(STEVE LEONARD ) Midwinter at the bottom of the world - Antarctica -
the coldest place on Earth,
with an air temperature of minus 50 degrees centigrade,
You'd think that nothing could survive here,
Yet, huddling together, somehow these emperor penguins
have evolved to cope with the battle for life in the big freeze,
But cold is not the penguins' biggest enemy,
This is,
The leopard seal - four metres long -
a super-predator,
(PENGUINS SQUAWK)
No wonder everyone's reluctant to be the first to take the plunge,
Penguin and seal have a relationship forged over millions of years -
that of predator and prey,
It's easy to see nature as red in tooth and claw, where predators dictate who lives and dies
and only the fastest and strongest survive,
But the truth is, predators and prey are just part of life's story,
Our world is made up of a vast network of different relationships,
Animals, including us, have to find mates, look after families
and keep up with the neighbours,
And all these relationships affect how we look and behave,
(ROARS)
(SCREECHING)
This is the surprising story
of how the relationships between all living things have shaped the whole journey of life,
Life on Earth wasn't always as complicated as it is today,
There was a time when there were no relationships,
There was no violence,
practically no competition,
and no sex.
Imagine that.
Three billion years ago, the pinnacle of evolution was these strange lumps on the ocean floor -
stromatolites, made up of ancient algae,
It might not have the ring of the “age of the dinosaurs”,
but the age of the stromatolites was eight times longer
and was the longest period of peace and tranquillity that life has ever known.
They might not look much, but stromatolites had the power to change the world,
For the first time in the history of the planet, they produced a gas called oxygen,
and so totally transformed the planet's atmosphere,
Not only did they generate the air we breathe,
they set the scene for all life as we know it today,
Because of them, a brand-new type of cell evolved,
perhaps the most important life has ever known,
These revolutionary oxygen-fuelled cells spawned our ancestors,
but they were 20 times more energetic than the older models,
Some discovered that the quickest way to get the extra energy they needed
was to steal it by engulfing other cells,
A new force was unleashed - the predator,
(PANTS)
With predators around, you’ve got to be able to defend yourself.
One way is to make yourself invisible.
Armour’s good, too.
Good solid protection.
Staying alert can mean the difference between life and death.
As predators find better ways to catch and kill,
their prey have to improve their self-defence,
The two are locked in an intense relationship which forces both sides to change
because neither can afford to be left behind,
Nature selects only the winners’ genes,
The losers will disappear,
This arms race has helped shape the lives and bodies of just about everything alive today
and pushed some creatures to incredible extremes,
This cricket might think it's on a flower...
..but it's actually a mantis that's evolved to look just like an orchid,
Beauty turns out to be a beast,
Other hunting strategies are even more bizarre,
Over millennia, the snapping turtle's efforts to reel in a fish
have turned its tongue into a juicy worm,
But secret weapons aren't the only winning formula,
Sometimes, more subtle tactics may be what you need,
Meet jumping spider Portia, one of the world's smallest assassins,
She's hunting the much larger web spider,
She might be tiny, but she has a big appetite,
Her first direct approach alerts her target, who shakes the web and forces Portia to retreat,
But Portia has evolved a plan B -
a manoeuvre straight out of “Mission: Impossible”,
She slowly lowers herself within striking range...
..leaps, bites...
..and leaves the poison from her tiny fangs to do the rest,
This time, it isn't size or secrecy that counts, but strategy,
Portia may be small, but she's as deadly as they come,
The relationship between hunter and hunted
doesn't only shape the way that predators attack, it drives the way that prey fight back,
Sometimes, it's just about using your natural assets in a different way,
When a hungry raven eyes their chicks, fieldfares fight dirty,
They drop bombs,
(CAWS)
A dirty trick but, hey, it works,
The only problem with an evolutionary arms race is that we don't see it develop.
All we see is the end result.
But there are rare exceptions, like the story of the passion flower.
Like other prey species, they're evolving to protect themselves,
but what makes them unique is that you can watch them doing it.
Plants have to fight for survival, too, and even these exotic passion vines have enemies,
At home in tropical America,
they're under constant attack from lethal predators that live deep in the jungle -
heliconius butterflies,
The adults are harmless enough, It's what they leave behind them that's the problem,
Mother butterflies lay their eggs on the passion vine's leaves,
Tiny time bombs...
..which soon hatch out into very hungry caterpillars,
This plant's fate is already sealed,
In a few days, there will be nothing left,
If a passion vine already has a batch of eggs installed, it's pointless to lay more,
A sensible mother butterfly will pass it by, which gives the passion flower a chance to fight back,
Today, not all the eggs are quite what they appear,
Some are in fact just yellow spots grown by the passion flower to deter mother butterflies,
But in this mini arms race, not all attacks are foiled,
Some passion flowers haven't quite got it nailed.
These spots are supposed to be butterfly eggs,
but it hasn't quite put off all of the butterflies,
because we've got a very greedy caterpillar.
So there's pressure for ever better mimics to evolve,
Some are now so good, it's hard to tell which eggs are real,
False,
Real,
False,
And real,
Who'd have thought that the relationship between a butterfly and a vine
could produce such a sophisticated bluff?
But trouble can come at you from all sides.
Even when you’re safe from predators, you can often have strife from your own kind -
competition.
In a rainforest, of course, the plants are all after the same thing - precious light,
And they can't all be winners, Only those best adapted to compete survive,
It's the same principle wherever there's a crowd, In Africa, meat is the prize,
A vulture has the aerial advantage that means it can spot the first signs of a kill,
but it won't have long to feed undisturbed,
Before long, every vulture in the area is fighting for a beakful,
At this buffet, now only the toughest get to eat,
Lappet-faced vultures are the biggest bully boys of all,
They knock the smaller griffons flying,
But a free lunch attracts other hopefuls, too,
More feathers fly as even lappets have to make way for the mammal heavy mob,
(SNARLING AND SCREECHING)
Like predators and prey, this kind of competition is a real force to be reckoned with -
another influence on evolution which selects only the toughest to survive,
Competition is so crucial to animals' lives
it can have a massive impact on their body shape,
Browsers have been moulded into different shapes and sizes
so they don't tread on each other's toes,
Tiny dik-diks can nibble around the thorny lower branches
in a way no bigger animals can, so they don't need to reach higher than a couple of feet,
Taller impala have control over the acacia's middle zone,
But even they are kept in their place by the gerenuk,
which has a poise no other antelope can match,
Gerenuks look more like ballet dancers than gazelles, They even balance on their pointes,
Their specially adapted hips and spines enable them to swivel vertically
and stand tiptoe on their hind legs,
But there's one animal who can feed even higher still - up to six metres,
It has a flexible leathery tongue
which it can use like a hand to pluck the highest twigs and leaves,
thanks to evolving the longest neck in the world,
The giraffe,
So competition hasn't just pushed animals into developing different eating habits,
it's helped create different species that can live together in harmony,
But what happens when neighbours want exactly the same thing?
Ringtailed lemurs live in troops on the island of Madagascar,
Each group needs their own territory to survive,
for shelter, food and a safe place to rear their babies,
but they're often under threat from other lemur gangs..,
..who'll steal the whole thing if they can,
- (SCREECHES) - The alarm sounds,
These intruders look like they mean business, Time to rally the troops,
Lemur society is run by females, so it's they who lead the band into the fray -
soldiers with babies on their backs,
(DIN OF SCREECHING)
When competition gets this intense, the lemurs' answer is teamwork,
(CHIRPING)
Once animals are driven to work together, the close relationships which evolve
can open up a whole new way of life,
Meerkats are high on the menu for many predators...
..so they work together to protect themselves,
They're one of the few mammals that take turns at doing different jobs,
While the rest of the family digs for breakfast, one member stands guard,
looking out for predators,
The others feel safe in the knowledge that someone is watching their backs,
(CHIRPING)
And it's not just lookout duty meerkats share,
When a monitor lizard appears, they all gang up to drive it away,
En masse, these little creatures make a formidable force,
(CHIRPING)
Being such good team players is the meerkats' winning formula,
It's all for one and one for all,
It's easy to see why we help our relations, but some animals co-operate with different species,
How could that evolve?
There's an answer to be found in the sea,
A coral reef like this is a natural metropolis,
where everyone is trying to get on and make their own way.
It's full of opportunities, deals to be struck...
Some enterprising characters are cleaning up,
It turns out there's a market niche for professional groomers,
Cleaners - like this tiny wrasse - snaffle up their clients’ parasites and dead skin,
They set up their own cleaning stations,
Customers come from far and wide for dental hygiene or a gill wash,
In return, the cleaner gets a meal,
Cleaner shrimps, too, serve a most discerning clientele,
Fish are smarter than you might think, They have good memories,
and come back regularly to be pampered in exactly the same spot,
and by the same cleaner,
The coral crowd soon learns which are the top salons, boasting the most talented staff,
It's not just tropical fish who've discovered that hiring a little help
can help you get ahead,
Some plants have, too,
This garden only exists because of an ancient alliance between insects and plants.
It's a real match made in heaven
as it's produced some of the most beautiful of all living things - flowers.
Since flowers can't move around,
they need help to carry pollen between them so they can produce fertile seeds,
So they advertise themselves as nectar feeding stations,
As the insects feed, they get an extra takeaway of pollen,
It's an evolutionary partnership that has proved so successful,
flowering plants now dominate our world,
To guarantee delivery,
some flowers have developed an exclusive contract with their pollinators,
Orchids, the royal family of flowers, can be very demanding indeed,
Some, like this bucket orchid, seem downright cruel,
This euglossine bee has to visit the bucket orchid,
He needs its perfumed oils to use as an insect aftershave to attract a mate,
But as he gathers the oil, he loses his grip -
exactly what the orchid wants,
It has evolved a complex trap which press-gangs male bees into service,
The only way out is via the back door and the orchid's pollen sacs,
The pollen sticks to the delivery bee's back,
Once free, he takes a short while to dry off,
Surely he'll never go near a bucket orchid again!
Either male bees have short memories or run out of aftershave,
because here he is falling for the same ploy all over again,
The difference this time is that he's delivering pollen instead,
No question who's wearing the trousers in this relationship,
Although the bond between flowers and insects has extraordinarily beautiful results,
plants also depend on an invisible partnership which is even more important,
Because without it, most of them wouldn’t even exist at all.
They need it to grow, and some plants, like these guys here,
grow very big indeed!
Californian redwoods are the tallest trees in the world,
They can live for more than 2,000 years
and grow more than 300 feet tall,
These are some of the largest of all living things, but they rely on the tiniest of partners -
partners so small that they're almost invisible -
and if I am to stand a chance of seeing them at all,
I've got to go all the way back down there.
They're microscopic and they live hidden underground amongst the tree's roots.
These secret partners turn out to be fungi,
They penetrate the tree's roots,
then stretch out through the soil as a network of tiny threads,
The giant trees can't get enough water and nutrients on their own,
but the fungal network can,
Its massive surface area sucks up the fluid and minerals the trees need
and then transports them back up to their roots,
And what do the trees do for the fungi in return?
Just feed them sugars from their leaves - not a bad deal!
90% of all plants live with fungal partners,
from the redwoods to the rainforests,
It's a 400-million-year-old marriage,
It's possible that without it, plants might never have been able to colonise the land,
And without all this green stuff, where would all we animals be?
The close relationship between plants and fungi is just one of the great alliances to shape life.
There is another - you need a microscope to see it,
It's perhaps the most important partnership on Earth,
It provides the power for nearly all living things, driving every cell in or bodies.
And it's what gives animals their energy,
(MUSIC)
Scattered through the cells of all our bodies
are billions of mysterious structures called mitochondria,
Each is a tiny furnace that releases energy from our food
and generates the life force that our bodies need,
Whoa.
Animals like me and all these guys
can only exist because of the energy the mitochondria release.
It's a crucial relationship and one with very unusual beginnings.
In fact, it didn't even start as a partnership.
Come on, then, big man.
Billions of years ago, the mitochondria lived independent lives as free-floating bacteria,
but our ancestor cell changed all that,
It engulfed one, but instead of eating it, our ancestor formed an alliance with its prey,
The two joined forces and were transformed,
The bacteria became a mitochondrion
and together they created a new type of hybrid super-cell..,
..a super-cell which was the basic building block for almost everything alive today,
So could this mean that it is co-operation and not conflict
which is actually the strongest force in evolution?
Is the fight for life more the embrace of life?
It's a lovely idea.
(CONTENTED SIGH)
But relationships, they're never straightforward, are they?
Most grazing animals in Africa are plagued by biting insects and ticks,
They also have what seem to be whole squads of helpful hangers-on,
Oxpeckers - insect-eating birds who reach the parts the animals themselves can't,
But oxpeckers aren't quite as innocent as they appear,
They don't just eat up ticks, they peck holes in the animal's skin,
What appear to be honest little helpers, in fact turn out to be blood-sucking parasites.
A way of life which, rather horrifyingly, is far more common than you might expect,
Over half of all creatures alive today are parasites -
an insidious hidden force that has infiltrated just about every other living thing.
The Natural History Museum in London
has one of the largest collections of biological specimens in the world..,
..including some particularly gruesome parasites, all now, thankfully, pickled in alcohol,
Having a relationship with a parasite is very much a one-sided affair.
This might look like pasta but it is, in fact, a tapeworm from a killer whale.
Its natural home is inside the intestine of the whale, robbing it of its food.
They can grow to 60 feet in length.
Imagine that inside your gut!
Which is perfectly possible,
This tapeworm can take up residence in humans too,
This is a human botfly larvae.
It's smaller than the tapeworm but it's much more gruesome.
It burrows into the living flesh of people. Victims of this parasite
say that they can hear it munching away in their skin.
This was surgically removed from someone's head.
If you’re going to pick a parasite to play host to, this is not the one to choose.
But parasites aren't just gruesome.
Because they affect virtually every plant and animal alive,
they may just be the biggest influence on the whole of evolution.
Can that really be true?
Well, take rabbits for example,
You might expect predators to be the biggest influence on their lives,
After all, they're hunted by a whole army of killers,
But with predators, they can at least run away,
Rabbits face another threat which they can't see, smell or hear,
Each rabbit is infested with thousands of fleas, ticks and minuscule mites,
which may be small but pack a powerful bite,
These bloodsuckers sap the rabbit's strength, but within them, they carry a deadlier threat,
These little wild baby rabbits have been abandoned by their mother,
but they've been very fortunate because they've been adopted by a human.
Not only have they escaped predation,
they've also been saved from the biggest rabbit killer - the myxomatosis virus.
A virus is a nightmare straight out of a science-fiction movie,
It's an invader with one aim - to replicate,
It contains special components which enable it to fulfil its mission,
A potential victim - the outer surface of a body cell,
On first contact, the virus docks, and merges with the cell membrane,
Its inner pod enters the cell, seeks out the command centre - the nucleus -
and then injects its secret weapon - a snake of virus genes,
These then corrupt the cell, making it into a virus factory,
Eventually, the cell dies and bursts, releasing thousands of new viruses,
and the real destruction begins,
Each year, just about every baby rabbit born in the wild will catch this deadly virus.
Typically, it kills for out of five.
That means in a litter like this, only one would survive.
Viruses are a truly fearsome evolutionary selection force,
far more deadly than predators or competition,
Every living thing has to evolve to fight off viruses - or risk extinction,
I'm talking about warfare on a cellular level which affects all species alive, including us.
In 1918, at the end of the Great War, a flu virus struck Europe,
The war killed 25 million people over four years -
that's three times the population of London -
but the flu epidemic wiped out the same number in just four months,
A virus can wipe out a population and can even threaten an entire species.
So, against such a powerful enemy, how can anything possibly fight back?
The answer is a major obsession for many species on this planet, including ourselves -
it's sex.
How can sexual relationships have anything to do with the fight against parasites?
Surely sex is just a matter of reproduction?
(GROWLS)
You’d be surprised. It turns out there's a lot more to sex than just making babies.
There are lots of living things that reproduce without it, by cloning.
Look at this spider plant. It's grown babies just ready to drop off and start growing.
They're perfect mini versions of the mother plant.
No need for sex at all, and it's such a neat trick, that many animals do it, too.
Aphids are baby machines,
They don't need to have sex with a mate
because they can pump out new aphids all by themselves -
one every 20 minutes, each already full of their own future daughters,
Cloning is great for increasing numbers, but it has one flaw,
As all cloned babies are identical,
a single killer bug could wipe them all out,
The key thing sex does is create variety.
It's like me and you. We're both basically the same, but we are subtly different.
We're individuals.
It's a pattern that's repeated for all kinds of different animals, from people to puppies,
like these little bull terrier puppies. Ah, yes!
Even within one mating, you get incredible diversity,
as you can see in this litter.
They all have the same mum and dad, so how come they're so different?
It's all to do with the secret magic of sex,
During sexual reproduction, the genetic material is reshuffled,
Every sperm and egg is unique,
so when the two join together to make a puppy, every puppy is born unique, too,
They all look different,
but what's critical in the fight against parasites are the differences you can't see,
These puppies' bodies are unique on the inside too,
This one might be more resistant to parvovirus than the rest of them, yes!
And this one might be more resistant to distemper virus.
And it's the same for you and me with human diseases, too.
Wha-ha-ha.
Yes, there you go.
Resistant individuals have cell membranes which lock the killer virus out,
so its lethal life cycle can't get started,
This is why sex is so crucial. Because we're all born so different,
we present a different challenge to the parasites, increasing or chances of survival.
It's like genetic roulette, with every new generation keeping the killer bugs guessing.
No wonder animals are so desperate to have sex,
It's evolution's way of future-proofing new generations,
(WHINING, HONKING CALL)
But to have sex, you do need a relationship, however brief,
(HONKING)
And many animals go to a lot of trouble to make sure they find a mate,
(WHINING, HONKING)
This element of choice
means sexual relationships can have a huge effect on animal evolution too,
Once a year in autumn, American elk gather together to breed,
It's called the rut - a spectacle where stags compete for breeding rights,
This rut is played out in a most unusual location,
In the mammoth area of Yellowstone National Park,
manicured lawns like this attract the herds into the centre of Yellowstone village itself.
Here, humans get a ringside seat,
Each stag has two aims - to impress the females
and to frighten off rivals,
Although the males are much bigger and more dominant,
it's the females who really run this show,
Like females the world over, they'll be left holding the babies,
so they're very choosy about who they mate with,
Only the real studs with the most impressive antlers and fighting ability will do..,
..which forces the males to prove themselves,
It's a knock-out contest where only the winners get the right to breed,
So over generations, the battles get harder and the stags stronger,
Female choice means sexual relationships can shape the bodies and behaviour of their mates,
so they are driving evolution,
The males get so charged up when they're fighting over females
that they'll perceive anything as a threat.
(WHINING CALL)
The overwhelming urge to win and pass on their genes can push the stags over the edge,
Thankfully for us males, there are other less violent ways of courting favour.
Sometimes, it's all just a matter of appearances.
One doesn't always have to fight to prove one's worth - often, it's a matter of showing off,
So some males put all their effort into how they look,
Posers can be just as successful as fighters.
Instead of proving their worth on the battleground,
these peacock males flaunt fancy dress instead,
The females will only mate with the ones they find the most attractive,
But does all this ostentation and display actually mean anything?
How can a female be sure she'll have good, strong, healthy babies?
Are good looks all they're cracked up to be?
Remarkably, a little finch proves that masculine beauty is not just skin deep.
Zebra finch males are very colourful, with orange legs and cheeks and bright red beaks,
The females are much plainer,
So why are the males so colourful?
Let's try a little experiment,
The male's red legs and beaks are full of colour pigments called carotenoids,
found naturally in fruits, seeds and carrots,
So here, I'm going to feed half the males a diet high in carotenoids to make them redder..,
..and then put them in a special choice chamber
next to a duller male who hasn't been fed the pigments,
Two males in their own designer bedrooms at the back, one female at the front,
The sexes are segregated by a pane of glass,
The males can't leave their rooms, but the female can move from one side to the other,
She can choose a male by perching by his window,
either on the left or on the right,
Tiny cameras are installed to record what happens throughout the little bird house,
This high-speed CCTV footage shows what happens next,
Watch the female at the bottom of the screen,
She seems to have chosen the male on the left,
And the camera in his bedroom shows she spends most of her time with him..,
..while another camera reveals the other guy is ignored,
And who do you think is the most popular? The male with the redder beak,
In fact, in these tests, nine out of ten females preferred him,
But why would they fancy the most colourful male?
Well, the same red pigments not only make the male look good,
they help his body fight diseases, too,
A dull male is probably weaker, and not a good bet as a mate,
Bright colours are an honest indicator of health,
so pretty males do turn out to be a good choice as mates after all.
So the next time your mother says “Eat up your vegetables,” it's a good idea to listen to her.
Especially if you’re male.
A brightly-coloured male is not just likely to be healthy,
he'll also pass on his parasite-fighting genes to his babies,
So it pays for a girl to demand the best,
and this male zebra finch has passed his medical with flying colours,
But there's an extra twist,
Researchers now think that girl power can even create new species - but how?
This guy can give us a clue.
He's a zebra cichlid, and experiments have shown he's a dedicated follower of fashion.
These fish are only found in Lake Malawi in Africa,
What makes them special is that males come in a variety of technicoloured coats,
which is extremely unusual in a single species,
It was a mystery as to why the males came in so many different colours.
They certainly weren't evolving to hide from predators, or adapting to local conditions.
Something else was going on, and that something was the females.
To find out more, we put the fish in choice chambers,
The larger, more colourful males are confined,
but the little brown females can swim where they like,
All they have to do is swim in with the male they fancy most, and their choice is made,
The tests have produced some rather surprising results,
It turns out even females of the same species have different ideas about what is sexy,
Some prefer white males,
some yellow, others blotchy, and so on,
Which explains why zebra cichlid males come in so many different colours,
But how does that help to create new cichlid species?
This is where the girl power bit kicks in,
If a group of females gang together and decide that one colour is now highly desirable,
they'll only mate with those particular males,
This preference is passed on to their daughters,
Over generations, an entirely separate breeding group is formed,
and eventually a new type of cichlid,
Girl power not only helps to create beauty,
it also leads to amazing variety
and, ultimately, new species.
Lake Malawi and the other African Great Lakes
started out with just a handful of cichlid species,
Now they're home to one in ten of all kinds of freshwater fish on the planet,
An incredible 1,700 cichlid species
all fashioned by female choice,
This is the greatest explosion of new species ever discovered,
all driven by the relationship between females and their males,
The truth is, of course,
that sexual relationships are only one of the many interactions between living things
that have the potential to shape and drive life.
Whether with families and friends, competitors or enemies,
living together isn't always easy,
But relationships have been a massive force for change throughout the whole journey of life,
And ultimately it's our connections with each other
that have created the spectacular variety of life we see today,
Next week on the “Journey of Life”,
I'm going to retrace our five-million-year journey from ape to human
and discover how we very nearly didn't make it,