The Ugly Cry Face

The human body is an immensely complicated thing. Each organ and bodily fluid has at least one, if not multiple functions. From your eyelashes to your toenails, humans have evolved to thrive in their surroundings. This includes tear production and the act of crying, which has its obvious perks: protection and lubrication of the eyes, delivery of important nutrients and electrolytes to the cornea, the removal of irritants. Additionally think of the great relief a sobfest can bring at the end of a hard day. The latter refers to “emotional tears”, which act as a sign of emotional distress. For decades scientists have tried to determine why it is we cry, linking it to sadness and signals of harmlessness. Randomized trials have been conducted to determine whether tears elicit a change in mood or increases empathy. These responses make sense to us because of our own personal experience with crying. But then came Dr. Sobel at the Weizmann Institute of Science in Israel, and the world of emotional tears has never been the same.

In 2011 Dr. Sobel's research group published an article where they reported that emotional tears from women elicit a seemingly odd response in men: reduced arousal and sexual attraction. To conduct this research, the scientists had women watch sad movies and collect their tears, this way the tears would be of the emotional kind. As a control, the women were also asked to trickle saline solution down their cheeks and collect the drops like they did their own tears. Men in their mid to late twenties then were asked to smell either the tears or saline and perform different tasks. One of these tasks involved looking at pictures of women like the ones below and rating their sadness and attractiveness. 

Men who were smelling tears were not any better at rating a woman's sadness compared to the men that were smelling saline. They were, however, less attracted to the female's photo. The researchers attributed the men's inability to rate sadness to the fact the men themselves were not sad. Therefore, the researchers repeated the study but first had the men watch a sad movie. Instead of asking the men to rate a female's attractiveness they measured their arousal through both self reports and proxy measurements (heart rate, skin temperature, respiration rate, among others). Salivary concentrations of testosterone were also measured. Again, the men that smelled the tears had decreased levels of arousal - both self reported and measured - as well as a decrease in salivary testosterone concentrations. Interestingly, even after watching a sad movie the men that sniffed tears did not report any differences in mood compared to the men that smelled saline. If tears contain a chemical signal that elicits sadness or empathy, the tears should have made the men more sad than the saline, yet this result was not achieved. 

Finally, to be sure that what they were seeing was a true effect, the scientists asked the men to watch an "erotic film" while they conducted brain imaging. This last portion of the study probably made for some awkward social interactions, and conjures up the image of a mad scientist creepily studying his subjects from behind a one-way mirror. Nonetheless, areas of the brain that "lit up" while viewing an erotic film had reduced activity when the men sniffed the tears, again indicating that a woman's tears reduce sexual arousal in men. 

While this study may leave us with more questions than answers, it does give us some insight into the evolutionary reason for tears. Seeing someone cry may still very well be a visual sign of sadness, but the chemical signaling compounds in tears do not seem to change the empathetic response. Now the question turns to why it would be beneficial to reduce arousal in times of sadness, and whether we would see a similar result if we were to reverse the genders or change the age group. 

Perhaps crying was the original, ahem, excuse. As in "I have a headache..." type of excuse. You get my gist. 


S. Gelstein et al. Human Tears Contain a Chemosignal. Science (2011)

The Evolution of Cuteness

It’s one of my favorite stories in science: why we are programmed to think our babies are so damn cute. Besides giving parents bragging rights and feelings of pride and adoration, having our brains programmed to think our offspring are cute comes with evolutionary advantages. To better understand what those advantages are we will need to take a step back into the times when our ancestors were still spending most of their days swinging from branch to branch rather than running around on two legs. We needn’t be too imaginative, just think of how an ape moves around. Most of its time (when not adorably hanging around) is spent on 4 limbs. This means the joint between the hip and the upper femur doesn’t need to be able to bear a lot of weight. Because of this, the shape of the pelvis of an ape was, and still is, very different from the pelvic bone of a human. 

About 6 million years ago, the early human ancestors came down from the trees and began to discover all that the grasslands had to offer. Why? I think they were probably just sick of eating tree fruits all day and craved adventure! Due to this drastic lifestyle change, the skeletal structure of early hominids began to change as well. The hip began to adjust so that all of the body weight could be put on only two limbs for a significant amount of time. As the hip evolved to be more compact, so too did the birth canal which narrowed to give more strength to the hips for bipedalism. A smaller birth canal would be okay for your monkey-brained neighbor, but not for the superior intellect of yourself. As we went from apes to hominids the brain and the head size began to develop as well. This poses an obvious problem in human evolution: how on earth are we supposed to give birth to babies with increasing brain and head sizes while at the same time develop a narrowing birth canal? 

Schematic drawing of the birth canal sizes and fetal skull sizes in apes and humans. Looks like humans have it pretty bad!

An interesting conundrum, and one we have thankfully overcome! If you have spent any time around a newborn you know how completely helpless they are. Newborns need a more capable being to help them eat, burp, even hold their head up. Given that the size of human brains are substantially larger than other mammals that are completely capable upon birth, does this not strike you as odd? Additionally, consider the length of gestation for us humans. Nine months is a relatively long time, especially when the end product isn’t quite ready for life on its own. While fetuses are in the womb their brain and head size will develop to be as big as possible while still small enough to pass through the narrow birth canal. Then, after birth, the baby’s brain will continue to grow as the baby becomes more able to perform tasks like eating and holding a spoon. The soft connective tissue, or fontanels, connecting regions of the skull at birth will eventually fuse when the skull has reached its proper size. For quite some time after birth however, infants are dependent on others to help them survive. Without this help, infant survival would be impossible.

Enter the cuteness factor! Lucky for all of us parents have a natural affinity for their offspring when they are brought into this world because they’re perceived as cute! The baby fat, the forward facing, large round eyes and button nose all contribute to why we think infants (and some baby animals for that manner) are cute; and part of the reason why parents feel a compelling need to stick around and care for them. This has been given the technical, German term of Kindchenschema, roughly meaning childlike cuteness in some scientific literature. Interestingly enough, the ability to correctly select the “cuter” baby when presented with a cute and a less-cute picture of a chubby-cheeked test subject is stronger in women (see the photos below for an example). Perhaps Kindchenschema is another way, in addition to the oxytocin release women experience while breastfeeding their newborn, that the maternal instinct shapes new moms. 

Because cuteness makes something click in the parents’ brain causing them to want to care for the infant, the baby is given time to develop its brain and fuse its fontanels. Of course there are other theories of why newborns are seen as cute, one of which is simple natural selection. As the the theory goes, the children that were seen as the cutest got more food, love and attention from their parents, thereby growing up to be strapping, fertile adults that could pass along their cute-genes to their own plethora of offspring. This is a noteworthy theory, but I like to think that the evolution of cuteness derives from the infant’s need for love and attention right at birth. So in the end, when humans started to walk around and gather their food, babies started finding out a way to make us unconditionally love them. Those maniacal babies!  

Insert devious laughter here. 

1. Rosenberg, K. & Trevathan, W. Birth, obstetrics and human evolution. BJOG (2002)
2. Lobmaiera, JS. et al. Female and male responses to cuteness, age and emotion in infant faces. Evolution and Human Behaviour (2010)