Moo Deng, a baby female pygmy hippopotamus living in the Khao Kheow Open Zoo in Thailand, has recently pervaded all corners of the internet. Moo Deng, translated from Thai as “bouncy pig,” became viral when videos of her exploding in energetic temper tantrums, mischievously nipping at her caretakers and even occasionally accepting affectionate pats gained traction on social media platforms. 

Comments under posts featuring the viral star attribute Moo Deng’s fame to how undeniably adorable she is. As showcased by the internet’s reception of Moo Deng and the fact that 66% of U.S. households own a pet, people pay special attention to animals with particular physical characteristics that they categorize as “cute.” 

What does the research say about what makes these animals cute?

The prevailing explanation for cuteness is that people find the facial features of infants to be cute. Konrad Lorenz and Nikolaas Tinbergen introduced the idea of the “Kindchenschema,” or infant schema, which is the mental framework with which people perceive and categorize infants. The infant-like features that make up this framework are large, round eyes, full cheeks, a small chin, high eyebrows and a disproportionately large head, according to a study that obtained subjective ratings of adult male faces on physical dimensions and “babyfacedness.” 

Another study manipulated facial dimensions using Adobe Photoshop on images of human adults, human babies, dogs, puppies, cats and kittens to be either “high infantile” or “low infantile” and assessed how participants interacted with the doctored images. Researchers found that participants rated “high infantile” faces as cuter than “low infantile” faces. This finding is consistent across all species, meaning that people use the infant schema to perceive animals that are not human.

However, the infant schema is not limited to just facial features. An experiment measuring the effect of personality on perceived cuteness found that adults’ change their perception of infants after learning their temperaments, such that happy infants were viewed as cuter than sad infants. Therefore, it is possible that infantile behaviors, such as when Moo Deng pouts in retaliation, also activate the infant schema.

Simply put, the reason behind Moo Deng’s precipitous claim to fame is that she resembles a baby. But why might it serve people to be able to identify a baby as cute?

Perception of cuteness is accompanied by a strong physiological reaction. Cute things rapidly activate the orbitofrontal cortex, a brain region associated with emotion and pleasure. Adults exhibit increased facial muscle activity in muscles that are involved in happy facial expressions when presented with infant photographs compared to when presented with non-infant photographs. Adults, regardless of sex and whether or not they have had children, spend a longer time viewing infant faces than they do viewing adult faces.

Scientists theorize that people exhibit this preference towards cuteness because babies need constant attention in order to survive and grow. People are programmed such that cuteness activates their parental instincts, prompting a wide range of behaviors from a variety of humans — from a parent endlessly doting on their children to a netizen expressing their undying devotion to a two-month old hippo from Thailand.

A version of this article appeared on p.15 of the Oct. 3, 2024 edition of the Daily Nexus.