Question: Hi everyone! I'm very keen on science but i've always wanted to know why do we cry. Do you know why?

Robert Hampson answered on 11 Nov 2014:

We cry, because we are sad, or because we are chopping onions, or because we stubbed our toe. Why do you cry?

What biologically causes crying or what evolutionary circumstance caused crying is a slightly different question. Most animals cry to clear dirt and gunk and stuff from their eyes. Tears also act as a lubricant for the eyelids (so they don’t scratch your eyes on the way up and down). Tears also kill bacteria and viruses to protect your eyes from infection. Tears in terms of rolling down your face because you are emotionally stressed is different to normal production of tears. The best theory at the moment is that when very emotional or stressed, we find it very hard to communicate. Tears provide immense benefits to social creatures like humans as it communicates our distress to people who can help us. I believe its the same reason that frowning and smiling are instinctive behaviours not learned ones. Honestly showing our emotions and conditions to those around us seems to be beneficial.