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It's really cute.

But what is cute, scientifically?

I mean, why do we like soft, cuddly things

and why do cute things have a unique effect on us?

Well, the word cute is a shortening of acute,

which originally meant "keen," "shrewd," "perceptive."

About 180 years ago, the word cute began to be used as slang for a girl, who was pretty.

And after that, it accrued a new meaning

and was used to describe cuddly, delicate, quaint, precious, youthful traits.

Konrad Lorenz studied cuteness in living things

and put together a great specific list of what we consider cute.

Small body size with a disproportionately large head,

large eyes, and round and soft body features.

But why exactly did these characteristics elicit an "ooooohhh" response from us humans?

Well, Lorenz pointed that you could find all of those characteristics in the human baby,

which makes sense.

If merely looking at our offspring makes us instinctively feel protective and nurturing, well, that's great for all of us.

A fun consequence of this is that our experience of cuteness

can be triggered by things that aren't human babies.

For instance, shells, bunnies, owls and even a hammer.

A hammer, how can that be?

Take a look at this interactive tool from the Exploratorium.

A hammer is boring.

But if we apply Lorenz's traits and make it really round and really squat,

it goes from a utilitarian tool to a cute little tiny hammer.

Oh, he's just a little hammer, don't hurt him.

It is a hammer that has become cute,

because we gave it qualities that we see in our own offspring.

As Daniel Dennett puts it,

"if human babies looked like this, instead of that, we would find this cute."

And whenever we saw something that looked like it,

we would wanna cuddle and snuggle with it.

Alright, so we have a pretty good idea about the how and what of cute.

But where is cute?

Well, researchers have shown cute baby pictures to subjects

while using functional MRI to track activity in the brain.

And sure enough, the cuter the baby in the picture, the more activation found right here --

the nucleus accumbens. A pleasure centre.

When activated, the nucleus accumbens releases dopamine.

It's all part of our internal reward system.

It's the same part of the brain targeted by cocaine and meth.

Cuteness is such a powerful force on the brain

in fact that it can affect our behaviours -- what we like, what we buy.

And so it's no coincidence that the creators of cartoon characters,

like Mickey Mouse or Pikachu,

have drawn them more and more cute over time.

The Japanese concept of Kawaii is a great example of this

and it's one that's fun to quantify.

If you're an adult, how many of your own heads, stacked on top of each other,

do you think it would take to equal your height?

The answer for most of us is around 7.5.

But illustrations of people that are meant to make them look heroic or noble

tend to make the person around 8 to 8.5 heads high.

Cute goes the other way.

Manga characters tend to only be about 5.5 to 6.5 heads tall.

Back to babies.

There are many other psychological factors at work

that cause us to want to instinctively take care of our young.

And to be sure, some of them are decidedly not cute.

For instance, poopy diapers.

Researchers have found that mothers, when exposed to soiled diapers,

tend to consider the smell coming from their own child's diaper to be the least terrible,

despite not knowing which diaper belonged to which kid.

When something retains juvenile traits all the way through adulthood, it is called neoteny.

And we love it, especially in animals that we keep as pets.

Of course, us humans have selectively bred all kinds of animals

to make each generation more and more useful to us.

But the dog may be the animal that we have spent the most time designing,

making each generation better at hunting or better at staying cuter for longer.

Dogs like this have been designed by us to look, grow and behave in ways that we want.

Not that dissimilar from how we would design, say, a DVD player and its features.

So whether it's staying cute forever or just being a really great hunting companion,

the modern dog, more than any other animal,

could be considered not so much a consequence of nature

as much as it is a piece of human technology.

As Science Friday puts it,

"the dog is man's best friend because it may be man's best invention."

So go pet a cute dog today.

And as always, thanks for watching.