Sloths! The strange life of the world's slowest mammal

Sloths have been on this planet for more than 40 million years. What's the secret to their success? In a hilarious talk, zoologist Lucy Cooke takes us inside the strange life of the world's slowest mammal and shows what we can learn from their ingenious adaptations.

Hello.

Well, I'm here to talk to you
about my animal muse:

the sloth.

(Laughter)

I've been documenting the strange lives
of the world's slowest mammal

for the last 10 years.

I still remember the first time I saw one.

I was fascinated by their freaky biology.

I mean, what's not to love
about an animal that's born

with a fixed grin on its face?

(Laughter)

And the need to hug.

Audience: Awww.

But sloths are massively misunderstood.

They've been saddled with a name
that speaks of sin

and damned for their languorous lifestyle,

which people seem to think
has no place amongst the fittest

in the fast-paced race for survival.

Well, I'm here to tell you
that we've got this animal all wrong --

and how understanding
the truth about the sloth

may help save us and this planet
we both call home.

I traced sloth-based slander

back to a Spanish
conquistador called Valdés,

who gave the first description of a sloth
in his encyclopedia of the New World.

He said the sloth was

"the stupidest animal
that can be found in the world ...

I have never seen such an ugly animal
or one that is more useless."

(Laughter)

Tell us what you really think, Valdés.

(Laughter)

I'd like to have a word
about Valdés's drawing skills.

(Laughter)

I mean, what is that?

(Laughter)

I've never seen an illustration
of a sloth that's more useless.

(Laughter)

But I mean, on the plus side,

he has given the sloth
a remarkably humanlike face,

and sloths do have remarkably
humanlike faces.

This sloth I photographed in Costa Rica,
I think looks a lot like Ringo Starr.

(Laughter)

But then, sloths do bear an uncanny
resemblance to the The Beatles.

(Laughter)

Particularly pleased
with Paul, actually, on there.

But like The Beatles,
sloths are also extremely successful.

They come from an ancient line of mammals,
and there were once dozens of species

including the giant ground sloth,
which was the size of a small elephant

and one of the only animals big enough
to eat avocado pits whole

and disperse them.

So ...
(Laughter)

Some of you have worked it out already.

(Laughter)

That means that without sloths,

there might be no avocado on toast today,

leaving hipsters everywhere
totally bereft at breakfast.

(Laughter)

(Applause)

Today, there are six surviving species,
and they fall into two groups.

You've got your Bradypus
three-toed sloths,

they're the ones with the Beatles haircuts
and the Mona Lisa smiles.

Then, there are the two-toed sloths.

They look a little bit more like a cross
between a Wookiee and a pig.

They live in the jungles
of Central and South America,

and they're extremely prolific.

There was a survey
that was done in the 1970s

in a Panamanian tropical forest

that found that sloths were the most
numerically abundant large animal.

They took up one quarter
of the mammalian biomass.

Now, that's an awful lot of sloths

and suggests they're doing
something very right indeed.

So what if, rather than deriding
the sloth for being different,

we tried to learn from it instead?

We humans are obsessed with speed.

Busyness is a badge of honor,

and convenience trumps quality
in our quest for quick.

Our addiction to the express life
is choking us and the planet.

We idolize animals like the cheetah,
the "Ferrari of the animal kingdom,"

capable of doing naught to 60
in three seconds flat.

Well, so what?

(Laughter)

(Applause)

So what?

The sloth, on the other hand,

can reach a leisurely 17 feet a minute

with the wind behind it.

(Laughter)

But being fast is costly.

The cheetah is speedy,
but at the expense of strength.

They can't risk getting in a fight,

so they lose one in nine kills
to tougher predators like hyenas.

No wonder they're laughing.

(Laughter)

The sloth, on the other hand,

has taken a more stealthy
approach to dinner.

They survive by capturing and consuming

static leaves.

(Laughter)

But you see, leaves don't want
to be eaten any more than antelope do,

so they're loaded full of toxins
and very hard to digest.

So in order to consume them,

the sloth has also
had to become an athlete --

a digesting athlete.

(Laughter)

The sloth's secret weapon
is a four-chambered stomach

and plenty of time.

They have the slowest
digestion rate of any mammal.

And it can take up to a month
to process a single leaf,

which gives their liver plenty of time
to process those toxins.

So, sloths aren't lazy.

No, they're busy.

Digesting.

(Laughter)

Yeah, really busy.

(Laughter)

Hard at work, that sloth,
very hard at work.

And of course, leaves
have little calorific value,

so sloths have evolved to spend
as little energy as possible.

They do about 10 percent of the work
of a similar-sized mammal

and survive on as little
as 100 calories a day,

thanks to some ingenious adaptations.

The Bradypus, three-toed sloths,

they've got more neck bones
than any other mammal,

even a giraffe.

Which means they can turn their head
through 270 degrees

and graze all around them,

without having to actually bother
with the effort of moving their body.

(Laughter)

It also means that they are
surprisingly good swimmers.

Sloths can bob along in water

three times faster
than they can move on land,

kept afloat by ...

trapped wind.

(Laughter)

So --

(Laughter)

sloths are the only mammal that we know of
that don't do flatulence.

When they need to expel gas,

it's actually reabsorbed
into their bloodstream

and expelled orally
as a sort of mouth fart.

(Laughter)

Turning their lives upside down
saves further energy.

They have about half the skeletal muscle
of a terrestrial mammal.

They don't really have so many
of the extensor muscles

that are the weight-bearing muscles;

instead, they rely on retractor muscles
to pull themselves along.

They have long, hooked claws
and a high fatigue resistance,

so they can literally hook on and hang
like a happy, hairy hammock

for hours on end.

And sloths can do almost anything
in this inverted position.

They sleep, eat and even give birth.

Their throat and blood vessels
are uniquely adapted

to pump blood and to swallow food
against the force of gravity.

They have sticky bits on their ribs

that prevent their enormous stomach
from crushing their lungs.

And their fur grows
the opposite direction,

so they can drip dry
after a tropical drenching.

The only problem is,
if you turn a sloth the other way up,

gravity removes its dignity.

Audience: Awww.

They can't hold themselves upright.

And so they drag their bodies along
as if mountaineering on a flat surface.

And I think this is why
the early explorers like Valdés

thought so poorly of them,

because they were observing sloths
the wrong way up and out of context.

I've spent many happy hours
mesmerized by moving sloths.

Their lack of muscle hasn't impeded
their strength or agility.

Nature's zen masters of mellow
move like "Swan Lake" in slow mo --

(Laughter)

with the core control of a tai chi master.

This one has fallen asleep mid-move,
which is not uncommon.

(Laughter)

But you're probably wondering:

How does a dangling bag
of digesting leaves avoid being eaten?

Good question.

Well, this is one
of the sloth's main predators.

It's the harpy eagle.

It can fly at speeds
of up to 50 miles per hour,

has talons the size of a grizzly bear's,

razor-sharp eyesight,

and that ring of feathers focuses sound

so that it can hear
the slightest leaf rustle.

The sloth, on the other hand,
has poor hearing, bad eyesight,

and running from danger
is clearly not an option.

No, they survive by wearing
an invisibility cloak

worthy of Harry Potter.

Their fur has grooves
that attract moisture

and act as tiny hydroponic
gardens for algae,

and they also attract
a host of invertebrates.

So they are their own slow-moving,
miniature ecosystem.

They become one with the trees.

And we think that
their movements are so slow,

they slip under the radar
of the monstrous harpy

as it's flying about the canopy,
scanning for action.

Sloths are stealth ninjas,

and they rarely leave
the safety of the canopy --

except to defecate,

which they do about once a week
at the base of a tree.

Now, this risky and energetic behavior
has long been a mystery,

and there are lots of theories
as to why they do it.

But I think they're leaving surreptitious
scented messages for potential mates.

Because, you see, sloths are generally
silent, solitary creatures,

except for when the female is in heat.

She will climb to the top of a tree
and scream for sex.

In D-sharp.

(Laughter)

Don't believe me?

(Sound of sloth scream)

D-sharp.

This and only this note
will get the male's attention.

It mimics the sound
of the kiskadee flycatcher.

So the female remains covert,

even when yodeling for sex
at the top of her lungs.

Her clandestine booty calls
will carry for miles across the canopy,

and males will beat
a slow path towards her.

(Laughter)

I think scented messages in her dung
will help send Romeo up the right tree

so that he doesn't waste precious energy
scaling the wrong one.

Sex, by the way, is the only thing
that sloths do swiftly.

I've seen them do it in the wild,

and it's over and done
with in a matter of seconds.

But then, why waste precious energy on it,

particularly after that journey?

(Laughter)

Unlike other mammals,

sloths don't also waste time maintaining
a constant warm body temperature.

Energy from the sun is free,

so they bask in the sun like lizards

and wear an unusually thick coat
for the tropics to keep that heat in.

Sloths have a freakishly low metabolism.

And we think that this might be
one of the reasons

that they can sometimes
recover from injuries

that would kill most animals.

This sloth recovered
from a double amputation,

and I've known sloths
that have managed to survive

even power line electrocutions.

And we now think that a low metabolism
may well be key to surviving extinction.

Researchers at Kansas University
who were studying mollusks

found that a high metabolism
predicted which species of mollusk

had gone extinct.

Sloths have been around on this planet
in one shape or another

for over 40 million years.

The secret to their success
is their slothful nature.

They are energy-saving icons.

And I founded the Sloth
Appreciation Society

to both promote and protect
their slow, steady, sustainable lives.

I'm a pretty speedy character.

I'm sure you've guessed.

And the sloths have taught me
a lot about slowing down.

And I think that the planet would benefit

if we all took a slowly digested
leaf out of their book.

How about we all embrace our inner sloth

by slowing down,

being more mindful,

reducing wasteful convenience,

being economical with our energy,

recycling creatively

and reconnecting with nature.

Otherwise, I fear,

it will be us humans that turn out to be

"the stupidest animals
that can be found in the world."

Thank you very much.

May the sloth be with you!

(Applause)