouldn't it be beneficial enough to move to other species?

Some people seem to be slightly confused about my question, since it kind of changes meaning from the headline...

My question is not necessarily why humans cry; I'm already aware that it helps relieve stress by releasing certain chemicals.

My question is why no other species uses the same kind of emotional tears as humans do. If emotional tears are beneficial, why haven't they moved onto any other species?

Answer 1

There are three types of tears are generated by the human eye. Basal tears protect the eye and keep it moist. Reflex tears flush out the eye when it becomes irritated. And emotional tears flow in response to sadness, distress, or physical pain.

Studies have shown that emotional tears contain more manganese, an element that affects temperament, and more prolactin, a hormone that regulates milk production. Sobbing out manganese and prolactin is thought to relieve tension by balancing the body’s stress levels and eliminating build ups of the chemicals, making the crier feel better.

But this minor physiological benefit aside, the most likely reason we produce emotional tears is because it’s a means of communication. Before babies can speak, they can cry. The only way for infants to express frustration, pain, fear, or need is to cry. Adults may use crying to bond with other humans. Expressing sadness can prompt comfort and support from peers. Different languages can provide barriers to spoken communication, but emotions are universal. There are also culturally acceptable reasons for crying that bring people together, such as at funerals or weddings.

Though there is a significant debate over whether animals have emotions and can express them, some animals do appear to cry for emotional reasons. Elephants seem to grieve when a family member dies and will guard the body and travel long distances to view it. Elephant experts at the London Zoo once told Charles Darwin that the animals do indeed mourn. Chimpanzees also appear to cry, but some scientists still insist that the tears released by these animals are strictly for cleaning the eye.

Great question!

Answer 2

good question - but I think fundamentally features such as crying to reduce stress only pass "down" the inheritance tree. So if some ancestor of, say, humans and platypuses cried to relieve stress we could expect that most relatives between humans and platypus would also cry. It's (in my thought experiments) extremely unlikely that two species would "develop" the same adaptation outside of a common ancestor (imagine, for instance, humans developing a beak like a bird - what advantage would it offer humans (or the subset of humans that had beaks)). I'm not sure what the evolutionary advantage is to crying under stress - perhaps it invokes protection from other family or tribe members. Maybe it says "look, I need protection, come save me from the saber toothed tiger". Cavepeople who cried survived the saber toothed tiger attack, those who did not cry, but took it like a man, perished. Now I realize a direct physical threat is different from emotional stress but the idea might be the same. Those who grieved the loss of a child by crying - and thereby enlisting protection of others - didn't get attacked by the saber toothed tiger.

Answer 3

There are three kinds of tears, and chemically they're all a little different. We have about 20 tear glands that contribute certain chemicals to the mix. The first kind of tears constantly washes over your eyeballs to keep them clean and moist. The second type is what you get when you chop an onion, break your arm or get dirt in your eye or have your ears pierced.

The third type is emotional tears.
Psychologists believe crying might also be a social signal that encourages others to comfort us or protect us in some way. Of course, we've put all kinds of taboos on crying, so busting out in tears in the boss's office might not be a good idea these days, but that's just stereotyping of criers as weak or out of control.

Also http://scienceline.org/2006/10/23/ask-driscoll-tears/

Answer 4

There is one other documented non-human animal that cries tears in an emotional response. That is the elephant. I have also read somewhere that all of the cetaceans (aquatic mammals such as the dolphins and whales) also cry tears that are different when they are an emotional response. All I am giving you are exceptions to the perceived rule that animals don't cry. I can't give a reason. I know that animals, pets in particular, do in fact have emotions. I don't know why they don't cry tears, but they do let us know their emotional state.

Answer 5

bonobo chimps do indeed use the same method with dealing with a crisis situation that impacts them in such a high degree. so to say that humans are the only ones to do this i think may be in error. the chimps cry after losing family members....

i would think that in highly developed animals have evolved this to be able to express emotions with visable results. noisey expressions in the very long ago past would have only served to bring predators to prey. our culture and lifestyles of current times still supports this as an appropriate action that brings about responses from others close to us for comfort and sympathy.

stress relief and manipulation both play a large part in why we cry.

Answer 6

"Humans are the only animals positively known to cry emotional tears of sadness and joy, though the vocal cries, whines, and whimpers of young mammals are similarly used to solicit aid from mothers. People report feeling better after a cry, according to a study by University of Minnesota biochemist, William Frey. Frey discovered the neurotransmitters leucine-enkephalin (an endorphin or natural opiate-like substance for pain relief) and prolactin (released from the pituitary in response to emotional stress) in emotional tears; the substances were not found in tears shed in response to sliced onions. (N.B.: Tears may help the body alleviate stress and cleanse itself of toxins, as do other exocrine processes such as sweat, urine, and exhaled air.)"

Answer 7

It's Scientifically Proven that Crying is a stress reliever! So when your up set alot of times it builds tension in your body even your muscles tense up! When you cry I mean really let it out your body relaxes itself! Maybe the reason it hasnt showed up in animals is because they very seldom I would venture to say never get stressed! They dont have to worry about money or any of the aspects we call "life"

Answer 8

That is a very good question. I have seen tears coming from the eyes of some animals, although I do not know if they are sad. Now I am curious for the answer to your question also!

Answer 9

It is a sort of exaust for excess of emotional build up in ones heart. You cry if you are sad and even if you are very happy. Other species too cry it is just we fail to observe. Try your luck on stray animals you will find they too cry.

Answer 10

my opinion would be that think about it- animals don't think about things the same way we do, with emotion. animals only know pain, and the instinct to survive. humans have emotions, in contrast, take, for instance, a hamster only knows how to survive- so a hamster doesn't cry when stacey steals her boyfriend.