its own thin slice of the fullness of reality

that it can detect.

Evolution has shaped the senses of animals

according to their needs,

but no animal can sense everything.

No animal is perfect at everything.

There is so much information out there

that to be able to detect it all

would be an overwhelming experience and also unnecessary.

There's also a cost to the senses.

Senses don't come for free.

To build a sense organ and to maintain all the neurons

that feed into that sense organ takes up a lot of energy,

which is why their senses are so refined

and so constrained by their evolutionary needs.

So the word umwelt was popularized and defined

by a German zoologist named Jakob von Uexküll

in the early 20th century.

It comes from the German word for environment,

but he meant the animals' sensory environment.

And that's the specific set of sights, smells, textures,

and sounds that that animal has access to

and that another animal might not.

When you really think about the senses,

you do start to understand the very different kinds

of information that those senses offer their owners.

So we obviously taste with our tongues,

but a catfish is essentially a swimming tongue.

It has taste buds all over its skin.

If you put little pieces

of food near the flank of a catfish,

it will be able to taste it

and turn around and snap it up.

For most animals, taste is about food.

It's about trying to work out whether something

is worth eating or not.

And for humans, food is something that we put in our mouths.

But if you are a very small animal,

food can be something you land on.

And which is why for many insects taste buds

are some things that are found in their feet

as well as in their mouths.

A fly landing on the apple that you are trying to eat

can taste it just by walking on it

before you put it in your mouth.

I, like most of you, have two eyes.

They sit in the front of my face and they point forwards,

which means that my visual world is always in front of me

and I walk into it.

But most birds have eyes on the sides of their heads,

which means their visual world is around them.

They often have close to wraparound vision,

seeing to the sides and also a little bit to the back.

And that kind of wraparound vision

is really hard to wrap your head around.

And then of course there are changes

that can occur over an animal's lifetime.

So the umwelts of an adult

might be different to the umwelts of a juvenile.

Jumping spiders are very driven by vision.

They have excellent eyes.

But those eyes also become more sensitive as they get older,

more sensitive to light,

which means that I think the world of a jumping spider

will get brighter as it ages.

One scientist describe this to me

as a jumping spider watching the sun rise as it gets older.

So a sea otter has very sensitive paws.

They don't look very sensitive.

They look like these weird sort of cauliflowery mittens.

They have a sensitive touch that is equal

to our exquisitely sensitive fingertips.

One of the key differences

is that they are also extremely skilled

at using that sense of touch.

They're very fast about making touch-based decisions.

A sea otter will dive down into the ocean

and very quickly root around with its paws.

It will grab that sea urchin, yank that clam,

and then rise to the surface before eating its food.

A sea otter doesn't have the benefit of blubber

that a whale or a walrus might have.

It has very thick fur, but it can find enough food to eat

because it has not only very sensitive hands,

but very fast hands too.

Even in a completely dark room

where the very large eyes of an owl

might not be of much use,

they can still hear and they hear really well.

The dish of feathers around an owl's face

that gives it that distinctive owl-y look acts as a radar

dish funneling sound towards its ears.

Those ears are incredibly sensitive,

but they also have a unique trick

that allows the owl to work out exactly

where sound is coming from.

Based on when sound arrives in my ears,

where those first arrives at the left or the right,

I can tell where a sound is coming from

in the horizontal plane.

I can't do that trick in the vertical very well

because my ears are level with each other

so sound arrives at both of them

from above or below at the same time.

An owl solves this problem because its ears are offset.

So they're asymmetrical.

So one ear is slightly higher than the other.

And when sound arrives at that ear first,

the owl knows where in the vertical plane it's target is.

And that's why an owl in the dark

can land exactly on a mouse.

It's why owls in the wild can bust through snow

to pick up scurrying rodents that they couldn't even see.

One of the primary uses of scent in the animal kingdom

is for navigation, for finding your way around a landscape.

You know, my dog, Typo, absolutely can do this.

He knows where we are by cross-referencing his memories

of the smells of the neighborhood

against what he's smelling at any given moment.

But there are other animals that use scent for navigation

in even more extraordinary ways.

A lot of sea birds, the group known as tubenoses,

use the odorscapes of the ocean to find food.

The ocean looks featureless to us, right?

We can glide over it

and just see this endless expanse of uniform blue,

but it's not featureless to an albatross.

Underwater features like mountains

and valleys leads to concentrations of nutrients,

which then concentrate food, plankton, and then krill,

the kinds of things that a seabird might eat.

And so the ocean has this undulating odorscape:

odors that reveal the concentration of possible food

and then areas of no scent that reveal scarcity in the deep.

Elephants can do this too.

Elephants can navigate over long distances.

Obviously, they have that trunk.

They have constantly scanning about

with this extremely elongated nose.

You know, they'll react to the imminent arrival of rain.

People have suggested

that they can find buried sources of water by smelling it.

It's quite difficult to understand exactly

how elephants smell

because they are large, intelligent animals

that are difficult to work with.

Part of this relies on us using our imaginations

like watching their incredible behavior,

looking at their trunk,

and trying to just make educated guesses

about what their olfactory world might be like.

There's a wonderful quote by Marcel Proust

that I think captures what's magical

about the umwelt concept.

He said that the only true voyage

would be not to visit strange lands,

but to possess other eyes

to see the hundreds of universes that each of them sees.

That's how I think about the sensory worlds

of other animals.

I think that when I get to empathize

with the smell world of a dog

or the touch world of a sea otter,

I feel like I'm traveling,

like I'm leaving the confines of my own body

and my own lived experience

and going on this fantastical voyage

into the world of another creature.