In this episode, Aleena and Janine get stuck into the research around human crying. Why do we do it? How did this bizarre behaviour even evolve? Why are humans the only animals shedding tears due to emotion? Should we hold in the tears or let them flow? Meanwhile Aleena then shares her newfound appreciation for protective eyewear for doggos and Janine explains how she is attempting to keep her new mobile phone for more than 5 years and nerds out about battery science!
Why is it only humans that shed emotional tears?
Check out this awesome review paper and Janine’s summary below: Gračanin, A., et al. (2018). Why Only Humans Shed Emotional Tears. Human Nature, 29: 104-133.
Many animals produce tears in response to any assault to the eye, such as physical or chemical exposure. These so called ‘reflex tears’ provide a protective effect. We have all experienced these reflex tears – onion crying anyone?! But crying as a result of emotional change – that has only been conclusively observed in humans. How interesting!
Crying in humans kicks off from birth and past research has shown that a big reason why infants cry is to maintain attachment with caregivers. This is really important for human babies in particular as they are particularly powerless and helpless, when compared with infants of other species. A loud vocal signal can alert caregivers any time, day or night. Interestingly, infant crying starts off as a purely vocal signal, and the tears don’t actually show up until a bit later. And then as we get older, the vocal aspect of the crying reduces significantly, yet the tears remain or increase… but why?
Tears do seem to provide information that we can’t otherwise transmit via facial muscles alone. In one study, participants were shown pictures of crying adults, but the tears had been digitally removed from the photos. Participants had a lot of trouble working out what emotion was being shown! And another study has shown that humans can recognise that someone is sad within 50 milliseconds of seeing tears.
Tears in adults seem to be functioning as an ‘honest signal‘ – this is a feature that has evolutionary benefits for both the sender and the receiver, and it looks like tearful crying in adults promotes social bonding and social cohesion. Crying signals distress or helplessness and encourages sympathy and care from others in the group, and quiet tearful crying, as opposed to loud crying, is less likely to annoy others and lead to aggression. Imagine scream crying in a work meeting – it probably wouldn’t go so well! Less is known about why we sometimes cry when we’re all alone, but perhaps it’s because we usually tell someone about it later (check out this ABC News piece for more).
So if crying is so useful, why don’t we see it in other species? This may be due to the extreme neoteny in humans in general. This is a tendency for baby-like features to be maintained across the lifespan, as compared with other primates. It is possible that older children that cried with tears had some survival advantage over those that did not. And similarly, in adults, crying tears maybe conferred some sort of survival benefit. Our capacity to shed emotional tears, and to take in the meaning of emotional tears in others, is very much tied in us being a highly social species and is likely to have helped us to become the successful species that we are today.
Let the tears out or keep them in? It depends on where you live…
Crying is an evolutionarily important behaviour and everyone will feel the need to cry at times, but culture has an important impact on crying tendency. This study takes a look at how crying tendency at the country level is linked to different characteristics of countries. It seems what’s really driving crying at the country level isn’t so much about the level of distress in counties (like economic distress), but more whether crying is enabled or is accepted according to a country’s social norms…
What brought out our inner square?
Janine hates ‘planned obsolescence’ so much that she will do whatever it takes to defy it – mwa hahaha! Janine managed to push her last mobile phone’s lifespan to over 5 years. Can she push the new one even longer? By better understanding how the newer lithium phone batteries degrade over time (see here and here and here), and downloading a specific app that is based on science and ensures optimal battery charging schedules, she will give it a red hot go!
Meanwhile Aleena discovered that dogs are not only good boys, but waaaay cool boys. Her hysterical encounter with a goggle wearing hound has led to newfound knowledge of the market for eye protection for one’s precious pooch. Gimmick or not, we defy you not to enjoy all the internet images of eager goggle-wearing dogs and their variable life adventures.