Anyone with experience of being human knows that feeling ‘sad’ is often a very complex thing. When we’re young children, our emotions tend to polarise into the two categories happy and sad; and part of growing up is gradually discovering the words which enable you to name and express exactly the many subtler feelings contained by these two broad, limiting words. ‘Sadness’ is a very general term. We can feel sad due to a mixture of many subtler emotions related to sadness, or even just from one of them: loneliness, disappointment, grief, worry just to name a few. But then, deceptively, we can also feel sad just because we simply feel…sad. (I said it was complex.) And for many – depending on your disposition – crying isn’t even exclusive to sadness: we cry when we’re in pain, stressed, angry, frustrated; some even do it when they’re feeling overwhelmed with happiness!
First of all, can you imagine what it must have been like the first time one of our human ancestors ever cried?
Picture it: you’re sat on a savannah somewhere in the heart of early Africa with a member of your group picking at some fruit, and occasionally some bugs off of each other. Perhaps your friend has been feeling a bit distant from the group lately: they’ve been getting a bit less food, a bit less attention. And then, as you’re both sat watching the early human world go by, they suddenly start making alarming snorting noises! Something must be wrong – perhaps they can’t breathe! Are they choking? And then – is that? Water is oozing, no, streaming out of their eyes! Doubtless your friend’s a bit alarmed by this too, but they seem to be just going with it. It’s quite moving actually…
OK, so it probably wasn’t quite like that. Our ability to cry probably came about much more gradually, making for a far less amusing anecdote. Evolution takes time, you see, especially for us humans with our long lifespans and the time it takes us to reach maturity: we’re no Drosophila melanogastar (that’s the humble fruit fly, darling of the genetics lab, to all you non-scientists). We evolve as a species so gradually with the passing of generations that we don’t even notice until a change has been present for a long time, and we can look far back into our history to compare how we used to be.
Humans were first technically able to produce tears purely for the purpose of cleaning the eyes – basal tears – quite early on, as lots of other less complex animals are also able to do this. It’s nothing particularly special; it’s just part of having eyes. It might interest you to know that there are three types of tears: basal, reflex (produced by a well-aimed poke to the eye, or by that meanest of vegetables: the onion) and then there are emotional tears, which as far as we know are exclusive to humans. So, why does liquid coming out of our eyes have anything to do with feeling strong emotion – why not some other behaviour? What was the reason for a connection being made – literally – between our tear ducts and the groups of neurons in our brains associated with our emotions?
Before we look at some ideas and get all excited and carried away with ourselves, it’s important to just bear in mind that while studies into questions like this are great and all, they can be difficult to draw proper conclusions from. It’s hard to truly mimic real life in a lab, and as you can imagine it’s quite difficult to induce true grief in a lab and then measure it (although, thinking back to A level chemistry practicals, I might be tempted to disagree…) Crying on cue is hard enough, let alone when you’re surrounded by a capering bunch of scientists, grinning as they eagerly clutch test tubes ready to catch your tears.
You might think that tears are just salt water, but actually they contain all sorts of chemicals, and emotional tears in particular are noticeably different from basal or reflex tears. They contain more protein; are loaded with hormones, especially those produced when stressed; plus a chemical called prolactin which acts on receptors in the lachrymal glands so that they carry out the brain’s command to ‘release the tears!’ So the chemicals in emotional tears are linked to the moods we feel when we cry. One theory, which I’d like to fondly call ‘flush theory’, suggests that crying is the body’s way of flushing out chemicals present from experiencing strong emotions. And to think the eyes are said to be the windows to the soul – perhaps ‘plumbing’ would have been more accurate, though definitely not quite as romantic. It’s a nice idea, which ties in satisfyingly with the feeling of release that often accompanies a good cry. However, from a physiological perspective it wouldn’t be the most effective way of getting rid of unwanted chemicals: even a long bout of heart-broken sobbing will only produce about a thimble-full of tears (the thimble, being of course an incredibly accurate and scientific unit of measurement).
Unless you’re a skilled actor, real tears are hard to fake. This means that they can generally be taken as a visual signal of real, genuine feeling and emotion. If you see someone crying they’re sending a sign that you should take their emotion seriously, and this is important for us as animals that have evolved to live in groups and form complex society. Crying puts you in a vulnerable state: in addition to being distracted from watching for predators due to the emotions you’re feeling, it also physically obscures your vision. So when you’re upset and someone comforts you, it’s a demonstration of trust and therefore incredibly risky from an evolutionary point-of-view: you’re laying yourself bare to the possibility that, rather than give you a pat on the back and pass you the tissues, your fellow human could just as easily kill you and steal all your food. When you’re upset and someone comforts you (if they choose the other option, I think it’s time to look for some new friends) it’s this sharing of trust which allows you to bond together more strongly – and this would have been an advantage for groups of early humans. Crying would have to provide some sort of benefit to outweigh its disadvantage, otherwise most of our weeping ancestors would have been pounced on by leopards whilst they stumbled about with blurred vision, and being human today would be an altogether much more dry-eyed affair. Because tears were potentially dangerous to the individual and so provided this momentary vulnerability to trust others with, it’s possible that this is why we cry when upset rather than, for example, ooze earwax, or wiggle our toes, or laugh or do any other weird alternative behaviour you care to dream up.
To other early humans, our ancestors might have looked a bit ridiculous at the time with their leaking eyes, snotty noses and melodramatic wailing, but on the whole they’d be closer and stick together knowing that they could trust one another to look out for each other. And just maybe, this could have been enough of an advantage that once the tears started, they were here to stay for the rest of human history.
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