(STEVE LEONARD) Imagine the freedom, the buzz, the excitement of taking to the skies,
If only I could,
Being able to fly is something that humans have always dreamed of,
but for two-thirds of the animals alive today, it's a reality.
Flight is one of the greatest breakthroughs in the whole story of evolution.
I'm going to find out how life achieved the miracle of flight,
Over millions of years,
a string of evolutionary accidents created wings not once but several times,
and in very different ways,
Oh, yes! Look at you.
Flight is a unique weapon,
Mastering the skies leaves earthbound creatures at your mercy,
Where there's a black eagle on the wing, rock hyrax need to be alert to aerial attack,
But wings aren't just about extra strike power,
Flying is the fastest, most efficient way to travel,
It allows you to find food, explore new territory, or escape from danger,
So there were lots of good reasons for life to get into the air - the trick was how to do it,
There's one big problem facing any animal that wants to fly.
Gravity.
And to fly, you’ve got to find a way to defy it.
So, in the journey of life, who was the first to conquer gravity and get airborne?
500 million years ago, animals took their first steps onto land,
The pioneers included millipedes, scorpions and spiders,
But while these creatures crawled over the earth, the skies remained empty,
Life stayed grounded for at least another 100 million years..,
..until one group of animals finally made the breakthrough,
The insects.
The first animals ever to fly.
But how did they sprout wings?
One idea is that it's all because insects love to sunbathe.
Insects are cold-blooded,
They need heat from the outside to warm themselves up and move around,
They often bask in the sun,
and maybe in the past, one bug developed small flaps on its back to help soak up the rays,
like mini solar panels,
Purely by chance, these panels may also have helped the insect to be carried by the wind,
Perhaps the panels then evolved into a more aerodynamic shape, eventually becoming wings,
But there's a flaw in this theory,
Insect wings have complex hinged joints, worked by muscles and tendons,
Could they really have evolved from those simple fixed panels?
There is another explanation as to how flight began,
It all started not in the air but in the water.
Many insects spend the first part of their lives submerged,
They breathe through gills, pumping them up and down to take in oxygen,
It's thought it was gills like these that gradually turned into wings,
But how could such a dramatic change take place?
One insect living in the rivers of North America holds a clue,
Stonefly larvae spend almost a year underwater,
then emerge in late winter to start their adult lives,
The adults live just a few days, and their sole purpose is to breed,
But to find a mate, they have to make a death-defying crossing to the shore,
Their wings are far too weak to fly..,
..but they do make good sails,
Perhaps this is how flight began,
An ancient insect waved its gills to catch the breeze and set sail,
just like stoneflies do today,
Gills already had the joints and muscles to flap up and down,
and could then have evolved from sails to wings,
And then, insects really took off,
Whatever that first flying insect was, it won the biggest evolutionary jackpot of all time,
Its genes were now unstoppable,
and today its legacy is around 10 million flying insect species -
the most successful type of animal on Earth,
Ancient fossils have shed light on some of the oldest aerial pioneers,
Among them is one design that's really stood the test of time,
Dragonflies have been around for more than 300 million years,
They were already on the wing
when our four-legged ancestors were still crawling around in swamps,
Dragonflies are the Red Barons of the insect world - fast, agile aerial aces.
These are male emperor dragonflies, and they're fiercely territorial,
When rivals meet, they test each other's flying skills to the limit,
These dogfights can be vicious, even deadly,
Dragonflies are among the largest, fastest insects on the planet,
but compared to some, these modern ones are midgets,
Go back 300 million years..,
..and things were very, very different.
Then there were giants,
Dragonflies with two-foot wingspans - the size of a hawk,
How did such mega-bugs stay in the air?
Well, there was one big difference back then, one that could turn me into a super-athlete,
The atmosphere was supercharged with oxygen,
There was almost twice the amount there is today to power those monster wings,
Dragonflies are still dazzling fliers,
but the best stunt pilot of them all is smaller and much less glamorous,
(BUZZING)
Ever tried to swat a fly?
Tricky, isn't it?
They really are the most amazing of all flying animals.
And one of the most annoying.
Their manoeuvrability is unrivalled.
And their reactions are 12 times faster than or own.
So what's their secret?
Well, bizarrely, it's because their ancestors gave up a pair of wings.
(BUZZING)
Like dragonflies, all early insects had two pairs of wings,
In one type, the hind wings shrank, evolving into tiny rod and ball structures called halteres,
They have become precision instruments,
They work a bit like gyroscopic stabilisers on a modern helicopter or plane,
Flies come in a great variety of shapes and sizes,
They include the hoverfly, crane fly, mosquito,
and our friendly housefly,
and they all have halteres,
Halteres give the fly precise feedback on its position,
helping it make split-second adjustments without losing control,
So it can dodge a swipe and instantly regain perfect poise,
Love 'em or hate 'em, you’ve got to admire 'em.
There are now more than 100,000 kinds of fly,
Their duck and dive design has let them take over the world,
and though they're small, they have a massive impact on other life, including us,
In fact, flies are the most dangerous animals on Earth,
responsible for more human deaths than any other creature,
They carry and spread disease, and because they're so small and manoeuvrable,
it's impossible to escape from them,
Having the top technology for flight isn't the only thing that's made insects such a success,
It's also about when to fly.
It's hard to believe that this and this are the same animal.
(MUSIC)
Why does such a gorgeous creature have such weird and wingless offspring?
It's because its life is split in two - one part for eating and one for breeding,
Caterpillars are munching machines, Their only purpose is to eat and grow,
At this stage, having wings would just get in the way,
A caterpillar can balloon to an incredible 2,000 times its starting weight,
That's like a human baby gaining eight tons in a month and becoming the size of a bus,
Once it's finished gorging,
the caterpillar uses all those calories to make a stunning transformation,
From ugly bug..,
..to winged beauty,
The adult has a very different mission -
to attract a mate and lay its eggs far and wide,
Wings make this job much easier,
and one species of butterfly has taken air travel to extremes,
This is the monarch, long haul operator of the insect world,
It's late summer in Canada,
and these are great-great-grandchildren of monarchs that flew north in spring,
Now they're ready to embark on one of nature's most miraculous journeys,
Triggered by shorter, cooler nights, they head south,
flying the entire length of North America and beyond,
(MUSIC)
Finally, having flown 3,000 miles,
the monarchs reach their winter destination in the mountains of central Mexico,
Somehow, they find their way back to the same trees used by previous generations,
Millions clustered together for safety and warmth,
Insects flew unchallenged for about 100 million years..,
..but another twist of evolution would bring about a second wave of flight,
Skulking in the undergrowth was the ancestor
of some of the most successful fliers ever that would dominate the skies for 150 million years.
The smallest would be little bigger than a sparrow,
and the largest, the size of a light aircraft - the biggest animal ever to fly.
They were the pterosaurs,
Sadly, there are none left to help us piece together their story,
but what we do know is that they evolved from an ancient kind of reptile.
But how did a for-legged reptile turn into one of nature’s most magnificent fliers?
Today, there's a tree-dwelling reptile that offers a clue,
For a green iguana cornered in the treetops, there's just one way out -
straight down!
They generally hang out over water for a safer landing,
A simple free fall isn't very stylish, but it is a start,
If you can add some control to your descent, then you're a step closer to taking flight,
In the forests of south-east Asia lives an animal that's done just that,
This gecko has evolved a kind of onboard parachute,
Webbed toes and flaps of skin along its sides
act like air brakes, giving it some control over its speed,
It can't travel far, but it's certainly a leap in the right direction,
But if you think the flying gecko is impressive, wait till you see its neighbour,
The draco looks like any other lizard - until it jumps,
This simple wing is actually skin membrane stretched over its ribs,
It lets this tiny lizard glide up to 100 metres,
Strictly speaking, it's still not flying,
but it saves an awful lot of climbing up and down,
One ancient reptile took gliding a stage further,
Once its arms became wings,
it could develop the power of true flight,
(SCREECHES)
And this second airborne breakthrough spawned the pterosaurs,
(MUSIC)
From fossils, we know that there were many different kinds of pterosaurs,
One had a mouth with a built-in sieve to filter out small creatures from the water -
much like a modern flamingo does,
Another had hooked teeth good for snagging slippery prey,
It used its beak to trap fish just below the surface, like a skimmer does,
Another pterosaur had an expandable throat pouch -
a built-in fishing net,
It was a kind of prehistoric pelican,
But there's one thing about the pterosaurs no bird can match - their size,
Some got as big as this!
But how did these giants get off the ground and stay airborne?
Well, John is going to show me how.
OK, John.
(JOHN) OK, let's run. (STEVE) OK.
Jumping off a cliff is a good start,
Wow! That was pretty spectacular!
Well, pterosaurs might have been slightly more graceful than that!
The largest was Quetzalcoatlus, and that got up to about 40 feet.
But how did the world's biggest ever flying animal stay up?
Pterosaurs were built very much like this - very little body and all wing.
This hang glider's made of hollow aluminium tubes,
and the pterosaurs' bones were also hollow to minimise weight.
Once up in the air, they'd have soared away and just used up draughts and thermals,
very much like what we're doing.
Whoa!
This is beautiful.
It is completely effortless -
on my part anyway!
This must be the closest thing to just growing wings and flying.
The one thing we don't really know is how these large pterosaurs landed,
but I think I'm about to find out!
By landing into the wind, we hope to avoid crash-landing,
There we go. OK.
Well, that's the theory!
(STEVE LAUGHS) Excellent! That was great!
Pterosaurs must have been a magnificent sight,
They ruled the skies for 150 million years,
but they mysteriously vanished along with the dinosaurs,
By then, a third airborne animal had arrived,
Its success was down to a brand-new structure -
one that would lead to the most beautiful flying animals the world has ever known - the feather.
(MUSIC)
The surprising thing about feathers is that they didn't even evolve for flight.
Not only that, birds didn't even invent the feather - they inherited it.
(ROARS)
Birds are directly descended from a group that includes the greatest predators of all time,
These fossils are of small meat-eating dinosaurs,
but look more closely and you'll notice some mysterious impressions made by feathers,
So what made these scaly hunters go fluffy?
Feathers are in fact modified scales,
Over countless generations, some scales began to thin and fray,
evolving into fluffy down,
but what did dinosaurs need these feathers for?
Today, fluffy feathers are still used by young birds like albatross chicks to keep warm,
In the Antarctic, they must survive sub-zero temperatures for months on end,
Downy feathers might well have helped insulate small dinosaurs,
but what they weren't much good for was making a wing,
So how did fluffy feathers like these turn into stiff ones like this used for flight?
The latest theory is that evolution hijacked the feather for a different job
long before it was used for flight. Hello.
It's now thought that feathers might have been used for display, just like many birds do today.
And stiff feathers make for far more spectacular displays than fluffy down,
Male birds flaunt themselves to win over a female,
and perhaps it was the same for dinosaurs,
By choosing the most striking males,
the females helped feathers evolve in a completely different way,
As soft feathers became longer and stronger, they were more suitable for building wings
as well as showing off,
So feathered dinosaurs weren't just the warmest, they were also the prettiest.
And they were ready to take flight,
But how did that first leap into the skies actually happen?
One theory is that feathered dinosaurs lived on the ground
and flapped their feathery arms to help them jump for insects.
But the most poplar theory,
and certainly the one I find easiest to believe, is that flight started up here, in the trees.
A set of feathered arms would come in very handy for a tree-dwelling dinosaur -
they'd break a fall, and it's easy to imagine with a few modifications,
how they cold turn leaping into gliding.
Then, as feathers and the muscles moving them continued to develop,
arms were reshaped into wings strong enough to flap their way into the air,
Gliding became true powered flight,
Enter the birds,
The evolution of birds was a massive breakthrough.
Their superb flying ability unlocked a way of life that has proved very successful.
The dinosaurs died out, yet birds survived,
and more than that, went on to dominate the skies,
(MUSIC)
All this thanks to the fabulous feather,
The arrival of the birds marked a new era in the history of life
and the beginnings of an evolutionary battle that would push flight to the extreme,
Each spring, adult mayflies have just a few short hours to get out of the water,
find a mate, breed and lay eggs,
But many never make it,
The mayfly feast lasts just a few days,
but there's lots more insect food on offer if you can get to it,
In an average summer month,
it's estimated that around four billion insects fly over each square mile of Britain,
That's around one ton of insects.
And I bet the people down there have no idea what's floating around above their heads!
We can't see them up here because they're so small,
but there are birds that can, that have evolved to reach this banquet in the skies,
And none are better at it than the swift.
It's the ultimate high flier.
Swifts spend most of their life on the wing and all because of insects,
They fly from South Africa each year for our summer's insect feast,
a return trip of around 14,000 miles,
A long history of aerial pursuit
has given swifts a streamlined body with long narrow wings to slice through the sky,
Only when filmed at normal speed
can you really appreciate how well they live up to their name,
Swifts are so specialised for living on the wing, they can't even land on the ground,
Their tiny legs and long wings would make it impossible for them to take off again,
That's why they always nest up high,
One mouthful like this contains up to 500 insects,
and when food is plentiful, the chick may get ten meals - 5,000 insects in a day,
But in bad weather, most insects are grounded, and the parents have a hard job finding food,
Sometimes, the adults have to desert their chicks and fly ahead of the storm to feed,
A British swift will even cross the sea to Europe,
A trip to Holland's no big deal when you can cover more than 180 miles in a day,
Back at the nest,
the helpless chick can only wait whilst the adults feed in fair continental skies,
Another day, and still the chick waits, living on its fat reserves,
Swift chicks are tough,
They can lose half their bodyweight, surviving for days without a meal, but there is a limit,
This chick needs to eat, and soon,
The parent is in sight of home, after a round trip of perhaps 1,000 miles or more,
It's just in time to deliver a life-saving meal,
Millions of years of chasing tiny-winged insects have shaped swifts into true aerial aces,
Amazing to think that they started as feathered dinosaurs that clambered around in the trees!
Central America is home to the swift's closest living relatives -
a group of birds that have pushed flight along a very different evolutionary track,
Hummingbirds.
Hummingbirds can fly backwards, forwards, up and down,
and all with unbelievable precision,
These aerobatics are unrivalled among birds,
And all because of flowers.
But how did flowers lead to such fancy flight?
Over millions of years, hummingbirds and plants have struck up an evolutionary deal,
The hummingbirds get to drink nectar in return for pollinating plants,
And hovering has proved the most efficient way to get a meal,
It's a relationship that's been perfected until bird and flower fit together like a key in a lock,
Plants have forced hummingbirds to become more like feathered insects,
At first glance, it's hard to tell a hummingbird from a hummingbird hawkmoth,
It's a great example of what's known as convergent evolution,
where two entirely unrelated animals find almost identical solutions to the same problem,
But the hummingbird’s supreme flying ability comes at a great cost.
Their wings flap an amazing 80 times a second,
needing flight muscles twice as big as those of other birds,
Their heart beats an astonishing 1200 times per minute -
nearly 20 times faster than yours or mine,
To fuel all that, a hummingbird eats roughly half its weight in sugar every day,
They're slaves to their own lifestyle, locked in a never-ending quest for food.
And they can only achieve such precision flying by staying very small,
Swans have the opposite problem.
They're so heavy that just getting into the air is a struggle.
Come on, then. Come on!
Come on, swans! Come on.
Come on, swans. Come on.
Come on. Up you go.
Come on, boys and girls.
Here we go.
Fantastic!
Look at that!
Hello!
Oh, yes! Look at you.
You beauties!
Swans are one of the heaviest of all flying birds.
They're like the bird equivalent of a jumbo jet, so they take a lot of energy to get into the air.
Once they're up in the air, it's all about saving energy, and that's why they fly in this formation.
By sticking close together,
each bird gains a little extra lift from turbulence created by the bird in front,
It's enough to make a 50% energy saving,
And when you’re this big, landing is also a problem.
OK, girls.
OK, here we go.
Whoa! Skids down...
Perfect.
I don't think I have ever seen anything quite as spectacular as that.
That is unbelievable.
I think you deserve a treat after that.
Easy! There we go.
Very good.
Thanks to that first feathered dinosaur,
today, more than 9,000 species of bird fill the air
across every continent,
(MUSIC)
And the eagle is the king of them all.
The ultimate symbol of power and dominance of the skies.
But like most birds, it does have a weakness - its eyes work best in daylight,
That left the night sky up for grabs,
and another family of animals seized their chance.
(CLICK)
Bats. Some of the most mysterious of all animals.
Creatures of the night that can find their way around in darkness,
and live secret lives in deep, dark places.
But perhaps their biggest secret is how they evolved.
Bats are descended from a small nocturnal mammal
that took to the trees in search of prey, like tree shrews do today,
They probably began to glide on skin flaps stretched between their limbs,
like flying squirrels and sugar gliders,
(MUSIC)
It's a great way to get around, but still not real flight -
more like free-falling with style,
But it's the colugo that may provide the missing link
to show how bats evolved true wings,
The difference is in its hands - they're webbed,
The bat's ancestor had these, too,
but its fingers got longer and the skin between them stretched to turn hands into wings,
Eventually, it flapped these wings and took off,
making bats the fourth and final group
after insects, pterosaurs and birds, to really fly,
You might think that one bat is pretty much like any other,
but they're one of the most widespread and diverse of any kind of mammal.
This one is a fit bat and, apparently, likes his banana.
Go on. Get that into you.
I think you really have bitten off more than you can chew.
Fruit bats like this flying fox are the biggest of all bats,
They have a wing span of up to five feet,
They spend the day crowded together in their favourite trees,
There can be millions in a single colony,
Then, as dusk falls, there's a mass exodus,
The power of flight means they can cover up to 30 miles a night in search of the ripest fruit,
No other mammal puts on a show quite like this,
(MUSIC)
Bats are now one of the most successful types of mammal on Earth,
There are nearly 1,000 species, each with its own special habits,
Many are fruit lovers,
Others sip nectar,
Other bats have even learned to fish,
But what most like to eat is a big fat juicy insect,
Bats need more than wings to track down food in the dark,
These creatures of the night had to evolve a new way of mapping out their world,
They listen to the echoes of their own calls and create an image of their surroundings,
(CHIRPING)
It's called echolocation, but how did such a complex system evolve?
(ECHOING CLICKING)
It's likely bats began by using simple clicking sounds
which gave them just a very rough picture of what's around,
But detecting even basic shapes is better than flying blind,
Then, by using a more complex range of sounds,
echolocation was improved,
Bats were gradually able to pick up smaller details in their surroundings,
including their prey,
(CLICKING)
Insects filled the night sky long before the bats arrived,
They were a meal waiting to happen, and the bats tucked in,
(CLICKING)
There seems to be no limit to their sensory perception,
Using its finely-tuned echolocation skills,
the Natterer's bat can even pluck a spider from its web without becoming entangled,
(CLICKING)
Once it's got its prize, the bat goes instantly into reverse,
keeping its wings clear of the sticky threads with just millimetres to spare,
The ultimate refinement of seeing with sound,
Bats were the last group of animals to get airborne,
and like all aerial creatures,
they've used their wings to reach almost every part of the globe,
Their sheer numbers are testament to the success of flight,
Being able to fly is one of evolution's greatest triumphs,
Through countless twists and turns along life's journey,
the power of flight has shaped some of the most successful animals that have ever lived,
Today's winged creatures make up around two-thirds of all the species on the planet,
And yet they're all descended from just four ancestors
who managed to grow wings and take to the air,
We humans have always dreamed of joining them, and now we can,
Well, almost!
We do need a little bit of help - from something big, noisy,
and compared to what evolution has created,
rather crude!
Next week on the “Journey of Life”,
I'm going to discover how relationships between all living things
have shaped the variety of life we see today,