The zookeepers at Khao Kheow had never seen the like. Hundreds of people stood in line at the open zoo in eastern Thailand. But they ignored the elephants and brushed past the lions. A flock of ostriches drew barely a glimpse. Everyone was here for one reason: to meet Moo Deng.

Moo Deng is a baby pygmyUsed in names to describe animals and plants that are much smaller than more typical kinds. hippopotamus, born on 10 July. Almost immediately she became a social media sensation. Her name, chosen by a public vote, translates as "bouncy pig": an accurate description of her appearance and character. She has already inspired a makeup look and a cake.

She joins a long line of animals to go viral on the internet, from pocket-sized baby sloths to micropigs. Some have become celebrities, such as the American Grumpy Cat, famed for her scowling face, and the gay penguin couple Sphen and Magic.

The RedditAn American social news and discussion website. It has 1.66 billion monthly users worldwide. channel r/aww, which is devoted to pictures and videos of adorable furry animals, has almost 37 million followers. This obsession has even reached broadcast television. In 2015, the BBC aired a documentary called Super Cute Animals in which a presenter met baby foxes, giant pandas and a slow loris.

Our love for cute critters predates the internet, however. And it is not just for living animals. The Ancient Egyptians and Greeks created stuffed animals as both ritual objects and toys.

Kawaii - a Japanese concept similar to cuteness - originates from the phrase kawa hayushi. It means blushing as if in embarrassment, and has been used since the 11th Century. Today it is seen in wide-eyed manga characters and Hello Kitty merchandise.

In the West, animals have long been popular in art. George Stubbs and Louis Wain became celebrated for paintings of horses and anthropomorphisedSuggested that non-human things have human traits, emotions, and intentions. cats, in the 18th and 19th Centuries respectively. The German toymaker Richard Steiff created the first teddy bear in 1902, and books like The Wind in the Willows and Walt Disney's cartoons popularised the idea of animals who walk and talk like humans.

Cats have evolved from mere rat-catchers to much-loved household pets, while dogs, once used for hunting and herding sheep, are often now valued family members.

Whether living, stuffed or animated, some think we love cute animals for a reason. In 1943 Austrian biologist Konrad Lorenz proposed the "baby schema". Tiny humans and other animals look helpless. Nature is telling us to protect them.

American research scientist Daniel Kruger writes: "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."¹

Growth theorist Frances Richards believes this allows cute things to control us: "Professing its own... powerlessness, it gains power over and directs all interactions with it."²

Others think cuteness is not so predictable, and different people find cuteness in different places. Some are unmoved by kittens but love puppies. Old animals, such as tired donkeys or aged dogs, can be cute - as can unnatural, arguably ugly figures such as the alien ET or violent giants like King Kong.

Is there a science to cuteness?

Yes: All our behaviour is determined by biology and genetics. And our love for cuteness is no exception. We see big eyes and soft cheeks, sense helplessness, and want to protect them from danger.

No: Cuteness defies logic. In Africa, hippos kill more human beings than any other animal. Domestic cats torture and kill birds and mice. And yet humans cannot help but worship their cuteness.

Or... There might well be. But what is real is the cuteness contagion. As millions of cat videos shows, cuteness is a major cultural force - and one that seems able to bind people of all backgrounds.