All language subtitles for David.Attenboroughs.Natural.Curiosities.Series.3.6of6.Remarkable.Regeneration.720p.HDTV.x264.AAC.MVGroup.org

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The natural world is
full of extraordinary

animals, with amazing
life histories.

Yet, certain stories are
more intriguing than most.

The mysteries of a
butterfly's life cycle,

or the strange biology
of the Emperor penguin.

Some of these creatures
were surrounded by myth

and misunderstandings,
for a very long time.

And some, have only recently
revealed their secrets.

These are the animals, that
stand out from the crowd,

The curiosities, I find
particularly fascinating.

Salamanders can regenerate
entire legs and tails,

to replace ones that they loose.

And moose, can regrow their
enormous antlers every year.

How do these animals
regenerate entire body parts?

And why isn't it possible, for
all animals, to do the same?

When I was a boy,
my father gave me

one of these, for
my 8th birthday.

It's a fire salamander.

They may look like lizards, but
in fact they're not reptiles.

They're amphibians,
with moist skins.

For centuries, mythical stories
surrounded these creatures.

It was believed, that they
were icy cold animals,

and could dwell within
fires, unharmed by the heat.

Although their fire surviving
powers may be untrue,

the salamander, nonetheless,
possesses a real natural ability,

that is just as extraordinary.

They're able to regrow, damaged tails,
legs, and other parts of the body,

through a process
called, regeneration.

There are more than 600 different
species of salamander.

They range in size, from just
a couple of centimeters,

up to the world's
largest amphibian,

The Chinese giant salamander,

that can grow to over a
meter and a half in length.

Salamanders are
predators, and many hunt

for small invertebrates,
such as slugs and worms.

But sometimes, they
hunt each other.

with dramatic consequences.

This tiny, North American
red back salamander

is on the menu of the, much
bigger, seal salamander.

Time to make a retreat.

This may look shocking, but the
red back isn't badly injured.

A weak point in its skin, allows
its tail, to break off easily.

Incredibly, it will regrow a new
tail, in just a matter of weeks.

This ability, to replace
an entire body part,

is unusual among
adult vertebrates,

and seems almost magical.

Regeneration is a subject,
that fascinates us.

Modern medicine has spent
a lot of money and time,

studying the ways, our own
bodies can regenerate tissue.

All living creatures, including
humans, have the ability

to repair damaged
parts of the body,

but the extend of that
repair, varies considerably.

As small infants, we have
the ability to regrow

the tips of our fingers
if they're severed,

but we loose this
ability, as we age.

So, animals, like salamanders,

with their super
regenerative powers,

seem intriguing to us.

Regeneration had been known
about, since ancient times.

But for a long time, no one
understood, how it happened.

In the 17th and 18th century,

there was a new wave of
scientific discovery.

A brilliant Italian scientist,
named Lazzaro Spallanzani,

made meticulous
observations into

regeneration, across
many different species.

And shared his ideas,
in detailed letters.

In November 1765, he wrote
to the eminent scientist

Charles Bonnet, whom he
regularly corresponded with,

to announce, that
he had discovered

tail regeneration
in salamanders.

Throughout the following
year, he followed up his

initial observations, with
numerous experiments,

to try to understand,
how the salamander

could regrow a tail,
just like the original.

He found, that all species
of salamander he tested,

could regrow their
tails, when injured,

and they did so, more rapidly
in summer, than in winter,

and retain this incredible
ability throughout their lives.

Spallanzani advocated
a radical theory.

He thought, that salamanders
already possessed a number

of miniature spare parts,
at the base of each limb,

that could grow in size, to
replace a lost or damaged one.

He was unable to prove this,
but he didn't give up.

He studied salamander
tadpoles, and came up

with another, even
more interesting idea.

A year after his initial
letter, Spallanzani

once again wrote
to Charles Bonnet.

This time with detailed
descriptions of

further experiments
into tail regeneration.

Most notably, in this
description, he wrote:

I am almost lead to believe,
that the tail regenerates,

in tadpoles, are more of an
elongation of the old parts,

than a development from a germ.

This suggests, that Spallanzani
was on the right track.

But the idea, that the salamander
could regrow a new tail,

from seemingly nothing,
was not well supported.

And Spallanzani was
therefore never

willing to pursue
the idea further.

However, there's
no doubt, that his

research helped to
lead other scientists

closer towards proving
what really happens,

when a salamander
regrows its tail.

In fact, Spallanzani's rough
sketches did make sense.

For they were the first to describe,
some of the vital processes,

in the remarkable growth of new limbs,
that we understand better today.

When a limb is lost, the
exposed blood vessels

and tissue, contract, to
quickly stop any bleeding.

Then, skin from the edges,
begins to grow across the

damaged area, to protect
the body from infection.

Now, cells that
were once dormant,

begin dividing and multiplying,
to create new ones.

Each cell retains
a kind of memory,

of the type of tissue
it used to be,

So, a new cell that regrows
from damaged muscle,

will always become muscle.

Within weeks, the salamander
has a full-grown leg,

almost identical
to the original.

Although we now know the
steps, that take place

during the regeneration
of body parts,

we still don't fully understand,

what triggers this
kind of response.

But it seems, the answer may lie

in how the salamander's
body responds to injury.

In humans, if an arm is severed,

the cells die, alerting the
immune system to the problem.

In response, the area becomes
swollen, and is covered over

with scar tissue, preventing
any new growth occurring.

But in salamanders, the immune
system responds differently.

And instead of forming a scar,
it triggers regeneration.

Another, rather unusual
looking salamander,

that lives in the fresh
waters of Mexico,

sheds new light, on
how this happens.

Axolotls are among the best
re-generators in the natural world.

And scientists wondered, if their
blood played a role, in the process.

Like us, they have special
white blood cells,

that consume invading
bacteria and

damaged tissue around
injuries and wounds.

Researchers removed them, and
the results were surprising.

The axolotl was unable,
to regrow new limbs.

So white blood cells,
were part of the

secret of their powers
of regeneration

Understanding the role
of the salamander's

blood cells in regrowing
limbs, could be a step

towards discovering why they
can regenerate body parts,

and we can't.

All amphibians have tadpoles,
which develop limbs

and enable them,
to move onto land.

But salamanders are able to
re-trigger that remarkable process.

We too, undergo extraordinary
development in the womb.

Maybe, like the salamander,
there is a way of us,

retaining this ability, into
our adult lives as well.

The salamander has a truly
amazing ability, to regrow

complex body parts, to enhance
its chances of survival.

While we don’t yet know all
the answers, it's likely,

that this incredible creature,
could revolutionize

modern medicine, and the
way we treat injuries.

Next, we uncover the
secret behind how the

moose regrows its enormous
new antlers every year.

and discover what happens,
when regeneration goes wrong.

The salamander's
ability to re-grow

entire limbs, is
truly remarkable.

But moose and other deer,
possess huge antlers,

that are shed and
re-grown, each season.

How can they regenerate such

large body parts,
every single year?

This impressive skeleton,
belongs to one of

the biggest deer, to
ever live on the planet.

It's an Irish Elk.

His antlers were enormous,
they're almost 4 meters,

12 feet across, and
they weigh 40 kilos.

An Irishman, named Dr. Molyneux,
first scientifically

described the elk, in 1697,

from specimens, taken out
of an Irish peat bog.

Some believed, that this
elk, was a large moose,

and were convinced,
living specimens could be

found elsewhere, across
Europe and Russia.

But not everyone agreed.

And the debate, about the
life of this creature,

would continue for
more than 100 years.

The skeleton of an Irish elk,

looked very similar,
to that of a moose.

So, it's easy to see, why many

believed them to be
the same animal.

Both have very
impressive antlers.

Antlers are only found in the deer
family, and are made of bone.

Unlike horns, which are
permanent structures,

they are shed and
replaced, every year.

But how can deer re-grow
huge chunks of bone?

Something, no other
mammal can do.

Moose, like this young
bull behind me,

start growing their new
antlers immediately

after they shed their old ones.

The antlers first
appear on little bumps,

on either side of the
head, known as pedicles.

And they have a soft furry
covering, called velvet.

This is vital to their amazing
powers of regeneration.

Blood vessels at the
base, start the growth.

But as the antler gets longer,
this blood supply is cut off.

Then, blood vessels within
the velvet take over,

and transport nutrients and growth
hormones to the growing tips.

In older males, the antlers can
grow at a rate of 2 cm a day,

making it the fastest
growing bone of any animal.

Once at full size,
the velvet is shed.

The animal rubs its
head against a tree,

to encourage the thin
velvet, to fall off.

It may look gruesome, but
it's a natural part of

the annual cycle, and
does the animal no harm.

But why should a
huge set of antlers

be regrown every year?

It's a question, that
baffled early naturalists.

Until Charles Darwin
suggested, it may be

to do with attracting
the opposite sex.

In the first few years of
adulthood, the antlers are small.

And as a result, young males remain
subordinate to the larger bulls.

But as they get older,
their body size increases,

so, the antlers
will also increase,

eventually becoming
impressive ornaments

with which to compete
for females.

Those with the biggest antlers,

are certainly more
attractive to the females.

Maybe, they are an indicator
of fitness and strength.

And it's no coincidence, that
antlers are at their full size,

during the breeding season.

This is a time, when
a bull must protect

his harem, and see
off competitors.

Competing males tilt
their heads, to show off

their antlers, to
their best advantage.

But if the bulls are
equally matched,

then, the competitors fight.

The winner, then gains
access to the females.

The benefits of such
a victory are huge.

But to get to that point,
every young bull must,

for many years, grow
and regrow antlers.

It's a big investment, draining
the body of vital resources.

And no investment was bigger,

than that, of the Irish Elk.

The sheer size of these
antlers, had let some to argue,

that they were unlikely to have
been used in physical combat.

Unlike other deer, the
antlers of the Irish elk,

grew with a large flat, palm-like
plane, facing forward.

So then, if a bull
looked straight ahead,

it would be at its biggest
and most impressive.

In this way, they may have
been able to intimidate

rivals and attract females,
without actually fighting.

So, although the
Irish elk was armed

with what appeared to
be enormous weapons,

it seems, they were
mostly for show.

Now, this strategy,
may have been

an advantage for the large elk.

Fighting is always
a risky business,

and will often result
in serious injuries.

After the breeding season,
the antlers are discarded.

Moose shed theirs in the winter,

whereas smaller deer, keep
theirs until the next spring.

This maybe, because the
moose antlers, are such

a heavy load to carry,
throughout the winter.

But why are antlers shed at all?

Antlers are made of dead
bone, and can't be repaired.

If a moose damages an
antler during a fight,

it will loose its chance of
mating, for that season.

By shedding and regrowing
their antlers each year,

bulls ensure, that they
stay in the mating game.

Just before antlers are shed,

minerals within them, are
reabsorbed from the base,

weakening the structure, so
that they eventually fall off.

The flesh underneath is
exposed, but not for long,

as new skin soon
covers the wound.

Experiments have
shown, that the skin

lesion that forms
over the open wound,

creates a connection with
the underlying tissue,

that is crucial to regeneration.

If this connection
isn't laid, the

production of velvet
will be interrupted,

and the antlers will
either not grow at all,

or develop into strange shapes.

So, what about the Irish elk?

Could the problems
of regenerating such

gigantic antlers, have
determined its faith?

The French scientist
Georges Cuvier,

was keen to demonstrate,
that the Irish elk

was a unique species,
that had become extinct.

To prove his point,
Cuvier undertook a

detailed examination
of Irish elk fossils.

He was able to show,
that it was indeed

a distinct type of deer, that
could no longer be found alive.

And so, the Irish elk,
was one of the first

animals we recognized,
as being extinct.

Georges Cuvier had solved the
question, of whether or not,

the Irish elk and moose, were
one and the same creature.

But why did the
Irish elk die out?

Cuvier suggested, that
evolution had set

it on a course of ever
increasing growth.

And that eventually, the
antlers became so large,

that the poor animal could
not even lift its neck.

He may not have been
that far from the truth.

It is now thought, that
the annual growth of the

Irish elk antlers, put a
strain on their bodies.

A significant proportion of
minerals, within their bones,

were extracted and moved
into their growing antlers.

This led to a seasonal
osteoporosis,

with their bones weakening.

They were, in effect, robbing

one part of their body,
to boost another.

It was a gamble, that worked
for thousands of years.

But around 10,000 years ago,
the climate began to warm.

The nutrient-rich
grasses, that the elk

relied upon, began to disappear.

Growing massive antlers,
may now have been too much

of a drain, and permanently
weakened the skeleton.

The change in diet,
may also have

effected their ability to breed,

with females no longer able
to produce young every year.

Whatever the reason, the Irish
elk, with its magnificent antlers,

finally vanished
from the landscape.

And in its place, the
moose has become

the largest deer
on earth, today.

So, while regeneration
can give the salamander

a second chance, to a full life,

the yearly regeneration
of antlers

in male moose, is
a risky strategy.

But one, with huge rewards

for those with the best antlers.