- yesterday
Category
📺
TVTranscript
00:00Mid-winter, at the bottom of the world.
00:18Antarctica, the coldest place on Earth,
00:22with an air temperature of minus 50 degrees centigrade.
00:25You'd think that nothing could survive here.
00:33Yet, huddling together, somehow these emperor penguins
00:36have evolved to cope with the battle for life in the big freeze.
00:51But cold is not the penguin's biggest enemy.
00:55The leopard seal, four metres long, a super predator.
01:14No wonder everyone's reluctant to be the first to take the plunge.
01:18Penguin and seal have a relationship forged over millions of years.
01:37That of predator and prey.
01:40It's easy to see nature as red in tooth and claw,
01:54where predators dictate who lives and dies,
01:57and only the fastest and strongest survive.
02:00But the truth is, predators and prey are just part of life's story.
02:07Our world is made up of a vast network of different relationships.
02:13Animals, including us, have to find mates,
02:17look after families, and keep up with the neighbours.
02:20And all these relationships affect how we look and behave.
02:37This is the surprising story
02:39of how the relationships between all living things
02:43have shaped the whole journey of life.
02:45Life on Earth wasn't always as complicated as it is today.
03:07There was a time when there were no relationships.
03:10There was no violence, practically no competition, and no sex.
03:17Imagine that.
03:26Three billion years ago, the pinnacle of evolution
03:29was these strange lumps on the ocean floor.
03:33Stromatolites, made up of ancient algae.
03:36It might not have the ring of the age of the dinosaurs,
03:51but the age of the stromatolites was around eight times longer,
03:54and was the longest period of peace and tranquillity
03:57that life has ever known.
04:02They might not look much,
04:04but stromatolites had the power to change the world.
04:09For the first time in the history of the planet,
04:12they produced a gas called oxygen,
04:14and so totally transformed the planet's atmosphere.
04:20Not only did they generate the air we breathe,
04:23they set the scene for all life as we know it today.
04:26Because of them, a brand new type of cell evolved,
04:33perhaps the most important life has ever known.
04:39These revolutionary oxygen-fuelled cells spawned our ancestors.
04:45But they were 20 times more energetic than the older models,
04:49and some then discovered that the quickest way
04:52to get the extra energy they needed
04:53was to steal it
04:55by engulfing other cells.
05:02A new force was unleashed.
05:05The Predator.
05:06With Predator's around,
05:22you've got to be able to defend yourself.
05:26One way is to make yourself invisible.
05:29Armour's good, too.
05:39Good, solid protection.
05:43Staying alert can mean the difference between life and death.
05:46As predators find better ways to catch and kill,
06:08their prey have to improve their self-defence.
06:12The two are locked in an intense relationship,
06:15which forces both sides to change,
06:18because neither can afford to be left behind.
06:34Nature selects only the winner's genes.
06:37The losers will disappear.
06:45This arms race has helped shape the lives and bodies
06:48of just about everything alive today,
06:51and pushed some creatures to incredible extremes.
06:53This cricket might think it's on a flower,
07:12but it's actually a mantis
07:17that's evolved to look just like an orchid.
07:20Beauty turns out to be a beast.
07:22Another hunting strategies are even more bizarre.
07:39Over millennia,
07:41the snapping turtle's efforts to reel in a fish
07:43have turned its tongue into a juicy worm.
07:46But secret weapons aren't the only winning formula.
08:02Sometimes more subtle tactics may be what you need.
08:06Meet jumping spider Portia,
08:08one of the world's smallest assassins.
08:10She's hunting the much larger web spider.
08:18She might be tiny,
08:20but she has a big appetite.
08:28Her first direct approach alerts her target,
08:32who just shakes the web
08:33and forces Portia to retreat.
08:35But Portia has evolved a plan B,
08:42a manoeuvre straight out of Mission Impossible.
08:47She slowly lowers herself within striking range.
09:02The fish, leaps, bites,
09:05and leaves the poison from her tiny fangs to do the rest.
09:16This time it isn't size or secrecy that counts,
09:19but strategy.
09:21Portia may be small,
09:23but she's as deadly as they come.
09:24The relationship between hunter and hunted
09:32doesn't only shape the way that predators attack,
09:35it also drives the way that prey fight back.
09:39Sometimes it's just about using your natural assets
09:42in a different way.
09:46When a hungry raven eyes their chicks,
09:48field fairs fight dirty.
09:50They drop bombs.
09:54A dirty trick.
10:20But hey, it works.
10:21The only problem with an evolutionary arms race
10:29is that we don't see it develop.
10:31All we see is the end result.
10:38But there are rare exceptions,
10:40like the story of the passion flower.
10:43Like other prey species,
10:44they're evolving to protect themselves.
10:46But what makes them unique
10:47is that you can pretty much watch them doing it.
10:53Plants have to fight for survival too.
10:56And even these exotic passion vines have enemies.
11:07At home in tropical America,
11:09they're under constant attack
11:11from lethal predators
11:13that lurk deep in the jungle.
11:18Heliconius butterflies.
11:22The adults are harmless enough.
11:24It's what they leave behind them
11:25that's the problem.
11:28Mother butterflies lay their eggs
11:30on the passion vine's leaves.
11:35Tiny time bombs.
11:36This plant's fate is already sealed.
11:55In a few days,
11:56there will be nothing left.
11:57If a passion vine
12:07already has a batch of eggs installed,
12:09it's pointless to lay more.
12:11A sensible mother butterfly
12:13will pass it by,
12:14which gives the passion flower
12:16a chance to fight back.
12:19Today, not all the eggs
12:20are quite what they appear.
12:22Some are in fact
12:23just yellow spots
12:24grown by the passion flower itself
12:26to try and deter mother butterflies.
12:34But in this mini arms race,
12:36not all attacks are foiled.
12:42Some passion flowers
12:43haven't quite got it nailed.
12:45These little white spots
12:46on this leaf
12:47are supposed to be butterfly eggs.
12:49But as you can see,
12:50it hasn't quite put off
12:51all of the butterflies
12:52because we've got
12:54a very greedy caterpillar.
12:56So there's pressure
13:00for ever better mimics
13:01to evolve.
13:02And some are now so good,
13:04it's hard to tell
13:05which eggs are real.
13:08False.
13:10Real.
13:13Real.
13:15False.
13:16And real.
13:18Who'd have thought
13:21that the relationship
13:22between a butterfly
13:23and a vine
13:24could have produced
13:25such a sophisticated bluff?
13:29But trouble can come at you
13:30from all sides.
13:32Even when you're safe
13:33from predators,
13:35you can often have strife
13:36from your own kind.
13:38Competition.
13:38In a rainforest,
13:44of course,
13:45the plants are all
13:46after the same thing.
13:48Precious light.
13:52And they can't all be winners.
13:55Only those best adapted
13:56to compete survive.
14:01It's the same principle
14:02wherever there's a crowd.
14:03In Africa,
14:05meat is the prize.
14:11A vulture has the aerial advantage
14:13that means it can spot
14:14the first signs of a kill,
14:16but it won't have long
14:17to feed undisturbed.
14:22Before long,
14:23every vulture in the area
14:24is fighting for a beakful.
14:26At this buffet,
14:36now only the toughest
14:37get to eat.
14:40Lapet-faced vultures
14:41are the biggest
14:42bully boys of all.
14:44They knock the smaller
14:45griffins flying.
14:46But a free lunch
15:01attracts other hopefuls too.
15:04More feathers fly
15:05as even lapets
15:06have to make way
15:06for the mammal heavy mull.
15:08Like predators and prey,
15:24this kind of competition
15:25is a real force
15:26to be reckoned with.
15:28Another influence
15:29on evolution
15:30which selects only
15:31the toughest to survive.
15:38Competition is so crucial
15:40to animals' lives,
15:41it can have a massive
15:42impact on their body shape.
15:49Browsers have been
15:50moulded into different
15:51shapes and sizes
15:52so they don't tread
15:54on each other's toes.
16:02Tiny dick-dicks
16:03can nibble around
16:04the thorny lower branches
16:05in a way no bigger
16:07animals can.
16:08So they don't need
16:09to reach higher
16:09than a couple of feet.
16:16Tore impala
16:17have control
16:18over the acacia's
16:18middle zone.
16:22But even they
16:23are kept in their place
16:24by the gerinuk,
16:25which has a poise
16:26no other antelope
16:27can match.
16:33Gerinuks look more
16:35like ballet dancers
16:36than gazelles.
16:36They even balance
16:38on their points.
16:42Their specially adapted
16:43hips and spines
16:44enable them to swivel
16:46vertically
16:46and stand tip-tail
16:48on their hind legs.
16:48but there's one animal
16:56who can feed even higher
16:58still, up to six metres.
17:01It has a flexible
17:02leathery tongue
17:03which it can use
17:04like a hand
17:05to pluck the highest
17:06twigs and leaves.
17:08Thanks to evolving
17:09the longest neck
17:10in the world,
17:11the giraffe.
17:12so competition
17:27hasn't just pushed animals
17:29into developing
17:29different eating habits,
17:31it's helped create
17:32entirely different species
17:34that can live together
17:35in harmony.
17:36But what happens
17:43when neighbours
17:44want exactly
17:45the same thing?
17:48Ring-tailed lemurs
17:49live in troops
17:50on the island
17:51of Madagascar.
17:53Each group
17:54needs their own territory
17:55to survive
17:56for shelter,
17:57food
17:58and a safe place
17:59to rear their babies.
18:00but they're often
18:02under threat
18:03from other lemur gangs
18:04who'll steal
18:08the whole thing
18:09if they can.
18:22The alarm sounds.
18:24These intruders
18:25look like the mean business.
18:27Time to rally the troops.
18:30Lemur society
18:40is run by females
18:41so it's they
18:43who lead the band
18:43into the fray.
18:45Soldiers
18:46with babies
18:46on their backs.
19:00When competition
19:19gets this intense
19:20the lemur's answer
19:21is teamwork.
19:22Once animals
19:41are driven
19:41to work together
19:42the close relationships
19:44which evolve
19:45can open up
19:46a whole new way
19:47of life.
19:47meerkats are high
19:54on the menu
19:54for many predators
19:55so they need
20:00to work together
20:01to protect themselves.
20:02they're one of the few mammals
20:20that take turns
20:21at doing different jobs.
20:23while the rest
20:30of the family
20:31starts digging
20:32for breakfast
20:32one member
20:34stands guard
20:34looking out
20:35for predators.
20:40The others
20:40can carry on
20:41feeding safe
20:42in the knowledge
20:42that someone
20:43is watching
20:44their backs.
20:44and it's not
21:11just lookout duty
21:12meerkat share
21:13when a monitored
21:16lizard appears
21:17they all gang up
21:18to drive it away.
21:29En masse
21:30these little creatures
21:31make a formidable force.
21:43being such good
21:50team players
21:51is the meerkat's
21:52winning formula
21:53it's all for one
21:55and one for all
21:56it's easy to see
22:00why we'd help
22:00our own relations
22:01but some animals
22:03cooperate
22:03with different species
22:04how could that evolve?
22:08there's an answer
22:10to be found
22:11in the sea
22:11a coral reef like this
22:40is a natural metropolis
22:41where everyone
22:43is trying to get on
22:44and make their own way.
22:47it's full of opportunities
22:49deals to be struck
22:51some enterprising characters
22:54are cleaning up
22:56it turns out
22:59there's a market niche
23:00for professional groomers
23:01cleaners
23:08like this tiny wrasse
23:09snaffle up their clients
23:11parasites
23:11and dead skin
23:12they set up their own
23:15cleaning stations
23:16customers come from
23:18far and wide
23:19for dental hygiene
23:20or a gill wash
23:21in return
23:22the cleaner gets a meal
23:24cleaner shrimps
23:30cleaner shrimps too
23:31serve a most discerning
23:32clientele
23:33fish are smarter
23:42than you might think
23:43they have good memories
23:45and come back regularly
23:46to be pampered
23:47in exactly the same spot
23:48and by the same cleaner
23:50the coral crowd
23:59soon learns
23:59which are the top salons
24:00boasting the most
24:02talented staff
24:03it's not just
24:12tropical fish though
24:13who've discovered
24:14that hiring a little help
24:15can help you get ahead
24:17some plants have too
24:21this garden only exists
24:30because of an ancient
24:31alliance between insects
24:32and plants
24:33it's a real match
24:38made in heaven
24:39as it's produced
24:40some of the most beautiful
24:41of all living things
24:42flowers
24:44since flowers
24:52can't move around
24:53they need help
24:54to carry pollen
24:55between them
24:56so they can produce
24:57fertile seeds
24:58so they advertise
25:03themselves
25:03as nectar feeding stations
25:05as the insects feed
25:16they get an extra
25:17takeaway of pollen
25:18it's an even-lutionary
25:21partnership
25:22that has proved
25:23so successful
25:24flowering plants
25:25now dominate our world
25:27to guarantee delivery
25:38some flowers have developed
25:39an exclusive contract
25:41with their pollinators
25:42orchids
25:44the royal family of flowers
25:46can be very demanding
25:47indeed
25:48some like this bucket orchid
25:53seem downright cruel
25:55this euglossine bee
25:59has to visit the bucket orchid
26:00he needs its perfumed oils
26:02to use as an insect aftershave
26:04to attract a mate
26:05but as he gathers the oil
26:10he loses his grip
26:12exactly what the orchid wants
26:16it has evolved a complex trap
26:21which press gangs
26:22male bees into service
26:23the only way out
26:26is via the back door
26:27and the orchid's pollen sacks
26:29the pollen sticks
26:52to the delivery bee's back
26:54once free
27:00he takes a short while
27:01to dry off
27:01surely he'll never go near
27:08a bucket orchid again
27:10but either male bees
27:12have short memories
27:13or run out of aftershave
27:15because here he is
27:16falling for the same ploy
27:17all over again
27:18the only difference this time
27:24is that he's delivering pollen instead
27:26no question who's wearing the trousers
27:31in this relationship
27:32although the bond between flowers and insects
27:41has extraordinarily beautiful results
27:43plants also depend on an invisible partnership
27:47which is even more important
27:49because without it
27:51most of them wouldn't even exist at all
27:53they need it to grow
27:55and some plants
27:56like these guys here
27:58grow very big indeed
28:00Californian redwoods
28:05are the tallest trees in the world
28:07they can live for more than 2,000 years
28:10and grow more than 300 feet tall
28:13these giants might be some of the largest
28:15of all living things
28:17but they rely on the tiniest of partners
28:19partners so small
28:21that they're almost invisible
28:22and if I'm to stand a chance
28:24of getting to see them at all
28:25I've got to go all the way
28:27back down there
28:28they're microscopic
28:41and they live hidden underground
28:43amongst the tree's roots
28:45these secret partners turn out to be fungi
29:03they penetrate the tree's roots
29:05then stretch out through the soil
29:07as a network of tiny threads
29:09the giant trees can't get enough water
29:13and nutrients on their own
29:15but the fungal network can
29:17its massive surface area
29:20sucks up the fluid and minerals
29:21the trees need
29:22and then transports them
29:24back up to their roots
29:25and what do the trees do
29:29for the fungi in return
29:31just feed them sugars from their leaves
29:33not a bad deal
29:3490% of all plants live with fungal partners
29:40from the redwoods to the rainforests
29:43it's a 400 million year old marriage
29:46it's possible that without it
29:49plants might never have been able to colonise the land
29:52and without all this green stuff
29:56where would all we animals be?
30:04but the close relationship between plants and fungi
30:08is just one of the great alliances that have shaped life
30:11there's another
30:13you'd need a microscope to see it
30:15but it is perhaps the most important partnership on earth
30:18it provides the power for nearly all living things
30:22driving every cell in our bodies
30:24and it's what gives animals their energy
30:38scattered through the cells of all our bodies
31:07these are billions of mysterious structures
31:10called mitochondria
31:11each is a tiny furnace that releases energy from our food
31:16and generates the life force that our bodies need
31:20animals like me
31:28and all these guys
31:30can only exist because of the energy the mitochondria release
31:33it's a crucial relationship
31:37and one with very unusual beginnings
31:39in fact it didn't even start as a partnership
31:42come on then big man
31:44billions of years ago
31:50the mitochondria lived independent lives
31:52as free-floating bacteria
31:54but our ancestor cell changed all that
31:57it engulfed one
31:59but instead of eating it
32:01our ancestor formed an alliance with its prey
32:06the two joined forces and were transformed
32:14the bacteria became a mitochondrion
32:16and together they created a new type of hybrid supercell
32:20a supercell which was the basic building block for almost everything alive today
32:27so could this mean that it is cooperation and not conflict
32:32which is actually the strongest force in evolution
32:35is the fight for life more the embrace of life
32:40it's a lovely idea
32:42but relationships
33:11relationships
33:12they're never straightforward are they
33:16most grazing animals in Africa
33:18are plagued by biting insects and ticks
33:21they also have what seem to be whole squads of helpful hangers-on
33:27what can they do
33:34oxpeckers
33:35insect-eating birds who reach the parts the animals themselves can't
33:40but oxpeckers aren't quite as innocent as they appear
33:47they don't just eat up ticks
33:50They don't just eat up ticks, they peck holes in the animal's skin.
33:59What appear to be honest little helpers, in fact, turn out to be blood-sucking parasites.
34:08A way of life which, rather horrifyingly, is far more common than you might expect.
34:18Over half of all creatures alive today are parasites, an insidious hidden force that
34:33has infiltrated just about every other living thing.
34:43The Natural History Museum in London has one of the largest collections of biological
34:47specimens in the world, including some particularly gruesome parasites, all now thankfully pickled
34:57in alcohol.
35:04Having a relationship with a parasite is very much a one-sided affair.
35:10This might look like pasta, but it is in fact a tapeworm from a killer whale.
35:15Its natural home is inside the intestine of the whale, robbing it of its food.
35:21They can grow to 60 feet in length.
35:25Imagine that inside your gut.
35:31Which is perfectly possible.
35:33This tapeworm can take up residence in humans too.
35:43This is a human botfly larvae.
35:46It's smaller than the tapeworm, but it's much more gruesome.
35:49It burrows into the living flesh of people.
35:52Victims of this parasite have reported that they can hear it munching away in their skin.
35:57And this one had to be surgically removed from someone's head.
36:00If you're going to pick a parasite to play host to, this is not the one to choose.
36:10But parasites aren't just gruesome.
36:13Because they affect virtually every plant and animal alive, they may just be the biggest
36:18influence on the whole of evolution.
36:24Can that really be true?
36:29Well, take rabbits for example.
36:34You might expect predators to be the biggest influence on their lives.
36:41After all, they're hunted by a whole army of killers.
36:44But with predators, they can at least run away.
36:55Rabbits face another threat, which they can't see, smell or hear.
37:03Each rabbit is infested with thousands of fleas, ticks and minuscule mites.
37:09Which may be small, but pack a powerful bite.
37:14These tiny bloodsuckers sap the rabbit's strength.
37:17But within them, they carry an even deadlier threat.
37:22These little wild baby rabbits have been abandoned by their mother.
37:26But they've been very fortunate because they've been adopted by a human.
37:31Not only has this meant that they've escaped predation, but they've also been saved from
37:35the biggest rabbit killer, the myxomatosis virus.
37:44A virus is a nightmare straight out of a science fiction movie.
37:50It's an invader with one aim, to replicate.
37:53It contains special components which enable it to fulfill its mission.
38:04A potential victim, the outer surface of a body cell.
38:09On first contact, the virus docks and merges with the cell membrane.
38:20Its inner pod enters the cell, seeks out the command center, the nucleus, and then injects
38:26its secret weapon, a snake of virus genes.
38:31These then corrupt the cell, making it into a virus factory.
38:39Eventually the cell dies and bursts, releasing thousands of new viruses, and the real destruction
38:45begins.
38:49Each year, just about every baby rabbit born in the wild will catch this deadly virus.
38:54Typically it kills four out of five.
38:58That means in a litter like this, only one would survive.
39:10Viruses are a truly fearsome evolutionary selection force, far more deadly than predators or competition.
39:28Every living thing has to evolve to fight off viruses, or risk extinction.
39:39I'm talking about warfare on a cellular level, which affects all species alive, including us.
39:47In 1918, at the end of the Great War, a flu virus struck Europe.
39:53The war killed 25 million people over four years.
39:57That's three times the population of London.
39:59But the flu epidemic wiped out the same number in just four months.
40:08A virus can wipe out a population, and can even threaten an entire species.
40:27So against such a powerful enemy, how can anything possibly fight back?
40:35Well the answer just happens to be a major obsession for a good many species on this planet, including
40:40ourselves.
40:41It's sex.
40:42How can sexual relationships have anything to do with the fight against parasites?
41:09Surely sex is just a matter of reproduction?
41:18You'd be surprised.
41:20It turns out there's a lot more to sex than just making babies.
41:24There are lots of living things that reproduce without it, by cloning.
41:28Look at this spider plant.
41:31It's grown all these babies here, just ready to drop off and start growing.
41:35They're perfect little mini versions of the mother plant.
41:38No need for sex at all.
41:41And it's such a neat trick that many animals do it too.
41:45Aphids are baby machines.
41:51They don't need to have sex with a mate, because they can pump out new aphids all by themselves.
41:56One every 20 minutes, each already full of their own future daughters.
42:07Cloning is great for increasing numbers, but it has one flaw.
42:11As all cloned babies are identical, a single killer bug could wipe them all out.
42:24The key thing sex does is create variety.
42:27It's like me and you.
42:28We're both basically the same, but we are subtly different.
42:32We're individuals.
42:38It's a pattern that's repeated for all kinds of different animals, from people to puppies.
42:43Like these little bull terrier puppies.
42:46Ah, yes!
42:48Even within one mating, you get incredible diversity, as you can see in this litter.
42:54They all have the same mum and dad, so how come they're so different?
42:59It's all to do with the secret magic of sex.
43:04During sexual reproduction, the genetic material is reshuffled.
43:09Every sperm and egg is unique.
43:11So when the two join together to make a puppy, every puppy is born unique too.
43:18They all look different, but what's critical in the fight against parasites are the differences
43:23you can't see.
43:25These puppies' bodies are unique on the inside too.
43:31This one might be more resistant to parvovirus than the rest of them.
43:37And this one might be more resistant to distempervirus.
43:43And it's the same for you and me, with human diseases too.
43:52Different individuals have cell membranes which lock the killer virus out.
43:56So its lethal life cycle can't get started.
44:05This is why sex is so crucial.
44:07Because we're all born so different, we each present a different challenge to the parasites,
44:12increasing our chances of survival.
44:14It's like genetic roulette, with every new generation keeping the killer bugs guessing.
44:21No wonder animals are so desperate to have sex.
44:24It's evolution's way of future-proofing new generations.
44:35But to have sex, you do need a relationship, however brief.
44:40And many animals go to a lot of trouble to make sure they find a mate.
44:52This element of choice means sexual relationships can have a huge effect on animal evolution too.
45:02Once a year in autumn, American elk gather together to breed.
45:10It's called the rut, a spectacle where stags compete for breeding rights.
45:24This rut is played out in a most unusual location.
45:32In the mammoth area of Yellowstone National Park, manicured lawns like this attract the
45:37herds in.
45:38Right into the centre of Yellowstone village itself.
45:43Here humans get a ringside seat.
46:01Each stag has two aims.
46:04To impress the females, and to frighten off rivals.
46:10Although the males are much bigger and more dominant, it's the females who really run
46:14this show.
46:16Like females the world over, they'll be left holding the babies, so they're very choosy
46:21about who they mate with.
46:30Only the real studs, with the most impressive antlers and fighting ability will do.
46:36Which forces the males to prove themselves.
46:40It's a knockout contest, where only the winners get the right to breed.
46:53So over generations, the battles get harder and the stags stronger.
46:59Female choice means that sexual relationships can shape the bodies and behaviour of their
47:04mates, so they are driving evolution.
47:08The males get so charged up when they're fighting over females, that they'll perceive just about
47:12anything as a threat.
47:19The overwhelming urge to win and pass on their genes can push the stags right over the edge.
47:33The
48:02Thankfully for us males, there are other, less violent ways of courting favour.
48:09Sometimes it's all just a matter of appearances.
48:15One doesn't always have to fight to prove one's worth.
48:19Often it's a matter of showing off.
48:23So some males put all their effort into how they look.
48:30Posers can be just as successful as fighters.
48:43Instead of proving their worth on the battleground, these peacock males flaunt fancy dress instead.
49:00The females will only mate with the ones they find the most attractive.
49:15But does all this ostentation and display actually mean anything?
49:23How can a female be sure she's going to have good, strong, healthy babies?
49:28Are good looks all they're cracked up to be?
49:38Remarkably, a little finch proves that masculine beauty is not just skin deep.
49:43Zebra finch males are very colourful, with orange legs and cheeks and bright red beaks.
49:56The females are much plainer.
50:00So why are the males so colourful?
50:06Let's try a little experiment.
50:09The males' red legs and beaks are full of colour pigments called carotenoids,
50:15found naturally in fruits, seeds and carrots.
50:19So here I'm going to feed half the males a diet high in carotenoids to make them redder.
50:38And then put them in a special choice chamber next to a duller male who hasn't been fed the pigments.
50:47Two males in their own designer bedrooms at the back, one female at the front.
50:56The sexes are segregated by a pane of glass.
50:59The males can't leave their rooms, but the female at the front can move from one side to the other.
51:04She can choose a male by perching by his window, either on the left or on the right.
51:12And tiny cameras are installed to record what happens throughout the little birdhouse.
51:21This high-speed CCTV footage shows what happens next.
51:26Watch the female at the bottom of the screen.
51:29She seems to have chosen the male on the left.
51:35And the camera in his bedroom shows she spends most of her time with him.
51:42While another camera reveals the other guy is ignored.
51:45And who do you think is the most popular?
51:50The male with the redder beak.
51:52In fact, in these tests, nine out of ten females preferred him.
51:59But why would they fancy the most colourful male?
52:03Well, the same red pigments not only make the male look good, they help his body fight diseases too.
52:21A dull male is probably weaker and not a good bet as a mate.
52:25Bright colours are an honest indicator of health.
52:31So pretty males do turn out to be a good choice as mates, after all.
52:38So the next time your mother says, eat up your vegetables, you know it's a good idea to listen to her.
52:43Especially if you're male.
52:49A brightly coloured male is not just likely to be healthy, he'll also pass on his parasite-fighting genes to his babies.
52:58So it pays for a girl to demand the best.
53:14And this male zebra finch has passed his medical with flying colours.
53:21But there's an extra twist.
53:23Researchers now think that girl power can even create new species.
53:26But how?
53:30Well, this guy can give us a clue.
53:33He's a zebra cichlid.
53:35And experiments have shown he's a totally dedicated follower of fashion.
53:42These fish are only found in Lake Malawi in Africa.
53:48What makes them special is that males come in a variety of technicolour coats,
53:52which is extremely unusual in a single species.
54:00It was a mystery as to why the males came in so many different colours.
54:05They certainly weren't evolving to hide from predators, or adapting to local conditions.
54:10Something else was going on.
54:14And that something was the females.
54:19To find out more, we put the fish in choice chambers.
54:23The larger, more colourful males are confined, but the little brown females can swim where they like.
54:33All they have to do is swim in with the male they fancy most, and their choice is made.
54:38The tests have produced some rather surprising results.
54:45It turns out even females of the same species have different ideas about what is sexy.
54:52Some prefer white males, some yellow, others blotchy, and so on.
55:03Which explains why zebras cichlid males come in so many different colours.
55:09But how does that help to create new cichlid species?
55:13Well, this is where the girl power bit kicks in.
55:18If a group of females gang together and decide that one colour is now highly desirable,
55:24they'll only mate with those particular males.
55:27This preference is passed on to their daughters.
55:30Over generations an entirely separate breeding group is formed,
55:34and eventually a new type of cichlid.
55:36Girl power not only helps to create beauty, it also leads to amazing variety,
55:52and ultimately new species.
55:54Lake Malawi and the other African Great Lakes started out with just a handful of cichlid species.
56:17Now they're home to one in ten of all kinds of freshwater fish on the planet.
56:22An incredible 1,700 cichlid species, all fashioned by female choice.
56:33This is the greatest explosion of new species ever discovered,
56:38all driven by the relationship between females and their males.
56:43The truth is, of course, that sexual relationships are only one of the many interactions between living things
56:50that have the potential to shape and drive life.
56:54Whether with families and friends, competitors or enemies, living together isn't always easy.
56:55But relationships have been a massive force for change.
56:57Throughout the whole journey of life.
56:58It's been a massive force for change.
56:59Throughout the whole journey of life.
57:00It's been a massive force for a change.
57:01Whether with families and friends, competitors or enemies, living together isn't always
57:16easy. But relationships have been a massive force for change throughout the whole journey
57:25of life. And ultimately, it's our connections with each other that have created the spectacular
57:33variety of life we see today.
57:55Next week on the journey of life, I'm going to retrace our five million year journey from
58:19ape to human and discover how we very nearly didn't make it.
58:24Music
58:29.
58:31.
58:32.
58:36.
58:36.
58:38.
58:50.
Recommended
57:59
|
Up next
58:00
58:55
58:54
7:08
49:05
58:34
4:48
1:50
58:38
29:15
37:53
28:41
1:49:30
49:16
29:04
43:33
1:49:07
38:55