Why does the internet love baby hippo Moo Deng? There’s a science to it.

Her skin is always moist and her cheeks pink and peachy. She’s usually seen nibbling at her caretakers’ knees, running around her pen - belly rolls jiggling - or opening her mouth in an apparent scream.

It’s Moo Deng, the baby pygmy hippo that has become the internet’s latest obsession.

Since she was born in July in Thailand’s Khao Kheow Open Zoo, Moo Deng - whose name roughly translates to “bouncing pig” or “pork patty” - has reached viral stardom. So far, she’s been meme-ified by the Utah Jazz NBA team, turned into an eerily lifelike cake by a Bangkok bakery and inspired a dewy pink makeup look by Sephora Thailand. She also has her very own Wikipedia page.

But what seems like unlikely celebrity has a simple, if surprising, explanation, according to scientists.

Moo Deng and other baby animals spark adoring reactions worldwide because their cuteness hijacks our brains, studies show. The animals’ human baby-like features strike at people’s ingrained nurturing instinct - something scientists think is an evolutionary trait that has allowed the human species to survive across millennia.

“When we see these infantile features - those big eyes, large foreheads, small chins and pudgy bodies - we interpret that as helplessness and as dependency, and it motivates us to care for them,” said Daniel Kruger, a research scientist in evolutionary psychology at the University of Michigan and the State University of New York at Buffalo. “And it’s so powerful that it happens across species.”

In 1943, Konrad Lorenz, an Austrian ethologist and biologist, first proposed the concept of the “baby schema,” or the blueprint of features that induce our cuteness perception. Since then, a multitude of research has confirmed that humans gravitate toward these universally appealing qualities of chubby cheeks, stubby noses, small bodies and big eyes.

A study published in 2009 found that the “baby schema” triggers both men and women’s motivation for caretaking. That cuteness, another study found, affected adults even if they were not parents themselves.

According to Morten Kringelbach, a University of Oxford neuroscience professor, the cuteness overload “is more than something purely visual.” Seeing something adorable rapidly ignites activity in the regions of the brain that are linked to emotion and pleasure. This might be the reason babies and cute animals quickly grab our attention and are so hard to ignore, he wrote in 2016.

It’s also why cuteness might be key to babies’ survival, said Kruger. By tugging at people’s heartstrings with their adorable - albeit somewhat alien-like - traits, babies inspire in humans a desire to hold, cuddle and take care of them. In fact, research has shown that the cuter an infant is perceived to be, the more likely they are to be adopted and receive baby talk from adults.

“Humans in particular, we’re strongly selected to have these caretaking reactions to cuteness just because our infants are so helpless - just imagine at what age a child would actually be able to fend for itself if there were no adults around,” Kruger said. “So we really need to have these really strong caretaking reactions for our own survival, and we tend to interpret or project this onto other species.”

Kruger has tested this cross-species phenomenon in his research. In a study, he showed participants photos of recently hatched birds and reptiles. The infants belonging to four semi-precocial animal species - or those that require parental care - were rated higher in attractiveness, cuteness and helplessness than those belonging to super-precocial animal species - or animals that don’t require parental care. These semi-precocial birds and reptiles also sparked greater nurturing reactions, with people saying they were more likely to want to hold them and adopt them.

“This is the same reaction people are having when they see zoo animals - and well, now this baby hippo,” Kruger added.

David Barash, an evolutionary biologist and emeritus professor of psychology at the University of Washington, also said the “baby schema” could help explain why Moo Deng’s clumsy antics - whether it’s twitching in her sleep, showing off her tiny teeth or generally being dramatic - have become inescapable online.

It also may explain why the zoo’s visitors have more than doubled since Moo Deng became an internet sensation, according to Narongwit Chodchoi, director of Khao Kheow Open Zoo in Chonburi province.

“Her stubby nose, large eyes, very inconspicuous ears, and her body being sort of relatively contained are appealing,” Barash said. “And it actually might be why hippos are so popular and seem adorable even when they’re adults - despite the fact that hippos in Africa kill more human beings than any other vertebrate.”

The “baby schema” has long pressed adult humans into indulging babies and even breeding dogs that have the qualities they find so endearing, Barash said. But apart from her baby-faced charm, other psychological factors might be at play when it comes to Moo Deng’s stardom, he posited.

For instance, there’s fame’s “snowball effect,” Barash said, or how “once interest in almost anything passes a certain threshold, it feeds upon itself - sort of how the Kardashians are famous for being famous.” And there might also be something about how humans have an unescapable attraction to the miniature versions of things - be that a pony, a tiny dog or a microscopic purse, he said.

To that end, he added, Moo Deng seemed poised for fame. Pygmy hippos, which are native to the swamps and forests of West Africa, are like a mini version of its larger relative and only reach about half the height of a full-size hippo, or up to three feet.

But pygmy hippos’ cuteness hasn’t been able to guarantee their survival. The combination of habitat loss and poaching has nearly driven the species into extinction, with only about 2,000 animals left in the wild.

That’s something Barash said he hoped Moo Deng’s newfound internet fame could help assuage.

“It’d be nice if people could extend their interest in this one little critter to the species in general,” he said. “So it’s one thing to find it cute, but it’s another thing to maybe try to extend that to helping and to protecting not just this one critter, but to all of its relatives.”