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65 million years ago,
an environmental catastrophe
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wiped out the dinosaurs and over half
of all other species then living on the planet.
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00:00:16,006 --> 00:00:20,841
There is now strong evidence that
similar losses are about to happen again.
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This is Hawaii.
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It's the most isolated group
of islands on the planet,
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2,400 miles away from the Californian coast.
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From the air, it may look like an island paradise,
but the history of its animals and plants,
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since humanity first reached it 1,700 years ago,
is very alarming.
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It can be seen as an example in miniature
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00:01:27,926 --> 00:01:32,158
of what mankind has done
to the planet as a whole.
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In environmental terms,
it is tragically impoverished.
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Small islands are especially vulnerable
to the environmental changes
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that so often follow the arrival of humans.
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Hawaii, not so long ago, had more
unique kinds of plants and animals
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than any other group of islands on earth.
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But this lush beauty is deceptive.
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These mountain slopes, forests and lowlands,
which once teemed with such unique species,
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have today been emptied
of their biological riches.
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The islands give us all a dramatic warning
of the level of losses
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that could soon occur right across the planet.
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Hundreds of species of both
animals and plants have disappeared
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since humanity first came to Hawaii.
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It's absolutely clear from research,
both here on Hawaii and on other islands,
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that whenever human beings settle on an island,
great loss of species occurs.
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If we are to control
our impact on the environment,
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it's absolutely essential that we understand
just why this should be.
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Across the world, from the tropics to the icecaps,
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we are surrounded
by an extraordinary variety of life.
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We have so far
named one and a half million different species.
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There could be as many as a hundred million.
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This great abundance of life
is known as biodiversity.
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It's this richness that today is threatened
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as our species attempts
to fulfil its biological needs.
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In this programme, we will identify
the five human activities
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that are causing such destruction
that they lead some experts to foresee
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a mass extinction of other species
during this present century.
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To begin with, it may help to get an idea
of the scale of environmental change
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necessary to cause
a global mass extinction of life.
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To do this, we can look back 65 million years
to the last great wave of extinctions
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that left the dinosaurs as nothing more
than fossils for us to study and display.
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Many scientists believe that this event was
largely due to the environmental after effects
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of the collision with the earth
of a ten-mile wide meteor
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travelling at 25,000 miles an hour.
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This was the equivalent
to the simultaneous detonation
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00:04:17,166 --> 00:04:22,160
of 10,000 times the world's
total arsenal of nuclear warheads.
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00:04:22,926 --> 00:04:27,397
Superheated fragments of rock
set half the world's plants on fire.
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00:04:28,686 --> 00:04:32,361
Dense clouds of dust
blocked out the sun for months on end,
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sending temperatures plummeting in what
had previously been a largely tropical world.
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The rain that fell was acid and poisonous.
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The cumulative result of all that
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was the extinction of over 50%
of all species on the planet.
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00:04:52,446 --> 00:04:55,438
There's a place in Arizona where a meteor,
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only a tiny fraction of the size of the one thought
to have led to the disappearance of the dinosaurs,
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has left its mark.
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On a global scale, it's a mere pinprick,
but that mark is enormously impressive.
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00:05:17,966 --> 00:05:21,879
Many are now suggesting
that the impact of our own species
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may represent for the rest of life on earth
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the biological equivalent
of a modern meteor strike.
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00:05:32,406 --> 00:05:38,356
It may seem somewhat fanciful to compare
the effect humanity is having on biodiversity
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00:05:38,646 --> 00:05:43,436
with the worldwide catastrophe
caused by a massive meteor impact.
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But there's a lot of evidence to show that we
are on the very brink of an extinction event.
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So the comparison is not without relevance.
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If we want to see what humanity
has done to its environment,
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a very good place to start is where
humanity itself started, in Africa.
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(MELODIC AFRICAN SINGING)
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Here, on the savannahs, we can still see
great herds of what scientists call
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mega fauna, the big mammals.
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Why is it, if you want to see big herds
of large mammals, you have to come to Africa?
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The answer's pretty obvious -
it's the only place where there are such things.
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If you went anywhere else,
you'd be in for a big disappointment.
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But it wasn't always that way.
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50,000 years ago,
there were big herds of big animals
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on every continent on the planet
except Antarctica.
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Then, around that time, in a very short period,
those animals began to go extinct.
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At the same time,
human beings were beginning to expand
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00:07:16,686 --> 00:07:20,565
from the continent where they began,
in Africa, right across the planet.
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Was that a coincidence?
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0r was it the first evidence
that human beings could have an effect
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on the rest of the animals on earth,
unlike that of any other species?
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00:07:32,726 --> 00:07:37,436
In North America, two thirds
of all big mammal species were lost.
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00:07:37,526 --> 00:07:40,165
What was it like there before that happened?
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00:07:40,406 --> 00:07:43,921
Biologist Jared Diamond
has made a detailed survey
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00:07:43,766 --> 00:07:46,724
of the mega fauna extinctions worldwide.
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Here around us in Los Angeles,
the mega fauna that went extinct
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00:07:51,206 --> 00:07:55,836
consisted largely of mammals;
there were camels, we had a lion here.
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00:07:56,126 --> 00:07:59,323
If we could have been standing here
14,000 years ago,
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00:07:59,486 --> 00:08:03,798
it would have looked like the Serengeti Plains,
with lions and cheetahs and elephants.
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(ATTENBOROUGH) Could the hunting of big
mammals by those ancestral humans
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really have played a role in their disappearance?
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(DIAMOND) The one correlation around the world
is that the mega faunal extinctions happened
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whenever humans arrived in the area -
arriving in Australia 40,000 years ago,
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00:08:21,526 --> 00:08:25,883
in the Americas 13,000 years ago,
in New Zealand, 1,000 years ago -
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that, I think, is enough to convict humans.
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00:08:30,486 --> 00:08:34,479
There are still a few kinds
of big mammals left in North America,
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such as these carefully protected bison
on the plains of South Dakota.
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These are big animals
and potentially very dangerous,
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which is why I must stay in a car
if I approach them as closely as this.
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These are small compared with some of
the huge animals that once roamed these plains.
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There was the mammoth,
the size of the African elephant,
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00:09:00,046 --> 00:09:04,562
sabre-toothed cats,
a ground sloth weighing three tons,
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a beaver the size of a bear.
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And that raises the question
of how human beings, on foot,
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armed with nothing more
than bows and arrows and spears,
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could hunt such monsters so successfully
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that they contributed significantly
to their extinction.
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Surprisingly, the answer
is to be found back in Africa -
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by investigating why big animals
did not die out here,
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despite this being the very place where
humans first developed their hunting skills.
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The big animals of Africa had been evolving
along with humans for five million years.
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As humans started out as ineffective hunters,
then gradually evolved to be effective hunters,
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so the big animals of Africa had a long time
to learn fear of humans.
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Unfortunately for the big animals
around us here in Los Angeles,
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the first humans they saw were the best
professional game-hunters in human history.
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(ATTENBOROUGH)
None of those big mammals outside Africa
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had ever seen human beings before
and didn't recognise them as predators.
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So instead of being fierce,
they probably appeared almost tame.
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As a consequence, they were easy to hunt.
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But that was not all.
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Human beings are what biologists call
switching predators.
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John Lawton is an expert in the study
of animal populations.
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A switching predator is a predator
with a variety of prey available to it,
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able to attack a wide range of prey items,
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so if any one prey gets rare, it can switch
to an alternative kind of prey.
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That way he can work his way
through a smorgasbord of prey items,
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sustaining its population on whatever happens
to be common at the time.
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To get an idea of how a switching predator
like those early humans
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can have such a damaging affect
on other species, we can look at a modern story
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involving another and rather surprising
switching predator from Europe.
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In the mid-1970s, five hedgehogs
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were taken from the Scottish mainland,
where they're common,
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and released as garden pets
on the island of South Uist, off the west coast.
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It's an island too remote for the hedgehog
ever to have reached by itself.
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They and their descendants
took to living in old rabbit burrows.
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The island turned out to be a virtually
perfect place for hedgehogs,
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with no predators to control their numbers.
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Being a switching predator, the hedgehog will
feed on anything of the right size it can find.
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Slugs, snails and worms are among its favourites
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and they're hugely abundant
in the damp climate here.
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So well did the island suit the hedgehog
that those original five
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have given rise to a population today
of around 10,000 hedgehogs.
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Originally, other animals also benefited
from the lack of predators.
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The dunlin had always nested here successfully,
for although it lays its eggs on the ground,
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there was nothing here to take them...
but the hedgehog changed all that.
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In the way of a switching predator,
it's always looking for new kinds of food.
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It turns out that hedgehogs will happily switch
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from feeding on slugs and worms to dunlin eggs.
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This switch led to a drastic collapse
in the dunlin's breeding success.
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Unfortunately, the story doesn't end there.
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At low tide, South Uist is connected
to other islands by sandbars.
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The hedgehogs can simply walk
from one island to another,
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devastating the populations
of breeding birds as they go.
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Some islands that are not
naturally connected by sandbars
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have now been joined by causeways, and there
they do not even have to wait for low tide.
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Humans, however,
are no ordinary switching predator.
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The loss of the mega fauna was just
the first sign that they can kill their prey
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at a faster rate than their prey can reproduce.
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Over-harvesting of both animals and plants
is the first of the five ways
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in which we are affecting
the diversity of life on earth.
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As the growing human population devises
ever more efficient technology,
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its ability to over-harvest becomes ever greater.
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Trees illustrate this tendency only too clearly.
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If we cut them down faster
than new ones can grow,
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then a forest will inevitably get smaller
or disappear altogether.
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The natural processes of regeneration
will no longer be sufficient to maintain them.
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This over-harvesting will inevitably
affect all the other species
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that interact with trees or depend on them.
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00:14:26,566 --> 00:14:29,034
Today, trees are being felled worldwide
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ten times faster than
they're being replaced by new growth.
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The sea is being over-harvested too.
70% of the major fish species
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00:14:39,926 --> 00:14:43,760
are now being removed at or above
the rate at which they can reproduce.
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Sylvia Earle is an expert in marine biology.
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We're getting too good
at removing wildlife from the sea.
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Fish have no escape any more.
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00:14:58,886 --> 00:15:02,561
Perhaps there was a time 50 years ago,
certainly 100 years ago,
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when our numbers were smaller
and our ability to capture wildlife in the sea
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was less sophisticated than now, but with
acoustic methods we can find every last tuna,
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every last squid, every last... shrimp in the sea.
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This kind of use of technology is wonderful
in some respects... is terrible in others,
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because it is encouraging us to just take
too much out of the natural systems.
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00:15:34,686 --> 00:15:40,682
Recent figures suggest that each year up to
half of the entire planet's new growth of plants,
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00:15:40,926 --> 00:15:47,001
and a large percentage of animal growth too,
is harvested for the use of just one species,
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our own.
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The second way in which human activities
are changing the diversity of life
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also began, like over-harvesting,
when humans first spread across the globe.
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This is the damage that's caused when
animals and plants are introduced to places
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where they've never lived before.
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Australia is famous
for the number of alien species
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00:16:14,846 --> 00:16:20,239
that have gained a foothold on its land,
often to the detriment of its native species.
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00:16:21,566 --> 00:16:24,444
A dramatic example is the European rabbit.
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Without their natural predators and diseases,
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rabbit populations in Australia
sometimes explode.
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00:16:39,686 --> 00:16:43,998
These rabbits can graze bare
hundreds of square miles of grassland,
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affecting everything else that lives there.
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00:16:51,046 --> 00:16:56,962
Over-grazing eventually affects the rabbits too
and they die of starvation by the million.
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However, alien species cause the most
damage on small oceanic islands,
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00:17:09,006 --> 00:17:11,839
and nowhere more so than on Hawaii.
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00:17:13,406 --> 00:17:18,878
Here, one alien introduction after another
has driven many local species to extinction.
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00:17:19,646 --> 00:17:22,797
When you arrive on Hawaii, it looks wonderful,
it's a tropical paradise.
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00:17:23,166 --> 00:17:27,284
What most tourists don't realise is almost
everything they see there in the lowlands
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00:17:27,486 --> 00:17:32,879
is introduced - there is essentially
no native birds and very little vegetation.
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00:17:33,846 --> 00:17:37,680
Many of those that remain
have become isolated on mountain tops
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00:17:37,686 --> 00:17:40,678
by this tide of introduced animals and plants.
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00:17:44,806 --> 00:17:49,834
Hawaii once had about a hundred species
of birds that were found nowhere else on earth.
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00:17:50,366 --> 00:17:52,516
More than half have gone forever.
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00:17:53,366 --> 00:17:56,278
Many of those that survive
are critically endangered.
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00:17:58,886 --> 00:18:04,438
Snails, better than any other Hawaiian animal,
illustrate how one introduction after another
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00:18:04,526 --> 00:18:06,915
can devastate local wildlife.
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00:18:07,886 --> 00:18:13,438
Millions of years ago, a small number of snail
species arrived here on floating vegetation.
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00:18:13,806 --> 00:18:18,960
From them, over a thousand other species
evolved, all unique to Hawaii.
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00:18:19,886 --> 00:18:23,401
Today, only a small fraction of these still survive.
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00:18:23,726 --> 00:18:27,605
Some that produced these colourful shells
are now so rare
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00:18:27,566 --> 00:18:32,037
that their total world population
number less than ten individuals.
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00:18:33,806 --> 00:18:39,597
These huge collections of Hawaiian snails
are the product of a collecting craze
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00:18:39,806 --> 00:18:41,797
in the late nineteenth century.
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00:18:42,206 --> 00:18:45,801
Many of them will never be seen again;
they're extinct.
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00:18:46,046 --> 00:18:50,722
Some of those were probably driven
into extinction by the sheer intensity
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00:18:50,846 --> 00:18:52,484
with which they were collected.
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00:18:52,286 --> 00:18:55,915
Others undoubtedly have
their population sizes reduced.
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00:18:56,126 --> 00:19:01,325
But the final blow that drove
so many Hawaiian snails into extinction
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00:19:01,886 --> 00:19:04,605
was the introduction of alien species.
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The rat was just one
of the more damaging arrivals,
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00:19:09,646 --> 00:19:13,116
eating its way through the great
populations of ground-living snails
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00:19:13,206 --> 00:19:17,802
and doing considerable damage to those
that lived in huge numbers up in the trees.
224
00:19:18,846 --> 00:19:21,997
Things became worse
with the introduction of pigs and goats,
225
00:19:22,206 --> 00:19:25,039
which damaged or destroyed the plants
on which the snails lived
226
00:19:25,126 --> 00:19:27,720
and so caused many extinctions.
227
00:19:28,966 --> 00:19:32,436
But this was not all. Alien snails now appeared.
228
00:19:34,366 --> 00:19:37,199
These are giant West African snails.
229
00:19:37,246 --> 00:19:40,522
They were introduced into Hawaii
about a century ago
230
00:19:40,606 --> 00:19:43,757
because some people thought
they were particularly delicious to eat.
231
00:19:43,966 --> 00:19:47,754
Unfortunately, snails as big as this
have pretty good appetites themselves,
232
00:19:47,966 --> 00:19:52,756
and before long they were out of control
and chewing up peoples' gardens.
233
00:19:52,926 --> 00:19:58,876
It was decided to try and control them
by introducing killer snails,
234
00:19:59,046 --> 00:20:02,004
including this one from Florida.
235
00:20:01,926 --> 00:20:08,365
Unfortunately, nobody thought to check
whether or not the introduced cannibal snails
236
00:20:08,606 --> 00:20:12,918
would prefer the giant West Africans
or the smaller native Hawaiians.
237
00:20:13,246 --> 00:20:16,682
In the event, they chose the Hawaiian snails,
238
00:20:16,606 --> 00:20:20,804
and so another series of extinctions
began in Hawaii.
239
00:20:22,326 --> 00:20:28,401
These killer snails glide over branches,
looking for the trails left by the native species.
240
00:20:31,886 --> 00:20:35,435
They track them down and then they eat them.
241
00:20:40,966 --> 00:20:46,040
Killer snails are now moving across Hawaii
at the rate of one kilometre a year,
242
00:20:46,286 --> 00:20:48,754
destroying native snail populations as they go.
243
00:20:52,166 --> 00:20:55,078
One might question whether the disappearance
244
00:20:55,046 --> 00:20:59,358
of a range of species of small snails
in Hawaii really matters.
245
00:20:59,846 --> 00:21:05,876
After all, there have been no ecological
consequences or damage, as far as we know.
246
00:21:05,606 --> 00:21:10,236
It could be that we won't be aware
of any damage for some time to come.
247
00:21:10,406 --> 00:21:17,642
But even if there's none, surely it is sad indeed
that our descendants should inherit a natural world
248
00:21:18,086 --> 00:21:21,635
that is more impoverished
than the one we inherited?
249
00:21:22,766 --> 00:21:27,556
The introduction of alien species,
which we often make so thoughtlessly,
250
00:21:27,566 --> 00:21:30,956
is the second way in which
we are damaging life's diversity.
251
00:21:31,886 --> 00:21:36,880
The third and most damaging of all
is the destruction of habitats.
252
00:21:38,606 --> 00:21:43,600
There's a very clear example of the effects
of habitat destruction in South Africa.
253
00:21:44,366 --> 00:21:45,799
This is Cape Town.
254
00:21:47,606 --> 00:21:51,519
Surrounding the city,
on this tiny corner of the African continent,
255
00:21:51,926 --> 00:21:56,158
is a habitat
known by the Afrikaans name of Fynbos.
256
00:21:57,126 --> 00:22:00,004
It's one of the most remarkable
plant communities on earth,
257
00:22:00,006 --> 00:22:05,126
with a higher concentration of species than
even the Amazon rainforests of South America.
258
00:22:06,766 --> 00:22:10,315
It's what scientists call a biological hotspot.
259
00:22:10,526 --> 00:22:14,121
There are more than five and a half
thousand plants growing here
260
00:22:14,366 --> 00:22:16,834
that are found nowhere else on the planet.
261
00:22:17,726 --> 00:22:22,516
It's a remarkable place, too, because
some of the plants here have ranges so small
262
00:22:22,526 --> 00:22:28,556
that the entire world population may be crammed
into an area half the size of a football field.
263
00:22:30,206 --> 00:22:34,836
This peculiarity, sadly,
provides a clear demonstration in miniature
264
00:22:35,006 --> 00:22:37,520
of habitat destruction.
265
00:22:37,406 --> 00:22:42,116
40% of the original area of Fynbos
has been virtually destroyed
266
00:22:42,606 --> 00:22:46,804
by human activities such as agriculture
and the spread of the city.
267
00:22:47,406 --> 00:22:51,445
Clearly, if a plant has a world range
of only a few hundred square metres,
268
00:22:51,726 --> 00:22:55,844
then that area is destroyed,
then the plant will become extinct.
269
00:22:56,766 --> 00:22:58,324
It's a simple idea.
270
00:22:58,686 --> 00:23:02,440
Take away the home of a species
and that species vanishes.
271
00:23:02,606 --> 00:23:05,200
That is habitat destruction.
272
00:23:06,966 --> 00:23:09,321
The damage may not stop there.
273
00:23:09,566 --> 00:23:12,524
Other plants or animals may
also use that patch of land,
274
00:23:12,686 --> 00:23:15,678
or depend on that rare plant,
so they too will be affected,
275
00:23:15,566 --> 00:23:18,603
even if their range is larger
than the area destroyed.
276
00:23:21,366 --> 00:23:25,757
We ourselves are not immune
from the effects of habitat destruction.
277
00:23:28,086 --> 00:23:32,284
There's a startling example of how
that can happen, in the United States.
278
00:23:33,366 --> 00:23:36,676
This is Chaco Canyon,
in the state of New Mexico.
279
00:23:36,726 --> 00:23:40,321
It's part of a desert that covers
hundreds of square miles.
280
00:23:41,526 --> 00:23:46,805
When the first European travellers
reached here, on horseback, about 350 years ago,
281
00:23:46,966 --> 00:23:53,519
they found very little water, hardly any trees
to provide fuel for fires or timber for housing,
282
00:23:53,686 --> 00:23:57,235
and a soil that was very, very infertile.
283
00:23:57,526 --> 00:24:00,882
The place seemed virtually uninhabitable.
284
00:24:00,886 --> 00:24:07,803
Then they entered this canyon and were
greeted by the most extraordinary sight.
285
00:24:22,206 --> 00:24:25,516
This is the settlement of Pueblo Bonito,
286
00:24:25,566 --> 00:24:29,400
and it's just one of a number
of structures in this desert.
287
00:24:29,406 --> 00:24:33,922
They were built about 1,000 years ago
by the Anasazi Indians
288
00:24:34,206 --> 00:24:37,084
and were abandoned a mere 300 years later.
289
00:24:38,206 --> 00:24:41,676
Ever since they were discovered, the same
questions have been asked about them.
290
00:24:41,686 --> 00:24:45,918
Why should the Anasazi
build their cities in a desert?
291
00:24:46,006 --> 00:24:50,158
Why should their civilisation be abandoned
a mere 300 years later?
292
00:24:50,806 --> 00:24:55,357
We now know the answers to those questions
and they still retain the power to shock,
293
00:24:55,606 --> 00:24:58,803
because they are as relevant to our civilisation
294
00:24:58,966 --> 00:25:02,959
as they are to that of the Anasazi
1,000 years ago.
295
00:25:04,246 --> 00:25:07,204
Pueblo Bonito was five storeys high -
296
00:25:07,766 --> 00:25:11,645
the tallest building in North America
until the advent of steel skyscrapers
297
00:25:11,606 --> 00:25:13,597
in the late nineteenth century.
298
00:25:15,806 --> 00:25:18,639
About 215,000 wooden beams were used
299
00:25:18,686 --> 00:25:20,916
in the buildings that once stood in the canyon.
300
00:25:21,686 --> 00:25:26,555
It's not just a question of why
the Anasazi lived here, but how?
301
00:25:26,726 --> 00:25:32,722
Where did they find the trees needed for
the timber for construction work and fuel for fires?
302
00:25:32,966 --> 00:25:36,436
There are signs of fields
and irrigation systems round here,
303
00:25:36,326 --> 00:25:41,320
but the water table is well below the surface
and the Anasazi didn't have pumps to raise it.
304
00:25:41,606 --> 00:25:47,681
It required an inspired piece of detection work
to solve the mystery of Chaco Canyon.
305
00:25:47,846 --> 00:25:53,478
Rather surprisingly, the key to it
was a little mammal called the pack rat.
306
00:25:59,126 --> 00:26:02,118
The pack rat is nocturnal and very shy.
307
00:26:02,006 --> 00:26:05,794
To see it, we have to use
a sensitive night-vision camera.
308
00:26:06,166 --> 00:26:08,157
They live in burrows.
309
00:26:08,086 --> 00:26:11,283
At night, they emerge
to collect sticks, pine needles,
310
00:26:11,486 --> 00:26:13,477
and pretty much anything else they can carry,
311
00:26:13,886 --> 00:26:16,684
which they deposit on a mound
on top of their burrow.
312
00:26:16,526 --> 00:26:19,518
This mound is their toilet area.
313
00:26:19,726 --> 00:26:25,562
Such middens may be used continuously
for over 100 years before being abandoned.
314
00:26:25,806 --> 00:26:31,039
Over time, the nitrogen in their droppings
crystallises and the midden solidifies,
315
00:26:31,246 --> 00:26:35,956
and so can survive for thousands of years
in this hot, dry climate.
316
00:26:36,086 --> 00:26:39,237
Fossil middens are like time capsules.
317
00:26:39,566 --> 00:26:45,243
They carry an accurate record of the plant life
during the time that the midden was created.
318
00:26:45,326 --> 00:26:49,558
Scientists have analysed
the contents of 52 such middens,
319
00:26:49,646 --> 00:26:53,116
which between them cover a period
of 10,000 years.
320
00:26:53,486 --> 00:26:55,841
What they found was a revelation.
321
00:26:57,046 --> 00:27:01,278
By dissolving the crystallised nitrogen
and studying the plant remains,
322
00:27:01,246 --> 00:27:04,044
the history of a civilisation was unravelled.
323
00:27:08,166 --> 00:27:11,522
It was discovered that when the Anasazi
first arrived in Chaco Canyon,
324
00:27:11,366 --> 00:27:14,961
the area was wooded with pinyon
and ponderosa pines.
325
00:27:16,126 --> 00:27:20,438
These trees were cut down
for firewood and for building materials.
326
00:27:24,766 --> 00:27:28,759
When the canyon had been cleared
of all its trees, the Anasazi built roads
327
00:27:28,606 --> 00:27:32,315
to bring timber back from up to 70 miles
away in the mountains.
328
00:27:32,446 --> 00:27:34,835
But by then, the damage had been done.
329
00:27:36,206 --> 00:27:39,164
This is one of the few trees still standing.
330
00:27:39,086 --> 00:27:44,558
It seems that the destruction of the trees,
combined with an ill-timed period of drought,
331
00:27:44,846 --> 00:27:49,966
caused the water table to drop below the level
of the irrigation systems in the fields,
332
00:27:50,126 --> 00:27:52,560
until they could no longer produce crops.
333
00:27:53,006 --> 00:27:58,364
The land became the desert that we know today
and the Anasazi were forced to leave.
334
00:27:59,846 --> 00:28:04,078
The collapse of this civilisation
is in itself an alarming story.
335
00:28:04,166 --> 00:28:06,839
But Chaco Canyon was by no means unique.
336
00:28:07,526 --> 00:28:11,758
There are dozens of examples.
There were collapses in the Fertile Crescent,
337
00:28:11,846 --> 00:28:16,556
on Easter Island, at Angkor Wat,
in the Indus Valley, at Great Zimbabwe,
338
00:28:17,126 --> 00:28:21,358
in Mycenaean Greece, in the Mississippi Valley,
it goes on and on and on.
339
00:28:22,646 --> 00:28:27,845
The destruction of habitats is doing more
damage to biodiversity around the world
340
00:28:28,086 --> 00:28:30,077
than any other human activity.
341
00:28:31,926 --> 00:28:35,555
As our population increases and as
we cover more of the earth's surface
342
00:28:35,766 --> 00:28:38,075
with our buildings and our cultivated fields,
343
00:28:38,166 --> 00:28:41,442
we will inevitably lose more wild habitat.
344
00:28:41,526 --> 00:28:44,086
(ORCHESTRAL MUSIC)
345
00:29:33,966 --> 00:29:36,924
The damage we have inflicted
on the world's environments
346
00:29:36,846 --> 00:29:41,636
has led many to question whether
the human species is deliberately destructive.
347
00:29:51,246 --> 00:29:54,636
Edward Wilson is a biologist
who's made a special study
348
00:29:54,606 --> 00:29:57,564
of the effect of human behaviour
on the rest of life.
349
00:29:57,966 --> 00:30:00,321
(WILSON) I think it would be a grave injustice
350
00:30:00,646 --> 00:30:04,480
to speak of the human species
as in some sense evil...
351
00:30:06,406 --> 00:30:10,957
...even though we are destroying
the environment so efficiently at the present time.
352
00:30:10,726 --> 00:30:13,957
Basically, that's not our intent, it never was.
353
00:30:14,366 --> 00:30:23,001
It was very natural - in fact, it was necessary
for survival for the ancestral human beings -
354
00:30:23,006 --> 00:30:30,276
to throw everything they had against
the wilderness in an attempt to conquer it,
355
00:30:30,526 --> 00:30:35,361
to utilise it... that is the nature of humankind.
356
00:30:35,486 --> 00:30:43,245
To expand the population,
to gain security, to control, to alter,
357
00:30:43,526 --> 00:30:48,520
and for millions of years,
that paid off without undue damage.
358
00:30:48,806 --> 00:30:54,756
But then what happened was,
as we developed a modern, industrial capacity,
359
00:30:54,566 --> 00:31:01,244
then the techno-scientific capacity to eliminate
entire habitats quickly and efficiently...
360
00:31:01,646 --> 00:31:06,800
We succeeded too well
and at long last we broke nature.
361
00:31:06,926 --> 00:31:12,444
And now, almost too late, we're waking up
to the fact that we've overdone it
362
00:31:12,686 --> 00:31:19,319
and we're destroying the very foundation
in the environment on which humanity was built.
363
00:31:20,606 --> 00:31:23,325
(ATTENBOROUGH)
Habitat destruction is the third way
364
00:31:23,486 --> 00:31:26,876
in which human activities
are damaging life's diversity.
365
00:31:29,246 --> 00:31:32,875
A process called islandisation is the fourth.
366
00:31:34,046 --> 00:31:40,679
(LAWTON) When we destroy habitats,
we tend to leave undisturbed pockets.
367
00:31:40,846 --> 00:31:45,966
Whenever you fly over any bit of the globe now,
you can see what we're doing to it.
368
00:31:46,126 --> 00:31:50,597
Basically the process can be
thought of as one of islandisation.
369
00:31:51,246 --> 00:31:57,037
Islands of undisturbed habitat
in a sea of totally modified habitat.
370
00:31:59,126 --> 00:32:03,483
What happens to habitats that have
been cut up and reduced to islands?
371
00:32:03,446 --> 00:32:08,804
To answer that a huge and ingenious experiment
was set up in the rainforests of Brazil
372
00:32:09,286 --> 00:32:11,880
by conservation biologist Tom Lovejoy.
373
00:32:12,406 --> 00:32:16,843
Basically, it's like
you have this carpet of rainforest,
374
00:32:16,726 --> 00:32:19,877
and you took a cookie cutter
and put it down in a few places
375
00:32:20,086 --> 00:32:22,725
and cut all the forests
away around the cookie cutter
376
00:32:23,126 --> 00:32:26,914
and then you were left
with these green patches of forest.
377
00:32:29,366 --> 00:32:32,324
Although the cleared areas
have now begun to grow back,
378
00:32:32,246 --> 00:32:35,875
the regrowth consists
of just a few weedy species.
379
00:32:36,086 --> 00:32:39,601
So the islands of rainforest,
like this dark green rectangular patch,
380
00:32:40,006 --> 00:32:42,076
still remain isolated.
381
00:32:45,286 --> 00:32:50,280
It was found that these islands of forests
changed from the centre to the edge.
382
00:32:50,406 --> 00:32:53,239
Nearer the margins,
the more species will have gone.
383
00:32:53,766 --> 00:32:58,999
Species are continuing to disappear
even 20 years later, due to changed conditions
384
00:32:59,046 --> 00:33:03,597
or because the islands were simply
not big enough to sustain their populations.
385
00:33:07,206 --> 00:33:11,324
The results were usually the same,
whether in an experimental island
386
00:33:11,526 --> 00:33:15,599
or in an area of forest
bisected by nothing more than a road.
387
00:33:19,326 --> 00:33:23,444
One clear example of the effects
of islandisation that has been studied here
388
00:33:23,166 --> 00:33:27,478
involves a group of birds that habitually
follow the swarms of army ants.
389
00:33:29,006 --> 00:33:32,157
Studies have been made to discover
whether these ant birds
390
00:33:32,406 --> 00:33:34,795
will fly from one patch of forest to another.
391
00:33:37,886 --> 00:33:40,525
Ant birds rely for their food on the army ants
392
00:33:40,846 --> 00:33:43,838
which range over the forest floor
hunting insects.
393
00:33:44,006 --> 00:33:47,794
The ant birds follow them,
picking off whatever insects they can.
394
00:33:55,126 --> 00:34:00,200
A colony of ants needs a large area of forest
to provide it with enough insects.
395
00:34:03,526 --> 00:34:09,123
If an island of forest is not big enough,
then the ants will leave and cross to another one.
396
00:34:09,286 --> 00:34:11,846
This presents a problem for the ant birds.
397
00:34:12,686 --> 00:34:18,556
(LOVEJOY) They're psychologically adapted
to staying in dark, shadowy forest.
398
00:34:19,486 --> 00:34:21,795
They simply will not go out in the open.
399
00:34:21,886 --> 00:34:28,564
So they are unable to follow an army ant colony
if it leaves a fragment.
400
00:34:28,766 --> 00:34:32,645
If they are then left in the fragment,
they will starve and die.
401
00:34:34,726 --> 00:34:40,722
One species after another will be lost wherever
you create an island, in any kind of habitat.
402
00:34:42,166 --> 00:34:45,283
You're going through a simplification
of the ecosystem,
403
00:34:45,526 --> 00:34:48,882
an impoverishment of the number of species,
404
00:34:48,806 --> 00:34:54,039
so you end up with something which is
quite less than what you started out with.
405
00:34:56,006 --> 00:34:59,840
Islandisation is happening
more and more around the world.
406
00:34:59,846 --> 00:35:02,280
Even nature reserves are islands.
407
00:35:02,726 --> 00:35:05,763
The smaller an island,
the more vulnerable its inhabitants.
408
00:35:05,606 --> 00:35:09,281
A large species may need
very big islands indeed.
409
00:35:14,046 --> 00:35:17,561
There's a small but clear example
on the chalk grasslands
410
00:35:17,886 --> 00:35:21,925
which once extended right along the whole
length of the downs of southern England.
411
00:35:22,206 --> 00:35:26,677
Changes in agricultural practices here
have had a dramatic effect...
412
00:35:26,766 --> 00:35:28,836
on this little insect.
413
00:35:33,886 --> 00:35:38,482
Like many animals and plants,
the silver-spotted skipper butterfly
414
00:35:38,606 --> 00:35:40,676
is very particular about where it lives.
415
00:35:40,806 --> 00:35:48,565
In England, it can only survive where the grass
is very well grazed, as here at Boxhill in Surrey.
416
00:35:48,486 --> 00:35:54,118
That grazing keeps the grass very short and
allows a full range of downland flowers to bloom.
417
00:35:54,526 --> 00:36:00,396
But more importantly for the butterfly,
it also creates areas of bare earth
418
00:36:00,286 --> 00:36:02,846
where there's no grass and no flowers.
419
00:36:06,886 --> 00:36:11,562
These bare patches of earth are crucial to it
because they warm up very quickly in the sun.
420
00:36:12,526 --> 00:36:16,075
The butterflies bask on them
and so raise their body temperature.
421
00:36:16,766 --> 00:36:21,442
Only when they've done that can they fly away
and lay their eggs on the surrounding grass.
422
00:36:23,966 --> 00:36:29,518
The silver-spotted skipper's home has now been
reduced to a number of small grassland islands.
423
00:36:29,726 --> 00:36:33,685
They won't fly more than a short distance
over unsuitable ground,
424
00:36:33,566 --> 00:36:36,285
and so don't move from one island to another.
425
00:36:36,686 --> 00:36:40,599
So each butterfly population
is now isolated from the others,
426
00:36:40,646 --> 00:36:43,285
a typical consequence of islandisation.
427
00:36:44,486 --> 00:36:48,365
If a bad season or a disease
eliminates one colony,
428
00:36:48,526 --> 00:36:52,360
that area cannot be naturally
restocked from elsewhere.
429
00:36:54,806 --> 00:36:58,640
The danger for species
living in isolated populations
430
00:36:58,646 --> 00:37:02,525
is that one after the other
those populations may die out.
431
00:37:02,486 --> 00:37:04,522
If nothing is done to save them,
432
00:37:04,886 --> 00:37:08,276
then before long the species
has disappeared over quite a wide area.
433
00:37:08,246 --> 00:37:14,765
If its range was not large to start with,
quite soon it becomes totally extinct.
434
00:37:16,686 --> 00:37:21,396
The piecemeal destruction of populations
caused by islandisation of habitat
435
00:37:21,486 --> 00:37:25,195
is the fourth way in which humans
are affecting the environment.
436
00:37:26,566 --> 00:37:29,080
The fifth way is pollution.
437
00:37:36,646 --> 00:37:39,558
There is pollution in many parts of the world.
438
00:37:39,526 --> 00:37:44,202
Its damage to habitat may be great
but often it's only local.
439
00:37:53,366 --> 00:37:58,884
There is one kind of pollution, however,
which could have worldwide consequences.
440
00:37:59,126 --> 00:38:02,596
That is the global warming
that results from human activities
441
00:38:02,966 --> 00:38:05,878
that pump carbon dioxide into the atmosphere.
442
00:38:05,846 --> 00:38:12,081
Carbon dioxide is a greenhouse gas;
that is to say, it traps the sun's heat.
443
00:38:12,086 --> 00:38:16,955
The more carbon dioxide there is
in the atmosphere, the warmer it becomes.
444
00:38:20,206 --> 00:38:24,438
Stephen Schneider is a scientist
who has studied both climate change
445
00:38:24,526 --> 00:38:26,517
and its effects on the natural world.
446
00:38:27,286 --> 00:38:31,484
It's absolutely certain that humans,
when they use the atmosphere as a free sewer
447
00:38:31,606 --> 00:38:33,881
and we dump tail pipes and smoke stacks in it
448
00:38:34,006 --> 00:38:36,395
and chop down trees and have cement plants,
449
00:38:36,406 --> 00:38:38,920
are adding to that envelope of greenhouse gases.
450
00:38:39,446 --> 00:38:43,234
It's virtually certain that that traps enough heat
to make a significant difference.
451
00:38:43,766 --> 00:38:46,439
There are probably damages already.
Sea levels are now
452
00:38:46,646 --> 00:38:50,195
of the order of 10 to 20 centimetres
higher than they were,
453
00:38:50,006 --> 00:38:54,602
mountain glaciers are melting, there's probably
a little added intensity to hurricanes,
454
00:38:54,806 --> 00:38:59,118
so it's already possible to argue plausibly
that we've started to crank up the stress
455
00:38:59,606 --> 00:39:02,120
in terms of added droughts
and floods and so forth.
456
00:39:02,966 --> 00:39:06,561
(ATTENBOROUGH) Global warming has
occurred naturally many times before.
457
00:39:06,326 --> 00:39:10,524
You can see the effect on animals and plants
of just one such happening
458
00:39:10,926 --> 00:39:15,875
if you go a few miles out to sea
and back in time by 10,000 years.
459
00:39:16,526 --> 00:39:20,883
I'm on a fishing boat on the North Sea,
just off the Dutch coast.
460
00:39:21,286 --> 00:39:27,077
We're trawling at a depth
of about 30 metres, 90 feet, for mussels.
461
00:39:27,046 --> 00:39:31,119
Sometimes the nets bring up
something more than mussels;
462
00:39:31,086 --> 00:39:35,762
they bring up vivid evidence
of an ancient global warming.
463
00:39:56,246 --> 00:40:00,444
Starfish, razor shells, starfish...
464
00:40:03,846 --> 00:40:05,996
That's more like it...
465
00:40:09,286 --> 00:40:12,961
That's a bit of bone, and a huge bone, too.
466
00:40:13,206 --> 00:40:15,766
That would have been
an articulating surface, like that.
467
00:40:22,006 --> 00:40:24,884
That looks like... a tooth.
468
00:40:24,846 --> 00:40:28,043
That's a tooth of a small horse.
469
00:40:29,246 --> 00:40:34,604
This is nothing compared with what
has been got out of this particular sea.
470
00:40:35,966 --> 00:40:40,039
Over here, all these have
come out from just here...
471
00:40:41,726 --> 00:40:44,320
A tusk, a mammoth tusk.
472
00:40:47,006 --> 00:40:53,684
This... this is the joint... from the top
of the shoulder, there, like that.
473
00:40:54,686 --> 00:40:56,916
Also of a mammoth.
474
00:40:57,086 --> 00:41:03,559
This, perhaps most convincing of all - nobody
doubted that this is something very strange.
475
00:41:03,326 --> 00:41:06,124
This is a mammoth's tooth.
476
00:41:07,446 --> 00:41:12,804
These are its roots, this is its substantial
body of the tooth that was in the jaw,
477
00:41:12,726 --> 00:41:16,401
and this is the grinding surface.
478
00:41:16,566 --> 00:41:23,278
Spectacular demonstration... that nine,
ten, eleven thousand years ago,
479
00:41:23,366 --> 00:41:29,714
this patch of the sea was dry land,
with mammoths wandering over it.
480
00:41:32,966 --> 00:41:39,041
That global warming led to a great rise in sea
levels which drowned much low-lying land
481
00:41:39,206 --> 00:41:43,722
and changed the character of many areas
by altering weather patterns.
482
00:41:45,206 --> 00:41:49,722
Finding the bones of a great land animal
like a mammoth under the sea
483
00:41:49,806 --> 00:41:55,119
makes it perfectly clear that global warming
can bring about great, profound changes
484
00:41:55,086 --> 00:41:57,236
in the distributions of animals and plants.
485
00:41:57,486 --> 00:42:03,038
Equally obviously, any future global warming
is likely to do the same.
486
00:42:05,646 --> 00:42:09,241
When it happens, temperatures
change all over the planet,
487
00:42:09,006 --> 00:42:11,156
as we can see on this thermal image.
488
00:42:11,406 --> 00:42:14,125
This is a problem for many animals and plants,
489
00:42:14,286 --> 00:42:18,837
because most can only live within
a very limited temperature range.
490
00:42:19,166 --> 00:42:22,044
If climate changes,
they must move to keep pace with it.
491
00:42:22,526 --> 00:42:26,121
For example, when the climate
warmed after the last Ice Age,
492
00:42:26,366 --> 00:42:30,996
oak forests moved north or south,
to keep up with their shifting temperature zone.
493
00:42:31,166 --> 00:42:34,715
How does an oak forest move?
The answer is, very slowly,
494
00:42:35,006 --> 00:42:37,884
by having its seeds transported by animals.
495
00:42:39,006 --> 00:42:43,921
In the autumn, squirrels and jays bury acorns
as food stores for the winter months.
496
00:42:44,406 --> 00:42:48,479
But they forget where many of them are
and those acorns will germinate.
497
00:42:49,966 --> 00:42:54,596
When global warming happens,
acorns buried in the north of the forest will grow,
498
00:42:54,726 --> 00:42:57,604
while those of the south,
where it is too warm, will die.
499
00:42:57,606 --> 00:42:59,915
So a forest slowly creeps north.
500
00:43:01,806 --> 00:43:03,876
This process took thousands of years.
501
00:43:04,126 --> 00:43:09,644
But today it seems that global warming
is happening faster than ever before.
502
00:43:09,806 --> 00:43:14,641
It's not like it was when the Ice Age ended,
15 to 12,000 thousand years ago,
503
00:43:14,606 --> 00:43:19,077
and the trees marched north,
marched in the sense that the seeds spread
504
00:43:19,406 --> 00:43:22,125
and animals literally flew and walked.
505
00:43:22,286 --> 00:43:26,074
Now we're saying, go ahead and redo that,
not in 1,000 years
506
00:43:26,126 --> 00:43:30,244
or in 5,000 years like in history,
but go ahead and redo that in a century
507
00:43:30,446 --> 00:43:34,325
and do it when you have to cross factories,
farms, freeways and settlements,
508
00:43:34,606 --> 00:43:36,676
and all the human disturbance.
509
00:43:37,006 --> 00:43:42,444
It's that combination of factors,
the disturbance combined with the climate change
510
00:43:42,286 --> 00:43:44,516
that makes most of us in environmental science
511
00:43:44,846 --> 00:43:48,725
very concerned about the ability
of the earth to support
512
00:43:48,686 --> 00:43:51,519
anywhere near the current level
of biodiversity in the next century.
513
00:43:53,726 --> 00:43:57,355
These are the five ways
we are damaging the planet.
514
00:43:57,086 --> 00:44:02,877
Over-harvesting, introducing alien species,
destroying the places where species live,
515
00:44:03,326 --> 00:44:08,605
creating small islands of habitat
and finally by polluting the atmosphere.
516
00:44:10,046 --> 00:44:14,995
Change in itself is not necessarily destructive
when it happens slowly.
517
00:44:16,126 --> 00:44:21,359
However, these five factors are all happening
at unprecedented speed.
518
00:44:23,326 --> 00:44:27,001
It seems that the reasons behind
the loss of species today
519
00:44:27,006 --> 00:44:29,156
make the impending change unique
520
00:44:29,406 --> 00:44:33,479
among the great waves of mass extinctions
that have happened so far.
521
00:44:33,526 --> 00:44:38,361
Scientist Sir Robert May is a leading
authority on the current biological crisis.
522
00:44:38,646 --> 00:44:43,276
The dinosaurs were probably done in
through an asteroid impact,
523
00:44:43,446 --> 00:44:46,916
an external environmental impact.
524
00:44:46,806 --> 00:44:50,685
What we're seeing at the moment
is something unique in the history of life,
525
00:44:51,126 --> 00:44:56,280
a single species, us,
sequestering to our use, for example,
526
00:44:56,406 --> 00:45:01,480
a quarter to a half of all the plant material
that grows on earth in any one year.
527
00:45:03,126 --> 00:45:09,759
Our activities are creating the conditions
that are driving this sixth great wave of extinction,
528
00:45:09,846 --> 00:45:12,644
the wave on whose breaking tip we stand.
529
00:45:13,126 --> 00:45:16,562
It's both literally the best of times
and the worst of times.
530
00:45:16,966 --> 00:45:19,764
There has never been a more
exciting time to be alive,
531
00:45:19,846 --> 00:45:24,124
when we're beginning to actually
read the book of life itself.
532
00:45:26,086 --> 00:45:29,044
We have the potential
to apply that understanding...
533
00:45:29,446 --> 00:45:35,078
for good stewardship and husbandry
of this marvellous world that we're heir to,
534
00:45:35,206 --> 00:45:39,643
or we can just thoughtlessly bend it,
to creating more...
535
00:45:40,966 --> 00:45:43,480
bits of garbage to amuse ourselves.
536
00:45:45,126 --> 00:45:49,085
I don't think there's going to be some
major environmental catastrophe,
537
00:45:48,966 --> 00:45:52,720
some major Armageddon,
the world isn't going to stop tomorrow.
538
00:45:52,806 --> 00:45:58,119
The world will simply become a progressively
grottier, less interesting place.
539
00:45:58,566 --> 00:46:07,042
If you like... rats and... cats and... house finches
540
00:46:07,206 --> 00:46:11,643
and a few things like this and you would
like to see them everywhere you go,
541
00:46:11,526 --> 00:46:16,077
then biotic impoverishment is for you.
542
00:46:16,326 --> 00:46:21,844
But if you or your descendants would like to live...
543
00:46:23,526 --> 00:46:28,600
in an interesting world in which
there is richness of life, a variety of life,
544
00:46:28,806 --> 00:46:35,041
and wild environments full of surprises
and aesthetic delight,
545
00:46:35,046 --> 00:46:40,359
then... conservation of biodiversity is for you.
546
00:46:41,166 --> 00:46:47,002
My belief is... that given enough education,
enough awareness,
547
00:46:47,326 --> 00:46:51,365
enough sensitivity...
548
00:46:51,646 --> 00:46:54,956
to problems presented to them,
549
00:46:55,006 --> 00:47:02,276
people have the capacity to do amazing things
and change their attitude.
550
00:47:08,566 --> 00:47:14,038
We began our investigation in Hawaii,
the very image of a tropical paradise.
551
00:47:14,206 --> 00:47:18,757
The vulnerability of its native animals and plants
had much to do with the fact
552
00:47:19,006 --> 00:47:24,683
that they evolve on islands, but nonetheless
their fate should be taken as a warning.
553
00:47:25,446 --> 00:47:31,123
We now understand which of humanity's
activities inflicts the greatest damage
554
00:47:31,206 --> 00:47:33,845
on the diversity of animals and plants
on this planet.
555
00:47:35,246 --> 00:47:37,521
That knowledge is going to be crucial
556
00:47:37,646 --> 00:47:40,922
if we are to meet the great challenge
of the next century:
557
00:47:41,006 --> 00:47:46,034
How to provide a good living standard
for an ever-growing number of human beings,
558
00:47:46,286 --> 00:47:51,485
without inflicting a grave impoverishment
on the planet.
559
00:48:15,926 --> 00:48:19,521
In the next programme, we will discover
how changes in our behaviour
560
00:48:19,766 --> 00:48:23,202
could prevent a great loss of species
over the next century.
561
00:48:23,126 --> 00:48:26,004
Our journey will take us to the mountains
of New Guinea,
562
00:48:26,526 --> 00:48:28,960
home to the largest butterflies on earth.
563
00:48:30,006 --> 00:48:34,045
We will visit the grasslands of Africa,
with their famous big mammals.
564
00:48:34,326 --> 00:48:39,275
In the forests of the American north west,
we will see the beautiful spotted owl.
565
00:48:39,446 --> 00:48:43,234
Finally, on the single
most remote island on the planet,
566
00:48:43,246 --> 00:48:47,478
we will discover how our own past
can offer us important lessons for the future.