字幕表 動画を再生する 英語字幕をプリント Whether it is during a sad movie you swore you would never tear up in, or a heart-wrenching break-up following your first love, crying may seem like a strange physical response to your emotional turmoil. Why do we start the waterworks when we feel really sad? Is there a biological advantage or purpose other than washing your face or streaking your mascara? Well crying does not only happen when you are emotional, there are actually three types of tears. Basal tears are perpetually lubricating your eyes keeping them from drying out, while reflex tears act in response to an irritant like onions or dust. They begin a chain reaction releasing hormones from the brain which then trigger a tear response from the glands in the eyelids. And these tears help to get rid of the irritant. But tears of sadness? Strangely this leaky face phenomenon is exclusive to humans with a couple different theories as to why. And one is strikingly similar to the reason we blush, which we described in a previous video here. In many cases emotional tears are able to act as a signal to others of our genuine sadness or distress. That is not always easy to fake. Your tears blur your vision, essentially handicapping any aggressive or defensive actions sending those nearby a signal of need appeasement or attachment. From an evolutionary perspective, this increases communication with those close to you and ultimately your chance of survival. Some experiments have even taken photos of people crying and made copies with the tears digitally removed. Not surprisingly, people rated the pictures with tears to be more sad, while the ones without were often confused with puzzlement, awe or other expressions. But what about tears of joy? Well perhaps they are not so different, afterall tears of happiness may still be used as social signals for how we feel, and are thought to strengthen bonds between people. Also both emotions see activity in similar regions of the brain, such as the hypothalamus and basal ganglia which just happen to be connected to your tear glands. Another theory suggests that crying is one of your body's mechanisms to literally shed your stress. Interestingly reflex tears and emotional tears have very different compositions. Emotional tears have much higher levels of proteins, in particular some called adrenocorticotropic hormones which are linked to high stress levels. And some say crying helps to release these stress chemicals from the body, but the research here is limited and not yet conclusive. So go on, have a good cry, let the world know how you feel and potentially let out that stress. Got a burning question you want answered. Ask it in the comments, or on facebook and twitter. And subscrice for more weekly science videos.