What do onions, the Titanic, and 13-year old heathens have in common? They can all make you cry. The onion will make any animal with eyeballs tear up. But only Homo Sapiens will cry when Jack sacrifices himself for Rose (he didn’t actually need to) or because your 13-year old niece/nephew calls you fat. No other animal cries for the reasons we do (or at least the ones we’ve been able to study in the lab don’t).
This begs the question, why do we cry?
Types of tears
Humans produce a lot of tears (or eye water). The lacrimal glands, the glands responsible for your Eyeagra Falls (I am ashamed of this, but I love it too much), produce up to 57 to 114 litres (15 to 30 gallons) of tears per year. That is approximately 114 to 228 bottles of bottled water (the 500 ml or 16.9 oz). That’s a lot of water. All this fluid isn’t only for those rainy days.
There are three types of tears:
Basal tears are present 24×7, 365 days, forming the largest portion of the three types. They play an important role in keeping dirt and debris off the iris at all times.
The first category is basal tears. The lacrimal gland in the eye produces a large amount of these tears every day. By a large amount, I really do mean a lot. More specifically, 132 kg/ year.
However, once you understand their function, you can see why they are produced on such a large scale. They play an important role in keeping dirt and debris off the iris at all times.
The eye is actually surrounded by 3 different layers of basal tears.
The first layer is the mucus layer, which keeps the other two layers fastened to the eye. The second layer is the aqueous layer, which is responsible for keeping the eye hydrated. It even repels invasive bacteria and protects the cornea from getting damaged. The final layer is the oily lipid layer, which makes sure that the surface of the iris is smooth, giving you the high-definition vision that you enjoy. The lipid layer also prevents the aqueous layer from evaporating.
“Are you crying?”
“No. Something went in my eye.”
These are reflex tears. These tears come to the rescue only when irritants, such as dust particles, hair, or sand, threaten to pose a real risk to the cornea. Sulphenic acid is by far the most potent out of all these irritants. Chopped onions produce release it by the bucketloads, making one cry.
The brain notices the external threat and signals the lacrimal gland to increase its tear production. The industrious lacrimal gland upgrades the basal tears into reflex tears by stuffing them with antibodies to fight any incoming harmful micro-organisms. The lacrimal gland almost always ends up creating waaaay more tears than it needs to wash away the irritants.
“Are you crying?”
“No way! Something just went in my eye, that’s all,” she said as Jack sunk to the bottom of the Atlantic ocean.
The cause of emotional tears is in the name itself. Certain emotions like sadness, joy, anger, or when something gives us the ‘feels’, trigger crying. They are a curious phenomenon unique to human behaviour. No one has recorded an animal other than humans crying because Mufasa died.
When exposed to a highly emotional stimulus, the amygdala takes note of the emotions and sends the signal to the hypothalamus, which in turn alerts the sympathetic nervous system. The SNS then notifies the lacrimal gland to begin the waterworks. The sympathetic nervous system is also responsible for the fight-or-flight response; therefore, we also see other reactions while crying, such as an increased heart rate and slower breathing.
If emotional tears are only seen in human beings, what function do they actually serve?
Well, for one, they are an effective form of communication.
For example, we all know that babies cry in order to communicate their needs. And as adults, we still do the same thing. We cry as a social mechanism to display sensations of submission or helplessness, which often elicits sympathy from others.
Human beings are social creatures and crying helps us bond with everyone around us, letting them know of our need for a more comforting environment. Even tears of joy are effective at strengthening our feelings of group bonding.
Another reason that emotional tears exist is that they help us relieve stress. No, that’s not just a metaphor or an emotional explanation – they literally shed stress. Emotional tears appear to contain high levels of stress hormones, such as ACTH and Leucine Enkephalin (a natural painkiller). By crying, you’re basically eliminating all the stress from your body! Maybe that’s why we always seem to feel better after a good cry.
Why did we start crying in the first place?
From an evolutionary perspective, we aren’t sure why humans evolved crying and not other animals. Charles Darwin who had an explanation to human hairlessness, had this to say about our propensity for tears, “We must look at weeping as an incidental result, as purposeless as the secretion of tears from a blow outside the eye.”
There have been many theories to why we have tears. One popular theory is the attachment theory proposed by psychoanalyst John Bowlby and his colleague Mary Ainsworth. This theory proposes that crying is an adaptation to foster attachment between child and parents which prevails in adult human relationships as well.
In his book, Why Only Humans Weep, Ad Vingerhoet suggests crying replaced screaming and other vocal pleas during infancy. Babies screaming for attention could alert predators to their location. Since a human infant is in close proximity to their caregivers, more visual cues to attract attention would suffice.
Vingerhoets further explains that human brain development takes much longer (up to 25 years) than other animals. Human young remain more vulnerable longer which is why we’ve carried along with crying.
With all these theories, there isn’t enough to prove why we cry. It is difficult to explain all the reason we cry, from heartbreak to when we are hungry with one sole explanation.
But tears aren’t only used to communicate distress. Emotional tears are directly responsible for calming you down, as well as signalling others to provide you with attention and empathy as a result of your unstable emotional state. Although you might not believe this, tears are quite healthy for your mental well-being, so don’t you dare hold them back!
In case you are curious if animals cry, click here.