The zookeepers at Khao Kheow had never seen such big crowds. 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 regularly coos 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.

Our love for cute critters predates the internet. The Ancient Egyptians and Greeks created stuffed animals as both ritual objects and toys. 

The early 20th Century saw the start of our modern idea of cuteness. In 1902, the German toymaker Richard Steiff created the first teddy bear. Books like The Wind in the Willows and Walt Disney's cartoons made us fall in love with 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.

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.

Yet others think cuteness is more complex. People find it 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. 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.