• Question: Why do we cry when we are hurt or upset? There is absolutely no point in crying. The Job of the tear duct is simply to lubricate the eyeball, Not to make our face wet.

    Asked by yourmum to Pete, Meeks, Stephen, Steve, Tom on 18 Jun 2010 in Categories: .
    • Photo: Stephen Curry

      Stephen Curry answered on 18 Jun 2010:

      The job of tears (or the fluid that surrounds our eye all of the time) is also to prevent bacteria from starting an infection.

      But, you are right: there’s no ‘point’ in your eyes leaking when you are sad or upset. However, in our culture this has become a sign that communicates to other people that you are hurt or distressed. This type of physical expression is an important part of communication.

    • Photo: Steve Roser

      Steve Roser answered on 18 Jun 2010:

      Crying is obviously something that we do from very early on to get attention. Waaah! my nappy! But ‘tearing’ – the wet stuff – is a bit odd, as you say- there seems to be no real consensus on this except to point out that it is an emotional rather than a physical thing, and is some sort of signal. We cry tears when we are happy as well, most of us more often this when we are adults.

    • Photo: Marieke Navin

      Marieke Navin answered on 18 Jun 2010:

      For babies it’s a survival mechanism, it’s the only thing they’ve got. So perhaps it stems from that but I really don’t know!

    • Photo: Tom Hartley

      Tom Hartley answered on 18 Jun 2010:

      This is a “why” question which is always hard for science as I’ve mentioned in some of my other answers. I am going to give a general answer, because this is a really interesting question which might help explain what I mean. Maybe not.

      I think the best explanation, since crying is universal (everyone does it), is that this is a genetic trait that has evolved. There is no reason why such characteristics should serve one purpose. It certainly seems that a tear duct would lubricate your eyeball, and I would be surprised if this wasn’t a factor in the evolution of tears – creatures with dryer eyes might have to use more energy moving their eyeballs, and might be prone to infections (because it would be scratchy and because – I think – tears have an antiseptic property). Also the thin film of tears would slightly affect the optics of the eye, so perhaps that is also useful (I doubt it). Tears are visible on the face, and could be used as a social signal (e.g., to indicate sadness, pain etc.) so that other members of the “troupe” might help (sharing food, carrying a wounded member). All these things might under certain circumstances save a life, and thus help animals/early humans with tears out compete others, and survive to produce young. We can’t really be sure. But the different advantages of crying/tears would not conflict with one another, so there’s no reason why both couldn’t and shouldn’t evolve together using the same mechanism. Evolution has a way of using and reusing the same mechanisms and structures for multiple purposes, and we often come unstuck when we imagine a given feature is there for a particular reason. It’s just there (according to evolutionary theory) because it helped the animal’s ancestors survive, or came about randomly and didn’t do any harm.

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