Monday, May 7, 2012

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)

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