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00:00Life is full of beauty and drama, and its driving force is sex.
00:24Every animal on earth is descended from a 4 billion year dynasty of successful breeders.
00:41We now know that the urge to breed is driven by genes which compel animals to fight and even die for sex.
00:54The evolution of sex has been the greatest breakthrough in the history of life.
01:00It's a battleground where only the sexiest will triumph.
01:07We're going to need a new hero.
01:21Sir.
01:23Many of nature's bloodiest battles are fought for the sake of sin.
01:53It's easy to take such passion for granted, but why should males and females suffer so much for sex?
02:06The real payoff lies not in the act itself, but in continuing their family line.
02:20Sex is life's gateway to the future, a way for genes to pass from one generation to the next.
02:29And genes drive both males and females to behave in extraordinary ways in the quest for immortality.
02:39For animals, that vital quest can be life's ultimate challenge.
02:56The struggle to breed makes heavy demands. One sex often pays a higher price than the other.
03:03Many females are burdened with bringing up babies, while for most males the only chore seems to be sex itself.
03:22Except for sex, it often seems that females could raise families on their own.
03:41Even when it comes to hunting, it's often the females that do all the work and take the greatest risks.
03:53Take the greatest risks.
04:23Death or attack once in a year's field, it's possible to be a very honest killer with the species.
04:46Don't help with me.
04:48Even when caught, prey can still injure the hunters.
05:08Despite all this effort, the lionesses don't have long to enjoy their spoils.
05:13The bigger, stronger male soon claims the lion's share.
05:43Many females seem to get a bad deal out of life for the sake of sex.
05:53But they are simply being driven by their genes.
05:57The females instinctively make sacrifices in order to breed.
06:01Throughout the animal world, equality rarely has a place in sex.
06:14But just occasionally, it's the male, not the female, that makes the ultimate sacrifice.
06:20A male, red-backed spider has found a female's lair.
06:27But will he be recognized as a potential suitor?
06:30Or will this female see him as her next meal?
06:49Will this female see him as her next meal?
06:53His footsteps vibrate the web, sending all the right signals.
06:58She gets the message and stays still.
07:04Tentatively, he maneuvers into place.
07:07One false move, and he could be dead.
07:10His palps, resembling tiny boxing gloves, are packed with sperm.
07:22He drums them against her as the prelude to an extraordinary sexual act.
07:28He's in, and the sperm transfer begins.
07:34But at this climactic moment, he makes a bizarre move.
07:40He flips his body over into her jaws.
07:45He forfeits his own life, all for the sake of sex.
07:52But there's method in his madness.
07:55While she's busy eating, he's still pumping.
07:58And more sperm means more of his babies.
08:04For his genes, it makes perfect sense.
08:10He has to die sometime, and by trading in his life early,
08:15he's ensuring a bigger stake in the next generation.
08:21Such suicidal strategies have evolved surprisingly often in the mating game.
08:27In this river, sockeye salmon are reaching the end of their lives.
08:39The past few weeks have taken their toll.
08:49They've swum 1,500 miles upstream from the ocean in search of sex,
08:55driven by instinct to push on and on.
08:59It's the journey of a lifetime.
09:01The past few weeks have been moving in to the sea.
09:03The past few weeks have been on and on a plane.
09:04The past few weeks have been on and on a plane.
09:05It comes out to the ocean, and on a plane.
09:06But it's the time to push on and on the ground.
09:21It's the time to the sea.
09:23It's time to push on and on.
09:23And on and on.
09:25They've made it to the gravel bed where they first hatched.
09:38Exhausted by their struggle, they have one last mission.
09:42They must compete for mates.
09:47Males jostle one another for a chance to fertilize a female's eggs.
09:55The stakes are high.
10:14Those that breed are winners in the evolutionary war.
10:19Those that don't are destined to evolutionary oblivion.
10:25Every salmon will die, but some will live on through their offspring.
10:37Within each egg lie the blueprints of life, genes inherited from both parents.
10:46Instructed by those genes, a shapeless egg turns into a baby salmon.
10:52A salmon with a genetic pedigree to breed successfully.
10:57The secrets of success are passed down countless generations within genes that approach immortality.
11:08The individuals that carry them live only a few years.
11:15But there are far easier ways to pass on genes without the sacrifices of sex.
11:22Remarkably, these sea anemones can reproduce without a partner.
11:36They don't need sex.
11:55The anemones simply split themselves down the middle to create two identical animals, clones.
12:14It seems drastic, but it's a very effective way to breed.
12:18No need to search for a mate.
12:20No risk of being exploited by one.
12:23And it's quick.
12:24In just a few hours, one anemone divides into babies that can reproduce in exactly the same way.
12:31The young anemone is a perfect clone of its parent, sharing identical genes.
12:56And cloning as a means of rapid reproduction is a method used by more complex animals, too.
13:07In the wake of a tropical cyclone, a raft of vegetation drifts in the ocean.
13:15On board is a small passenger, a female gecko.
13:25The raft runs aground on a remote island.
13:29It's a safe haven, but there are no other geckos here.
13:33So there's no chance of her finding a mate.
13:38But this gecko is no average castaway.
13:45For her, isolation isn't a problem. It's an opportunity.
13:52She's fully equipped to reproduce alone.
13:58And once in the shady interior of the island, she will waste no time in starting her own colony.
14:08She lays eggs. But she does not need a male to fertilize them.
14:13Inside each, an embryo will develop identical to its mother. A perfect clone.
14:20A few weeks later, the baby geckos hatch. They're all female and can also lay eggs without needing to mate.
14:37Soon, the island will be crawling with geckos, all descended from the single mother.
14:43In this species, there are no males.
14:50Breeding without sex might work well on a paradise island.
14:55But it's a perilous strategy elsewhere in the world, where predators and disease are rampant.
15:01In the Australian outback, cloned geckos have a much tougher time.
15:08They must keep an eye open for danger.
15:12This gowana is just one of the predators to avoid.
15:18And there are other threats that are much harder to hide from.
15:41Tiny, parasitic mites around the gecko's eye suck her blood. Unseen diseases can also kill.
15:48And if one gecko falls ill, the whole population of identical clones is at risk.
15:58Like their island relatives, these geckos multiply rapidly. Each gives birth alone to female clones.
16:06But here, cloning is a double-edged sword. If a parasite finds a weakness in one gecko, it can infect all the others.
16:22The population can crash even faster than it grew.
16:27But living alongside the clones are other female geckos, which do pair with males and multiply through sex.
16:43It's half as quick. Males don't have babies.
16:47But sex has a distinct advantage.
16:50It mixes genes and creates unique offspring, each with its own unique defense against infection.
16:58Parasites have a tough time spreading through this population.
17:02These geckos, by shuffling their genes during sex, stay one step ahead.
17:12This key advantage helps explain why sex is so widespread.
17:17To be
17:34development, Peter literally takes the womb.
17:35Where do you figure you can understand things that matter?
17:38zweiten
17:42But the advantages of sex may reach deeper than merely shuffling the pack of genes.
17:58Sex revitalizes the genes themselves.
18:09The two sets of genes that come together during sex each have their own imperfections because
18:15genes get damaged from time to time.
18:21Sex repairs these faulty genes by replacing them with good copies from the other partner.
18:34So with each passing generation, sex rejuvenates genes, handing them the key to immortality.
18:49Throughout its two billion year history, sex has been swapping genes.
18:58The new combinations that result are the raw material that feeds evolution.
19:05Through sex, evolution has created our planet's amazing diversity of life.
19:17To breed, sexual animals must swap genes.
19:30And in the mating game, the challenge is to find the best.
19:48This is how albatross do it.
19:54After spending months apart, alone at sea, the birds are compelled by their sexual urge to
20:00spend hour after hour in an elegant dance.
20:11This is no frivolous flirtation.
20:14They're picking partners to share their investment in the future.
20:27Inside the female, this investment has already begun.
20:31The male is carrying a single large egg, an expensive life support system for the next generation.
20:42But a male produces millions of sperm.
20:47Tiny inexpensive packages of genes, a difference in size almost as old as sex itself.
20:59Two billion years ago, when it first evolved, sex was a simple matter.
21:07Cells just bumped into each other.
21:14And then swapped genes.
21:25But for an average cell living in a big ocean, this wasn't always easy.
21:32Smaller, more agile cells were better at finding partners.
21:44And larger, fatter cells, well-stocked with energy, were more easily found.
21:53Combining their talents, these odd couples paired off faster than the rest.
22:00Soon, the seas were filled with cells specialized for sex.
22:07Large eggs and tiny sperm were here to stay.
22:12Today, the difference in size between eggs and sperm has reached amazing extremes.
22:29From the outside, this female kiwi looks almost identical to her male partner.
22:36But look inside her, and there's a truly enormous egg, so large that she'll only produce a few in her lifetime.
22:52The male, in contrast, produces millions of sperm every time he mates, enough to fertilize every female kiwi on the planet.
23:03Quantity versus quality. Male versus female.
23:08Each sex has its own rules in this game.
23:13Even those curious creatures that play on both sides.
23:19On Australia's Great Barrier Reef, some animals are both male and female.
23:25Hermaphrodites.
23:28These flatworms produce both eggs and sperm.
23:32But they don't fertilize themselves.
23:35They need new genes to mix with their own.
23:38So they must cruise the reef in search of sex.
23:42When they meet, an expected move might be for one to play male and the other female.
24:01But flatworms have their own game plan.
24:04Each tries to be male.
24:06Stabbing at the other with a harpoon-like penis that can pierce any part of the other worm's skin.
24:11In this strange duel, the rules of engagement are simple.
24:25Stab and avoid being stabbed.
24:30These flatworms even have a double harpoon.
24:36Perhaps twice as effective.
24:39And all the better to inject their sperm into as many other worms as possible.
24:44Their sperm are small and cheap.
24:48And they've plenty to spare.
24:50But they keep their large valuable eggs in reserve.
24:54In every contest, there has to be a loser.
24:59But there's triumph in this defeat.
25:02The loser's eggs will be fertilized by sperm with winning genes.
25:06An asset to the next generation.
25:09For male animals, spreading their genes is cheap and relatively easy.
25:22The hardest task for some is finding females.
25:28Especially when they live in the vast tangled swamps of Venezuela.
25:37Here, all eyes are on the lookout for a dangerous, predatory female.
25:43Here, all eyes are on the lookout for a dangerous, predatory female.
25:46She's an anaconda, the swamp's largest hunter.
25:55She would have no problem eating a caiman or a capybara.
26:02She's 18 feet long and weighs more than 200 pounds.
26:08The larger she is, the more young she can have.
26:14Her fertile body acts like a beacon to male anacondas.
26:21She needs make no effort to find them.
26:30The male, only one-fifth her weight, is puny by comparison.
26:36But like the sperm he carries, he's sleek and mobile.
26:40And his all-important task is finding her.
26:51He's tracked her down.
27:02But he's not the first.
27:04Eight male anacondas are already wrapped around the female.
27:10They may remain entwined for a month or more.
27:15Each male has a pair of spurs for tickling the female, stimulating her to mate.
27:28The males wrestle to be the winner in this serpentine battle for sex.
27:36The struggle becomes clearer when the action is speeded up.
27:43The big female seems passive, but she's hugely attractive and need do little else.
28:06While the males compete among themselves, she saves her energy to nurture her eggs.
28:12But not all females are as languid as the anaconda.
28:22Sharp-eyed and on the lookout for males, female marine iguanas are waiting for their chance.
28:29They pick males based on their territories, so the larger males must compete for the best spots.
28:37Until clear winners have emerged, eating, not mating, is the female's priority.
28:47Now's the best time when the tide's out, so they race for the shore.
29:02For males seeking sex, food is off the agenda.
29:09They must stay and fight.
29:15These often bloody battles sort out the men from the boys.
29:20Important if the females are to know who's who.
29:27The females, meanwhile, gorge on fresh seaweed.
29:31Food is vital to nourish the eggs growing inside them, no matter how hard it is to reach.
29:37The battles on the rocks continue through the heat of the day.
29:56The winner will take center stage, ready for the females' return.
30:14As the females travel up the beach, they are watched by smaller males without the strength to win fights.
30:21Their tactic is to jump on passing females.
30:24But she wants a male that has fought to prove his strength.
30:42She continues on towards the rocks.
30:49A winning male welcomes females onto his patch.
30:53He sniffs them to see if they're ready to mate and to accept his genes.
30:58But still, the males must wait until the females accept them.
31:14Female iguanas pick their partners from a crowd of males.
31:21But how do other female animals choose the best when they only meet one male at a time?
31:34A surprising answer has been found in the woods of Ohio.
31:39In spring, wolf spiders start looking for mates.
31:50The female stays hidden, wary of predators.
31:57But she leaves a trail of silk that a male might find.
32:02When he stumbles on it, he detects the presence of a potential mate.
32:22She senses his tapping signal.
32:27Then sees his waving legs.
32:36But why does she choose this male above all others?
32:52The female spider's eye.
32:55Something about him really attracts her.
32:58He has long bristles on his front legs.
33:01Tufts that seem to serve no practical purpose.
33:04He shows them off by giving her a wave.
33:11But could it really be hairy legs that catch a female spider's eye?
33:15To find out, spiders' viewing habits have been analyzed.
33:22This is video dating, spider style.
33:25A mini TV screen plays life-size images of courting males.
33:30But there's something missing.
33:32This male has no hair tufts on his legs.
33:36The female is unimpressed.
33:43But show her a male with normal leg tufts, and she's interested.
33:50And if he has huge leg tufts, then she's really excited.
33:58If females find hairy legs sexy, so will their daughters.
34:02And they'll have sons with hairy legs, too.
34:05For these spiders, hairy legs are here to stay.
34:12Battles between males using good looks to attract choosy mates
34:15have led to extremes of flamboyance, especially among birds.
34:32These birds put a surprising value on their gaudy appearance,
34:51even at the risk of catching a predator's eye.
35:02But there may well be sense in a female's choice of flashy plumage.
35:15Complex patterns can be easily damaged.
35:21So peacocks with perfect plumage are probably in better condition than most.
35:27Pea-hens are known to lay more eggs for peacocks with splendidly symmetrical tails.
35:44There can also be a hidden message behind a male's showy colors.
35:50Sometimes bright colors hint at a good diet.
35:57Male house finches are colored red by chemicals in the fruit and seeds they eat.
36:05This female wants a male that's good at finding food.
36:10Red feathers suggest just that, while pale feathers could be due to poor foraging.
36:19Bright males are advertising their feeding skills.
36:22They're the ones that she'll prefer as a partner.
36:34In the weeks to come, the bright males that are good providers will make good fathers.
36:40But that's not the whole story.
36:50By choosing a bright male, the female is also choosing a healthy partner.
36:55Bright males have very few fleas and lice among their feathers.
36:59Duller males often have more, which might infest the nest and chicks.
37:05The bright males are the best choice.
37:09They're well-fed and parasite-free, literally flushed with health.
37:14Across the bird world, females carefully choose the best males they can find.
37:24But for some females, the search doesn't end, even when they've found a mate.
37:35Blue-footed boobies live in densely packed colonies.
37:43Each of these birds appears to remain faithful to one partner for life.
37:47But love thy neighbour is closer to the truth.
37:59The female has a partner she can depend on to feed her chicks.
38:04But when he's away, she's not averse to her new romance.
38:23Now the female is home alone. Male neighbours are eager to step in.
38:28While her mate's away, she's free to play the field.
38:40For her, infidelity makes sense.
38:43She already has a committed partner, but he may not have the best genes.
38:49Another male, like this one, might have more to offer.
38:58She obviously likes the look of him.
39:20And he responds.
39:25A brief courtship heads towards an inevitable end.
39:31Like all males, he's just trying to spread his genes far and wide.
39:35And the real bonus of this affair is that he won't have to bring up the chicks.
39:39Meanwhile, her regular partner goes on fishing.
39:44Meanwhile, her regular partner goes on fishing in blissful ignorance.
40:14But on his return, he soon reclaims his partner.
40:28It's to his advantage to do so.
40:31In a world full of infidelity, his repeated mating will keep his sperm in the race to fertilize
40:37her eggs.
40:42Such competition often breeds dirty tricks.
40:52And to further his own cause, a male can use all manner of cunning ploys.
41:03It's a cherry blossom time in Japan, the mating season for many animals.
41:13But these squirrels breed all year.
41:17Their liaisons are extremely brief encounters in which males use devious tactics to succeed.
41:23Males are far from faithful.
41:29They'll mate with any females they can attract using special calls.
41:33Alerted by the noise, other males join the chase.
41:50But the commotion also draws unwelcome attention.
42:01Seeing the kite, a male squirrel calls in alarm.
42:06Other squirrels hearing this sit very still, especially those out in the open.
42:14They wait for the danger to pass.
42:16They wait for the same time.
42:25Safe once more, the squirrels relax.
42:27And their mating game can begin again.
42:33There's another warning call.
42:43And sure enough, the squirrels all freeze in their tracks.
42:48All except one, the squirrel that raised the alarm.
42:53The squirrel's call was a hoax.
42:56While the other males freeze, he can go on mating.
42:59His trick has bought him time.
43:07Until the others believe the danger has passed.
43:14In the mountain meadows of Poland lives a male creature that does more than cheat a few rivals.
43:20He's an apollo butterfly.
43:25Males appear before the females,
43:31ready to mate quickly when the time comes.
43:37Down below, a female is about to emerge from this pupa.
43:43She'll be mated only once, by a fast-acting male that can beat the competition.
43:57As soon as she emerges, something about her, probably her scent, alerts males to her presence.
44:12And the race to find this virgin prize is on.
44:16Even before her maiden flight, she's discovered by this male.
44:38But how can he make sure that he's the only mate she will ever have?
44:49She receives his sperm.
45:04The mating is successful.
45:06And now he fits her with the insect equivalent of a chastity belt,
45:10to be certain that his will be the only winning genes.
45:22He leaves victorious.
45:26No other male can mate with her because he has sealed off all access
45:30with an impenetrable spiked plug that has now set hard.
45:37The female had little choice in this mating game.
45:41But sometimes, females have surprising influence,
45:44despite the physical power of males.
45:49This harem of female elephant seals has been won by a single male.
46:01And it would seem that females have no choice in the matter.
46:17But the female's discriminating tastes will soon be revealed by a sly visitor to the harem.
46:27Sneaking in from the sea, a young Casanova is looking for an opportunity.
46:42He's intent on seduction.
47:00But the females raise objection to his advances.
47:10The beach master awaits.
47:35He soon chases off the upstart bachelor.
47:39Now he stoke it in the field of movers.
47:42He is trying to stay as a giant.
47:44Clearly, the biggest is best.
48:00But the sneak was really put back where he belongs by the female's protests.
48:08These females won't settle for second best.
48:15The harem master is dominant,
48:17but not without a little help from those he seems to exploit.
48:21These females are willing concubines.
48:26Female lions, too,
48:29are willing subjects of powerful males.
48:33Females do the hunting,
48:36but males are strong defenders from other lions.
48:41When the males in a pride die,
48:44the females and cubs are left extremely vulnerable.
48:48The males in a pride die,
48:51the females and cubs are left extremely vulnerable.
49:03There are always rogue males on the prowl,
49:06ready to take control.
49:16It is a harsh rule of this mating game
49:19that an invading male will kill any cubs he finds.
49:24They can pet
49:38It's impossible to find any members at the tree.
49:46If a man wassqueakened out there were steps.
49:49If there are a few others,
49:50they don't see any other powers that have had.
49:52Oh, my God.
50:22The death of the cubs may seem brutal, but it was no senseless killing.
50:48The new male makes sure that he won't be wasting his time protecting cubs that aren't his own.
50:59The female will soon bear his young, so he'll stick around to protect them from other marauding males.
51:05In doing so, he also protects the females' new investment.
51:12This savage story shows that despite their conflicts, males and females must cooperate.
51:20They need each other to bring their genes together in a vital combination, a renewal of life.
51:28All around us live the descendants of a four-billion-year battle for survival.
51:49At the heart of that battle lies sex.
51:58Despite its cost and complexity, its effort and investment, its deception and guile, sex is here to stay.
52:11New life is born every minute, equipped with the right genes from both parents, to survive in an ever-changing world.
52:24The triumph of the mating game is a future for life.
52:33To learn more about what you've seen on this nature program, visit PBS.
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