The zookeepers at Khao Kheow had never seen the like. Hundreds of people stood in line at the open zoo in Thailand. But they ignored the elephants and brushed past the lions. 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". She has already inspired a makeup look and a cake.

She joins a long line of animals to go viral on the internet. It coos regularly over cute creatures, from pocket-sized baby sloths to micropigs. The RedditAn American social news and discussion website. It has 1.66 billion monthly users worldwide. channel r/aww, devoted to pictures and videos of adorable furry animals, has almost 37 million followers.

But our love for cute critters predates the internet. 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. This means blushing as if embarrassed. Today it is represented by manga characters and Hello Kitty merchandise.

The German toymaker Richard Steiff created the first teddy bear in 1902, while 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 from harm.

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

Others think cuteness is not so predictable. 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 too - 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. 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. 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 show, cuteness is a major cultural force - and one that seems able to bind people of all backgrounds.