Natural Curiosities (2013–…): Season 4, Episode 4 - Curious Counters - full transcript

The natural world is full
of extraordinary animals

with amazing life histories.

Yet, certain stories
are more intriguing than others'.

The mysteries
of a butterfly's life cycle,

or the strange biology
of the emperor penguin.

Some of these creatures were
surrounded by fantastic

myths and misunderstandings.

Others have only recently
revealed their secrets.

These are the creatures
that stand out from the crowd.

The curiosities that I find
particularly fascinating.

At the turn of the 19th century,



a German horse called Hans
hit the headlines.

It was claimed that he could perform

complicated mathematical
calculations.

And Chinese records
tell of a species of bamboo

that seems able to count the years,

for all individual plants growing
in different parts of the world

flower at exactly the same time.

Can a horse and a plant truly count?

In 1891, a retired German
mathematics teacher

called Wilhelm von Osten
decided to do a very unusual thing.

He began to teach maths
to his horse, Hans.

After four years,
Hans was presented to the public

to demonstrate
his remarkable abilities.

To everyone's amazement,



he was able to count the number
of people in the audience,

perform complex arithmetic,
read a clock,

recognise
and identify playing cards,

and he knew the calendar
of the whole year.

To signal the correct answer,
Hans tapped his hoof.

He was accurate and consistent,

and was declared worldwide
as the first horse genius.

It all seemed incredible.

Could Hans the horse really count?

And why might animals
need to do so anyway?

Well, it could help them keep track
of the number within a group.

They might need to know
how many offspring they have.

And, for many animals,
it's an advantage to know

if one quantity is smaller or
larger than another.

ROARING SOUNDS

Studies of lions in the Serengeti

suggest that they're able
to count roars

in order to assess
the size of a competing pride.

They estimate the number of
challengers from the sound

of the incoming roars, and compare
this to the size of their own pride.

They will only decide to defend
themselves if their pride is larger.

But it seems their counting
is limited

to no more than five or six roars.

Could Hans the horse
be drawing on his wild instincts

to use numbers in this way?

Wild horses live in small bands

that can join up to form big herds
of more than 100 animals.

They have a dominant stallion,
and a firm pecking order.

Horses are not territorial,

and have no great need to know
the exact numbers in their own herd.

Or another.

But they do sometimes
make judgments about quantity

when choosing food.

This basic ability to judge
differences in amounts

is the first step
in the skill of counting.

But what methods might animals use
to assess numbers?

There are several ways
to keep count.

We can count precisely
to very high numbers,

and have created number symbols
that indicate exact amounts.

So, we know that the number five,
for example, indicates five objects.

Even if we can't see them.

Perhaps animals judge quantity
in a similar way,

and have their own pictorial
shapes perhaps, in mind,

that match an amount.

Another idea is that animals judge
differences in amount

as an accumulation,

just like filling
a measuring tube with a liquid.

Alternatively,
the mind may have memory slots

that store a limited number
of objects

in the same way as a filing cabinet
stores cards.

So, there could be several different
ways in which animals

judge quantity or amounts.

Hans the horse appeared to count
very precisely to high numbers.

This seems an improbable feat
for any animal.

But, recently, an extraordinary
discovery showed that an insect

with a brain a fraction
of the size of a horse's,

can count with great accuracy.

The ant.

Ants are social animals
that use scent trails

and visual reference points
to find their way around.

But, in the desert,
where scent evaporates,

and the landscape is featureless,

they nonetheless seem able
to navigate successfully.

In 2007, researchers investigated
how Tunisian desert ants

find their way home from
foraging trips across barren plains.

It's known that ants can measure
and integrate two parameters -

direction, and distance of travel.

The desert sun helps an ant
orientate its direction.

But how do they measure distance?

Experiments were performed to
manipulate the ant's stride length

to see if they were counting the
number of footsteps that they took.

Based on a featureless environment,

ants learned to travel home
to a set point.

Then, stilt-like extensions
were glued to their legs

to lengthen their stride.

These ants took
the right number of steps,

but, because
of the increased leg length,

they marched right past their goal.

So, ants are able to log the number
of steps that they take,

perhaps not counting them
in the way that we do,

but they do have
an internal counter.

Unlike ants, horses have no need
to count their steps,

so it's unlikely that they have
an internal pedometer.

But they can, nonetheless,
assess quantity.

Wild horses are highly social.

And, if one is harassed by flies,

it will seek to join the largest
available group for protection.

So, horses can estimate numbers and
recognise differences in size.

But this is a much simpler ability

than the counting that
Hans the horse was doing.

There seem to be no limit to
the complexity of the calculations

that Hans could compute,
and his answers were precise.

For many, this seemed
too extraordinary to be true.

In 1904, the German Board
of Education was so intrigued

that they formed
a 13-strong commission

to look closely at how Hans could
perform such amazing feats.

They wondered if Hans' owner
was using trickery

to feed him the answers.

To test this,

other members of the board were
given questions and answers

to pose to Hans.

Incredibly,
Hans still answered correctly.

Eminent psychologist Oskar Pfungst

then came to investigate
Hans' skills further.

And confirmed that he appeared
to understand numerology,

and the abstract idea of counting
words associated with numbers.

For Hans to perform
complex mathematics,

he would need to understand

much more than just differences
in quantities.

He would need to recognise
the fact that two

is smaller than six.

And that specific number symbols

always go with
the corresponding amounts.

To count, he would also need
to realise that numbers occur

in a set, repeatable sequence.

And that the last number counted

represents the total
of the whole set.

In effect, that he'd answered the
question, "How many do you have?"

It seems that many animals
have a sense of number,

but few are conscious
of an exact total.

For most animals, the ability
to recognise an amount,

and to compare it to others,
is all they need.

Usually, a crude estimate,
between more or less,

or larger and smaller, is enough.

But could horses be an exception?

Could they have advanced
counting skills?

In 2009, experiments showed

that horses could count
to a certain level.

I'm going to take false apples,

ones that don't have a smell
which might confuse the issue,

and show the horse one...

..two...

..three...

..four in here.

And one, two...

..in there.

Now, then, which do you want?

Thank you.

Yes.

Four.

Repeated tests of 14 horses

found that they consistently
selected buckets

that contained
a higher number of apples.

But that sense of number
was limited -

they could only keep track
of numbers up to about six,

and no higher.

So, it seemed incredible

that Hans the horse had
such advanced counting skills.

Perhaps he was being helped
or trained in some way by his owner?

There is little doubt that most
horses are very intelligent animals.

And, if they're given clear signals,

they can indeed learn
to perform complicated routines.

Hans the horse
was schooled for many years,

so, perhaps, he had developed an
advanced understanding of numbers

when given clear instructions
by his owner.

In the wild,

horses communicate with each other
by using quite a rich body language.

Wild Mustang use a complex silent
one that scientists call Equus.

It consists of a series of gestures,

that are much like signing
for the deaf.

Every part of the horse
conveys meaning.

Especially the ears, tongues,
lips, shoulders, and necks.

They have the sensitivity
and intelligence

to interpret the tiniest of
gestures, even breathing patterns.

And, from this, they can judge
each other's intentions.

And it's this ability
to sense subtle changes

in physical and emotional
states of those around them,

that has made horses
so responsive to training.

So, did Hans the horse
really understand numbers,

or was something fishy going on?

In 1907, after further research,

Professor Oskar Pfungst discovered

that Hans could
only get the correct answer

if the questioner knew the answer,

and then,
only if he could see his face.

That was a significant discovery.

I have my own clever horse,
her name is Millie.

Millie, what is two plus two?

HORSE SCRAPES HOOF FOUR TIMES

There you are.

All right, let me ask you something
more difficult, Millie.

Millie, what is eight plus two
minus seven?

HORSE SCRAPES HOOF THREE TIMES

Yes! Well done, Millie!

There you are.

Millie is, indeed, a clever horse,

and appears to be able
to do arithmetic.

That's because, in fact, she can
react to very subtle signals.

If I take my hand off her
and step forward...

..she paws.

And, if I step back, she stops.

So, eventually, it was shown that
Hans was not a mathematician genius,

he was just extremely skilled
at following body language.

Particularly those facial signals
that questioners might give

when they reach the right answer
to the question.

Some animals can, of course, count.

Ants can.

But, for most animals, knowing the
difference between more or less

is all they need for survival.

Hans the horse baffled
all the experts for many years.

But true counting is, in fact,
a complex concept

that few animals grasp.

There is a plant, however,

that may be able to do so
in a surprising way.

It's the fastest-growing plant
on earth.

A type of grass we know as bamboo.

Remarkably, some species only flower
every 30 or 60 years.

Others do so in cycles
of over 100 years.

But how do these plants
measure time?

Can they count down the years?

Flowers that bloom in the spring,
like these,

are triggered to do so
by a rise in temperature

and an increase
in the length of the days.

But bamboos flower on an
entirely different system.

They don't do so annually,

but at intervals which far
exceed the length of a human life.

The function of flowers
is to reproduce.

Bright, sweet-smelling blooms
attract insects,

which carry pollen from one plant
to another, and so fertilise them.

The flowers of bamboos
are unassuming and drab.

Because they're pollinated not
by insects, but by the wind.

Most grasses, indeed,
have flowers that are so small

that they tend to go unnoticed.

Since their pollen
is carried by the wind,

they have no need
for spectacular blooms.

Bamboos are the largest
members of the grass family,

and they were introduced to Britain
from Asia during the 1800s.

Many were planted here in Kew.

But, for over 100 years,
nobody ever saw them flower.

Bamboos grow in tropical
or subtropical climates.

They are, in fact,
one of the most widespread plants.

But, despite this,
few people ever see them flower.

The reason is,
they only do so very rarely.

We know this because
early collectors and scholars

have kept careful records that, in
some cases, extend over centuries.

Some are still preserved
at Kew Gardens in London,

which houses one of the largest
historical collections of plants

in the world.

This is a specimen
of the giant timber bamboo.

Phyllostachys bambusoides.

It was collected, as this
label shows, in China in 1855.

At the time,
bamboo was clearly in flower.

There they are.

Quite small and obscure.

Much like those of other grasses.

And then, in the 1960s,

Phyllostachys bambusoides
bloomed again.

And here is the evidence.

This specimen is from 1961.

These are just the records
from European collectors.

Chinese and Japanese accounts go
back much further, over 1,000 years.

Together, these records show that
Phyllostachys bambusoides

flowers in cycles
of around 110 years.

And there was another surprise.

Phyllostachys
is native to China and Japan.

But, in the 19th century,

it was introduced to other countries
as an ornamental garden plant.

And when it flowered,
most recently in the 1960s,

it came into bloom
not just in its native Asia,

but all around the world
at the same time.

It's a most bizarre life cycle.

How do bamboos flower
at the same time

when separated
by thousands of miles?

The unusually long flowering cycle
of bamboo was well-known in China.

But there were other stories
about its flowering

that were picked up by European
visitors trading in the Orient.

Bamboo was valued by local people
for its sturdiness and durability.

The bamboo was held in such respect

that it featured prominently
in the paintings and calligraphy

of ancient Chinese and Japanese
artists.

Although the bamboo is deeply
rooted in local cultures,

one part of the plant has instilled
fear since the earliest times.

An old Chinese proverb says
when the bamboo flowers,

it means either
pestilence or famine.

In 1898, a medical officer
called John Mitford Atkinson,

based at a government
hospital in Hong Kong,

sent some bamboo seeds to the keeper
of the horarium here at Kew.

And, with it, this letter.

In it, he writes that,

"Oddly enough, in the years
that the bamboo flowered,

"plague epidemics seemed always
to ravage the colony."

So, could there perhaps be some
truth in these old sayings?

So, here was another mystery.

Not only does the bamboo flower
very rarely, but when it does,

it seemingly
causes death and famine.

The bamboo's life cycle
is truly puzzling.

How can a plant survive by only
flowering every 100 years?

The answer, it seems,
can be found underground.

This is the rhizome of a bamboo.

It extends in all directions
from the plant.

Putting down roots,
and sending up shoots.

It's a very efficient way
of spreading.

As gardeners know to their cost,

because you plant
one patch of bamboo,

and before you know where you are,
it's taken over the entire garden.

It's a way of spreading
that has its advantages.

Bamboos don't have to flower
and seed every year.

Instead, they grow a whole network
of underground rhizomes,

and put their energy straight
into producing fast-growing

and strong shoots.

The stems emerge from the ground
at their full width,

and shoot to the sky
like a periscope.

In just a few weeks,
they reach their full height.

After this, they don't get
any taller or thicker.

They simply expand outwards,
like a family or colony.

This is a giant bamboo.

Some species can reach the
extraordinary height of 30 metres,

and, to achieve that
in a single season,

they have to grow at the
phenomenal rate of a metre a day.

You can literally see them grow.

But, when it comes to flowering,

bamboos are one of the slowest.

What could be the reason
for this long interval?

In Southeast Asia, there are trees
that may give us a clue.

They're called dipterocarps
and, like bamboos,

they also flower and seed
synchronously,

but on a shorter timescale.

They produce seeds en masse
every two to seven years.

And when they do,
they swamp the forest floor

with an abundant supply of food.

This attracts small mammals
from all around.

By fruiting at the same time,
the trees ensure that,

despite the many predators,
some of the seeds will survive,

and grow into new seedlings.

Bamboo seeds
are also highly nutritious,

and lots of animals
like to feed on them.

Rats, mice, birds, monkeys,
even elephants.

They all devour huge numbers
of the seeds, given the chance.

So, bamboos may fare better

if they synchronise their
reproduction to flower and seed

at the same time.

By overwhelming
their enemies with food,

they can ensure that at least
some of their seeds will survive.

Once bamboos
fell into this flowering cycle,

any that flowered too early would
lose all their seeds to predators.

In years when bamboos do flower,

there is often a boom
in rodent populations.

But once the small mammals
have stripped the forest of seeds,

they swarm into fields and villages
to devour people's crops and grain.

The rats carry dangerous diseases,

and the result is often death
and starvation among people.

So, paradoxically, the bamboo,

which provides an essential
livelihood for so many people,

at times causes
death and devastation.

When Atkinson made a connection
between bamboo flowering

and plague epidemics in Hong Kong
during the 19th century,

he had little idea of the
true reasons behind this.

But, as it turns out, he was right.

And the old Chinese proverb
contained a deadly prophecy.

While the reason
behind the synchronous flowering

may have been explained,

it's still a mystery as to
how bamboos actually do it.

Could the plants
be counting down the years

in order to all flower
at the same time?

It seems the answer may,
once again, lie within their roots.

The bamboo's unusual way
of reproducing

via a network
of underground rhizomes

means that most plants
are, ultimately, from the
same mother plant.

These clumps have been shared
across the world,

and although they're now
in different locations,

they still carry
the same genetic make-up.

They are effectively clones
of the parent plant.

And it may be that they have some
kind of internal memory

that is also passed on.

Scientists believe that the bamboo's
roots contain some kind of clock

that enables them to
count the passing of the years.

How they do that is still a mystery.

But, nonetheless, there is an
animal that might give us a clue.

Periodical cicadas in North America
spend 17 years underground,

feeding on the sap from tree roots.

Within the space of a few days,

the whole population
emerges in their millions.

Their mission is to breed.

But what triggers the cicadas to
all emerge at exactly the same time

every 17 years?

We know that,
when feeding underground,

they can detect changes
in the tree sap each spring,

and so tell the passing of a year.

Could it be that bamboos
also count the years in this way?

It's possible that bamboos register
the passing of the seasons

in a similar way
by changes in their sap.

We just don't know.

But, while the exact mechanism
remains a mystery,

it may well prove that these
time-measuring plants, bamboos,

are the master mathematicians
of the non-human world.

True counting
is very rare in nature.

But some animals and plants
achieve numerical feats

that are astonishing
in their own right.