"NARRATOR:" "Every year peacocks shed their magnificent tail feathers." "It must be a relief;" "they're heavy and they attract hungry predators." "(peacock crying)" "But when they grow back, it's perhaps an even greater relief." "Peahens only mate with well-endowed males." "No fancy display, no sex, no passing of genes to the next generation." "That's something every living thing is programmed to do." "It's worth fighting for, maybe even dying for." "In fact, from an evolutionary perspective sex is more important than life itself." "Female praying mantises have been known to turn their dates into dinner." "But every praying mantis alive today had a father who took that risk." "Pacific salmon give everything they have to get upriver to spawn." "Once they've succeeded, they wait for death." "And while we won't trade our lives for sex most of us will risk death to protect our children, the carriers of our genes." "Evolution is a story written over countless generations." "To inherit and pass on genes is to be part of that story." "MAN:" "That's our immortality." "That's what connects us to humans on into the future." "That's what's connected us to all of our ancestors in the past." "That's what connects us to the ancestors that were fish, the ancestors that were protozoans and the ancestors that were bacteria." "It's the single thread that connects all of life on this planet." "NARRATOR:" "Sex and genes... driving behavior, driving evolution." "It's over there." "MAN:" "Here in Southwest Texas roundups have been a big part of history." "I mean, we have cattle roundups..." "Lately we have rattlesnake roundups." "But my crew's not here to look for cattle or rattlesnakes." "We're here to look for a particular species of lizard that, uh, has a different reproductive strategy than most organisms that live on this earth." "MAN:" "Hey, look, there's one!" "WOMAN:" "Right there!" "Right there!" "There it goes!" "There it goes!" "It's going back towards you!" "Ow!" "Shoot!" "NARRATOR:" "Jerry Johnson and his students are after a species made up only of females which give birth without having had sex." "Each egg contains a complete set of its mother's genes." "It develops and grows without any contribution from a male." "And so each baby lizard is an exact copy (a clone) of its mother." "Some people think that they actually have to have some kind of a lesbian behavior where a female mounts a female to get the eggs to develop." "That hasn't been really proven yet but it's... it's an interesting hypothesis." "NARRATOR:" "Regardless of how they do it these lizards have mastered the art of cloning which raises a fundamental question." "As far as these lizards go, the big question, I think is they do so well as all-female species, uh, why is there sex?" "I mean, are males really necessary?" "NARRATOR:" "Immersed as we all are in a culture that extols male courage... grace... self-confidence... passion... questioning the necessity of males is rare." "Men almost never do it and women do it most often in a fit of pique." "Most of the time, we're happy to say, "Vive la différence"" "and get on with things." "But for evolutionary biologists, the question is real." "Given the efficiency of cloning, why would any female put up with the complications of sexual reproduction?" "For starters, males can't bear offspring and rarely share the burden of raising them." "Then there's the fact she only gets to pass on 50% of her genes." "Not to mention all the time, energy and bother involved in courting and mating." "Nevertheless, virtually every new life on the planet is a result of sexual reproduction and not asexual cloning." "Oh, no, it's good for you." "Make you big and strong." "NARRATOR:" "So males must play a critical role and sex must offer an advantage." "Whatever it is, it's buried deep within us." "WOMAN:" "All my life, I've wanted to be a mom." "It's an instinct, it's a feeling, it's something that you just know you want to do." "MAN:" "I've done such a 180." "It's... it's amazing." "I never thought I'd hear myself say that but I really, really wanted to have children." ""Itsy-bitsy spider went up the waterspout."" "NARRATOR:" "Through seven years, multiple operations and more tests and procedures than either cares to remember" "Sharon and J.T. pursued their dream of parenthood." "J.T.:" "She really had this burning desire to have children." "We just didn't want to give up without exploring every possible angle and every possible way of doing it." "And there's... there's a lot of different ways." "I was unaware of how many, you know what science can do nowadays." "I mean, I learned a lot along the way as well." "SHARON TREMITIEDI:" "Nyah is the best thing that's ever happened to me." "I can't imagine my life before Nyah." "WOMAN:" "The biological imperative, as we all know, is to pass on genes." "Most species on Earth use sexual reproduction." "Why do this?" "There has to be some fundamental, biological, evolutionary reason for sexual reproduction." "This has been one of the major questions in biology for a very long time." "NARRATOR:" "For 25 years, Robert Vrijenhoek has been returning to the remote hills of Sonora, Mexico hoping to find clues to the enduring mystery:" "Why sex?" "In this dry and forbidding landscape he seeks those clues in the lifes of fish." "VRIJENHOEK:" "To study the sexual process which appears to be normal, predominant in most things," "I study the diseases of sex, the pathologies of it." "Little fish, in this case, that live in the Mexican deserts that have abandoned the sexual process." "And the beauty of this is it's a natural experiment because side-by-side in these same little puddles we'll have sexual reproducers, we'll have asexual reproducers, all competing in these tiny, little, simple environments." "I could try to study this in a... in a massive environment like an African savanna, but I can't manage an African savanna." "With my capabilities" "I can manage a few small pools like this and for 30 years, I've been coming back to this part of Mexico to study what goes on in these pools." "Ah, we got some." "Very good." "VRIJENHOEK:" "This is a good sample here." "Look how black these fish are." "Wow." "And look at the pigment on them." "NARRATOR:" "Early on, Vrijenhoek discovered that 40% of the minnows in these pools were heavily infected with a parasite that causes black spot disease." "The rest seemed relatively unaffected." "VRIJENHOEK:" "When we brought them back to the laboratory and started counting the spots we noticed, well, my goodness, this is really neat." "The asexual reproducers were taking much higher loads of parasites than the sexual reproducers on average." "Why should they be more parasitized than the sexual reproducers they were living right beside?" "Because they were all being exposed to the same parasites in the water." "There should be no fundamental reason for the different parasite loads on these different kinds of animals unless they had something fundamentally to do with being asexual as versus being sexual." "NARRATOR:" "But what?" "The only thing to do was to keep walking and sampling and thinking." "Oh, look it." "Look at this." "NARRATOR:" "Finally, it hit him." "He was looking at a real-world demonstration of the value of males, one suggested by an evolutionary theory called the "Red Queen."" "VRIJENHOEK:" "The Red Queen is an elegant idea." "I think it's one of the great ideas since Darwin and it goes back to a wonderful scientist, uh, Leigh Van Valen who basically asked about, "Does evolution stop when things get perfectly well adapted to their environment?"" "He said, "Of course not!"" "Evolution is a race and it's much like the race we saw in Alice and the Red Queen in Alice in Wonderland where they were running just as fast as they can and Alice says, "Isn't this curious?" ""As fast as we run, nothing seems to change." "We're staying in the same place."" "And the Red Queen says, "Yes." ""You have to run just as fast as you can to stay in the same place."" "You're living in a complex world, a world full of parasites, a world full of viruses and bacteria, predators, competitive species all basically evolving, too." "And the moment any species stops evolving in response to these challenges and threats, it's doomed." "NARRATOR:" "The cloned fish have stopped evolving." "They're an easy target especially for a short-lived, fast-evolving parasite." "But the sexual fish are a moving target." "Each is a new combination fashioned from its parents' genes." "So as far as the parasite is concerned every individual in that sexual population is a unique and individual challenge." "And that slows down the transmission of the parasite through the sexual part of the population." "NARRATOR:" "Here was a solution to the mystery of sex." "It's the best defense against rapidly evolving enemies." "Or so it seemed until a bad drought dried up the pools, killing the minnows and throwing everything into question." "Eventually the water returned and so did the minnows having slowly worked their way back up the hill from pool to pool." "When Vrijenhoek checked the top pool he made a disturbing discovery." "Now the parasites were decimating the sexual fish." "The clones were doing quite well, thank you." "VRIJENHOEK:" "This is absolutely contrary to anything we'd seen for many years previous to this." "Now it was completely upside down." "Something... something mysterious was going on." "Now an opportunity, you see, to do some science." "Nature had done an experiment for us." "We had to find out what happened, what changed." "We collected the fish." "We can then examine them, uh, carefully and what we found in this case is that the sexual species in the process of recolonization had lost its genetic variation." "It had become inbred." "NARRATOR:" "Testing revealed the sexual fish to be clonelike." "They now resembled each other genetically." "And since they outnumbered the true clones they were being targeted by the parasites." "As a final test, Vrijenhoek conducted a simple experiment." "VRIJENHOEK:" "I went downstream with my bucket into a lower pool where the fish still had genetic variability and I took some fish from there put them in my bucket, hiked back up the mountain and threw them in the pool" "where... where the fish had lost variation and came back a year later just to see what happened." "And it was just wonderful result." "The parasite load in the sexuals had dropped right down to the levels it used to be in the past." "The asexuals now were taking the brunt of the parasite attacks." "And when we examined those sexual fish, we found that we had in fact successfully transplanted genetic variation into that pool." "And, you see, that's precisely the point." "That's what sex does." "Sex generates variability among offspring and when you take that away from a sexual reproducer by inbreeding them or cloning them you've lost the very benefit of sex." "It's that generation of an immense amount of diversity." "That diversity of your offspring provides challenges to everything around it:" "challenges to the parasites, challenges to the viruses, challenges to your competitors." "That's the beauty of the sexual process is the variation and... and wonderful diversity it creates." "NARRATOR:" "The lesson taught by Vrijenhoek's little fish is that passing only half your genes to your kids is a price worth paying." "Sex generates variation which improves a species' chances of survival in a world dominated by relentless competition." "(players yelling)" "For all their downside, males are worth the trouble." "Think of them as a female's insurance policy against losing her children to rapidly evolving threats, like measles and the flu." "If the reason for sex is a bit less mysterious these days its origins remain much more speculative." "Some believe it all got started billions of years ago with two single-celled creatures sharing a chance encounter in the primordial night." "They meet, and genes are exchanged, that's what sex is all about." "The moment is brief but it leaves them a little bit stronger, a little more likely to survive and reproduce." "Males and females came later when random change produced a creature that was small and fast which turned out to be an evolutionary advantage." "Organisms with reproductive cells like that are called "males."" "Their goal is to find organisms with a different specialty, providing the nutrients life requires." "They're called "females."" "These early pioneers evolved in time into sperm and eggs." "Males produce sperm by the millions." "With so many potential offspring it doesn't pay to be fussy about eggs." "A better strategy is to try to fertilize every egg you can." "Eggs are more complex than sperm and take a larger investment of energy." "Females make only a limited number of them." "Fewer eggs mean fewer chances to pass on genes." "And that means females, unlike males do better if they're choosy." "At a deep biological level males and females want different things regardless of how things appear on the surface." "Small sperm versus large eggs;" "quantity versus quality, these are the evolutionary roots of the "war between the sexes."" "This war is a lot more than fodder for poets, philosophers and soap opera writers." "It can explain a lot about how species evolve and why they look and act the way they do." "(frog croaking)" "Charles Darwin was the first to recognize the evolutionary significance of sex." "He came to it because his theory of natural selection had a major problem." "It beautifully explained why all polar bears have heavy coats:" "over time, any trait that improves an individual's chances of survival should spread through the entire population." "But it offered no help in explaining the wild extravagances found throughout nature like the peacock's tail." "WOMAN:" "Darwin had a real problem with peacocks." "In fact, he once said" ""The sight of a peacock makes me sick"" "because he really didn't understand how it could evolve." "NARRATOR:" "An extreme reaction, perhaps but it is hard to see a peacock's tail as something other than an impediment to his survival." "PETRIE:" "They're heavy." "(chuckling):" "They're difficult to carry around." "They take a lot of energy to grow." "They're conspicuous and basically they're going to slow an animal down if it's running away from a predator." "(squawks)" "(tiger growling)" "(growling)" "NARRATOR:" "And it wasn't just the peacock's tail that Darwin's theory of natural selection couldn't explain." "There were also the elaborately ornamented carapaces of beetles and the baroque extravagance of butterflies." "(bird singing)" "And even the delicate songs of birds." "Theologians of his day argued that God created ornate flowers and feathers to inspire man's wonder and devotion." "Darwin was convinced there had to be an evolutionary explanation just as there had to be an evolutionary explanation for why so many of nature's ornaments are seen only on males." "SMALL:" "If natural selection is operating on all organisms the same why is it in nature that you can see differences between males and females?" "And these differences are actually quite large, things like antlers or large body size in males that are clearly connected to maleness or femaleness as if there were two paths." "And this really doesn't make sense if you accept evolution by natural selection." "It should be operating the same on everybody." "It took him several decades to think of it but eventually he happened upon the idea of sexual selection which is really Darwin's most ingenious idea, I think." "These ornaments are not for our good." "They're to advertise each individual's fitness, its goodness as a mate to the opposite sex of its own species." "In a sexually reproducing species survival is no good if you don't find a mate." "If you don't convince somebody that you're good enough to copulate with, to have offspring with your genes will die with you;" "you won't leave any descendants." "(growls)" "NARRATOR:" "Darwin saw two strategies at work in the courtship idiosyncrasies of different species:" "for males, it's competition;" "for females, it's choice." "Males fight for access to, or control over the females themselves, or a resource females need like food or territory." "(screeching)" "Sometimes this competition gets downright nasty." "But it's just as likely the males of a species will follow the path epitomized by John Travolta in Saturday Night Fever the path of the peacock, seduction through sexual display." "(Bee Gees performing "Night Fever")" ""Reach out for me..."" "NARRATOR:" "This is where female choice comes in." ""No"" ""No-o-o..."" "SMALL:" "Female choice is that part of sexual selection that has to do with females choosing particular males over others." "(emphatically):" ""No!"" "(song ends)" "You would expect that the female who invests more per egg, per offspring, should be much more choosy about who she has offspring with, who she combines her genes with." "Whereas the male, who is investing so little, you would expect that he wouldn't care so much." "NARRATOR:" "Darwin's contemporaries had no trouble with male competition." "But females actively directing evolution through their choice of mates?" "That was too much." "MILLER:" "This was the aspect of sexual selection that Victorians really had trouble with." "They couldn't imagine that mere female animal brains could be shaping something as... as grand and important as evolution itself." "In those days, females didn't have choices." "Males decided who they were to marry, for example, you know and females really didn't actually have that much say in the matter." "(peahens calling)" "NARRATOR:" "So radical was the idea of female choice that it was more than a century before anyone tested it." "Marion Petrie's experiments with peacocks were among the first." "According to sexual selection theory peacocks grow their tails because peahens pay attention to them and peahens pay attention because only a healthy, fit, strong peacock can afford to grow one." "Yeah, he's got a lovely tail." "NARRATOR:" "To test that, Petrie measured the tail lengths of a captive population of peacocks." "PETRIE:" "The longest feather is 145." "NARRATOR:" "Then she charted exactly which males the females chose over an entire mating season." "Her data left little doubt:" "to peahens, size matters." "Next, Petrie tried reducing the number of eyespots in some otherwise well-endowed tails." "The result was a lonely mating season for the trimmed birds." "Finally, Petrie started playing matchmaker." "PETRIE:" "We paired females with males with big trains and we paired females with males with small trains and then we looked at how being paired to a male with a big train... what effect that had on the performance of the female's offspring." "And what we found was is that if you were mated to a male with an elaborate train your offspring survived a lot better." "Paternity does matter." "(peafowl squawking)" "NARRATOR:" "Peacocks are a classic case of evolution operating through sexual selection." "Males compete for the opportunity to mate and females hold out for the best genes." "When females choose a trait that is an honest indicator of good genes that trait spreads throughout the population over generations." "It can also become highly exaggerated." "It's all a logical consequence of the differing reproductive strategies of males, who have lots of sperm and females, who have fewer eggs." "But the goal isn't just to have offspring, the young have to survive long enough to have their own offspring." "Sometimes, that requires paying as much attention to behavioral traits as to physical ones." "Lizzie, it's lonely as dyin' out there." "Will you come with me?" "NARRATOR:" "In the Hollywood classic The Rainmaker" "Katherine Hepburn's struggle to choose between the sexy, quick-witted Burt Lancaster and the dependable Wendell Corey mirrors a deep biological dilemma." "For some species, the chances of offspring surviving increase if a female chooses a mate who'll stick around over the one with the best genes." "Evolution has favored in many of the species Stephen Emlen studies males and females who share the job of parenting." "(birds twittering)" "EMLEN:" "In songbirds if a male were to be a deadbeat dad and leave and not raise the kids the kids would die, and basically no genes would be passed to the next generation because the female alone can't do it." "NARRATOR:" "She needs help." "But he's only going to give up philandering if he believes the chicks he's staying home to help raise are his own." "The result is monogamy, a social solution to a biological dilemma." "Human infants are also born heavily dependent on parental care." "You can't get it quick enough, huh?" "It's not coming out fast enough for you?" "Let's try this." "JOSEPH TREMITIEDI:" "Being a parent is about bringing up the child, loving the child sacrificing for the child and Nyah..." "I would give my life for her without blinking an eye." "Everything we do revolves around her." "Our needs are second." "What she needs comes first." "NARRATOR:" "A shared investment in the next generation can reinforce a couple's commitment to each other." "What she gave us was completeness;" "that it wasn't just him and I anymore, it's the three of us and, you know, we like the way that sounds, you know." "NARRATOR:" "But monogamy isn't easy to maintain." "While some evolutionary forces encourage it others threaten the family values that are at its core." "Songbirds are unusually monogamous." "But even as they pair off and set up nests inevitably, some of them are lusting after their neighbors." "EMLEN:" "Say here in an Ithaca woodlot you migrate back from South America and of the 100 birds in this woodlot of your species you're the 65th female to return from migration." "You find that most of the males have already been taken." "You choose the best male available but you end up paired with a fairly low-quality male in comparison with your neighbors." "You're in a situation where you now have a social mate who's going to help provide the food and the care for your young but the neighbors are in fact higher genetic quality, perhaps more experienced, more healthy," "and if your young could be sired by them you in fact would have healthier young that carry, therefore, the genes to promote and have healthier grandchildren." "NARRATOR:" "But for a female songbird, cheating is a risky strategy;" "if she's caught, her partner will leave." "Alone after the chicks are born she won't be able to meet their needs." "(chicks cheeping)" "Yet a surprising number of songbirds take that risk." "DNA testing has revealed that as many as 40% of all chicks are not sired by the male that helps feed them." "Cheating, at least for certain female songbirds gives their chicks better genes, and therefore a better chance of surviving until they can reproduce." "For the wattled jacanas of Panama survival of chicks is so uncertain it's led to an amazing gender role reversal." "Jacanas lose a lot of chicks to crocodiles." "They might have died out long ago if they hadn't found a way to produce more offspring." "Their solution:" "the female lays the eggs but it's the male who keeps them warm and raises the chicks." "EMLEN:" "If a female is the one who is freed of parental care she can produce more eggs more rapidly and both she and the male benefit from that." "NARRATOR:" "As jacana females cut back on nurturing their reproductive strategy began to change." "Now it's the females who care more about quantity than quality." "Now it's the females who fight over mates." "Over time, they've taken on traditionally male characteristics." "It's the females that are larger females are highly aggressive females compete for access to males and a highly "successful" female is one who is able to accumulate and defend, if you will a harem of four or even five mates." "NARRATOR:" "When a female conquers another's territory she often breaks the eggs and kills the chicks of the vanquished mother." "EMLEN:" "This makes sense, despite its grisliness." "The male instantly becomes available to take her eggs and in fact that's what happens." "Within hours, the female is sexually soliciting to the male." "He starts mounting, and within a few days to a week he has a clutch of eggs that are her eggs." "NARRATOR:" "So here is an evolutionary revelation about gender:" "male and female roles are not set in stone." "They're largely determined by which sex competes for mates, and which invests in the young." "Solving the problem of how to pass on your genes can even trigger the emergence of a new species." "On the tree of life different branches are often occupied by species that look poles apart." "But sometimes, what separates species is more social than physical as it is with our closest relatives chimpanzees and bonobos." "Chimpanzees and bonobos live in similar jungles in equatorial Africa." "They look alike, live in the same size communities and eat similar foods." "Yet... (chimpanzees shrieking)" "Violence is a fact of life for chimpanzees." "Battles between neighboring communities are common." "So is the physical abuse of females by males." "Bonobos, on the other hand, are essentially peaceful." "In all instances bonobos are predisposed to make love, not war." "So why are humankind's closest relatives so different?" "For 20 years" "Richard Wrangham has searched for an answer to that among the chimpanzees of Uganda's Kibale Forest." "WRANGHAM:" "Chimpanzee society is horridly patriarchal, horridly brutal in many ways from the female point of view." "I mean, the young males, the late adolescents... it's almost a rite of passage for them." "In order to be a..." "an adult male chimpanzee you have to be able to dominate all of the females." "So that's rough from the female's point of view." "They regularly get beaten up in horrid ways." "NARRATOR:" "Wrangham frequently finds himself in the middle of what, for want of another term, must be called a domestic dispute." "(chimpanzee shrieking)" "WRANGHAM Imoso's... chasing Barbara." "He wants to have some sex." "Barbara's a young female and she's quite upset about being approached by the dominant male for sex." "She's only used, really, to mating with young boys." "(shrieking continuing)" "There's our alpha male, Imoso." "He's not used to being denied, and now he's after Tongo and with his erection, his penile erection, his hair erection, he really wants to get at Tongo but for the moment she's escaped successfully." "(cacophony subsides)" "NARRATOR:" "Females chimps aren't the only ones at risk." "Infanticide is thought by primatologists to be a major factor in the evolution of chimpanzee sexuality." "As a response to this danger females try to copulate with all the males in the troop." "The grisly logic of infanticide is disrupted if every male thinks every infant might be his." "WRANGHAM:" "Under this regime in which the females are trying to get matings from lots of different males then it's favored males to have these tremendous testes and large seminiferous tubules for storing the sperm so they can put in a tremendous number of sperm," "about five times as many as humans." "It's very high-quality sperm." "If you look at human sperm, you know, the classic quote is from the vet who picks up a slide of human sperm and says" ""If this was a bull, I would shoot it."" "But chimps, by comparison to humans have very high-quality sperm and they can have five or more copulations per day." "The whole thing only takes seven seconds, though." "I mean, this is not fun sex by human standards." "NARRATOR:" "Bonobos, on the other hand seem to find sex thoroughly enjoyable." "For the past decade" "Amy Parish has been observing bonobo behavior at the San Diego Wild Animal Park." "She's seen them go at it in every way imaginable." "PARISH:" "You get standard heterosexual interactions which are often face-to-face, the way they are in humans." "You also see what we call ventral upright matings where a male and a female will hang together out of a tree suspended, and have sex." "Males have sex with other males in what we call "rump-rump rubbing"" "where they stand and rub their scrotums together." "We also see something among males called "penis fencing"" "where males will suspend off of branches by their arms and rub their erect penises back and forth." "And then a very remarkable behavior in which two females rub their genital swellings together in rapid sideways motions." "(bonobos panting)" "NARRATOR:" "So what's allowed bonobo females to establish such peaceful relations with males?" "Parish believes the answer is female solidarity." "(bonobos shrieking)" "PARISH:" "By cooperating with each other and solidifying their bonds and reducing any tension that does exist they're able to form alliances with each other and cooperatively dominate males and this changes the whole balance of power and the whole social dynamic in the group" "and makes it radically different from chimpanzees." "NARRATOR:" "And why have bonobo females evolved this strategy and chimpanzee females haven't?" "It looks as though a relatively simple change in the feeding ecology is responsible for this dramatic difference in sexual behavior." "The bonobos live in an environment where you have herbs much more continuously on the ground." "And there are chimpanzees that live in similar forests but wherever those forests are occupied by chimpanzees they're also occupied by gorillas." "NARRATOR:" "The gorillas eat the food on the ground leaving the chimpanzees heavily dependent on fruit trees." "To get their share, the female chimps forage alone." "WRANGHAM:" "Mothers, with their babies ranging in age from one to about five can't move as quickly as the males." "I mean, one infant is up here playing in the tree and a couple are nibbling slowly and the mothers have to sit and wait for them." "So it's absolutely typical that the males reach the big feeding ground first and the males have finished all the food by the time the mothers arrive." "So the mothers disperse, away from each other and away from the males and that means they can't have much opportunity to form bonds with each other." "NARRATOR:" "The simple fact that there was food available on the ground appears to have been the force that drove the evolution of bonobos." "Wrangham believes the catalyst was a long-lasting drought two million years ago, in what is now Zaire." "The plants, and the gorillas that depended on them, died." "It was tough on the chimpanzees;" "but they could live on the fruit in the trees." "When the rains and the plants returned, the gorillas didn't." "Now the chimpanzees could get to the food on the ground." "In time, they evolved into bonobos." "It's been suggested that same drought forced our ancestors out of East Africa's forests and onto the plains." "WRANGHAM:" "And once you had drying in a savanna area then conditions became quite harsh." "It was impossible for early humans to travel around in groups together in the way that bonobos do and therefore for females to form alliances and dominate the males in the way that happens in bonobos." "But a little bit different climatic history, a little bit different in our food history and we might have evolved to be a totally different more peaceful, less violent, more sexual species." "NARRATOR:" "Today, this theory is little more than interesting speculation." "But the idea behind it is consistent with a growing but controversial body of scientific thought that claims much of present-day human behavior is rooted in our distant past." "There's a new group of scientists called evolutionary psychologists and they're interested in how human evolutionary history affects the way we think today." "Now, keep in mind that that means four million years of evolutionary history, a time during which we were almost always roaming the plains and forests of Africa." "How does that affect the way we operate today?" "They've been looking at things like mate choice different kinds of standards of beauty, social exchange." "And they have a very long way to go before they can prove some of their ideas." "But they're still some of the most interesting and provocative issues around today." "NARRATOR:" "Evolutionary psychologists begin by pointing out that regardless of the culture in which we grow up we all tend to respond the same way to a surprising variety of things." "Most of us find spiders unpleasant, certain body types sexy and particular smells disgusting." "All, they say, are legacies of our evolutionary past." "MAN:" "If we ask, for example do rotten eggs smell bad?" "It's just a molecule." "Hydrogen sulfide gas, it doesn't have a smell." "We have evolved a brain to generate a negative feeling for something that's detrimental to our gene survival." "This indicates biological contamination, right?" "If you were a dung beetle the smell of rotten eggs might smell wonderful to you because the smell doesn't reside in the molecule;" "it resides in the evolved brain." "NARRATOR:" "To an evolutionary psychologist it's no accident Hollywood turns to snakes when it wants to put a hero in danger." "Snakes." "Why did it have to be snakes?" "(thunder cracks)" "NARRATOR:" "Dangerous snakes don't slither into most of our lives." "Still, more than a few of us share" "Indiana Jones's instinctual fear." "You go first." "NARRATOR:" "Another deeply embedded instinct we may have inherited from our ancestors is the ability to smell a genetically compatible mate." "In one unusual experiment scientists had young men sleep in the same T-shirt for a couple of nights until the shirts were infused with their unique smell." "It turns out, when women were asked to rate the sex appeal of the different men based only on the smell of the shirts they consistently rated higher the shirts of men whose immune genes were unlike their own." "From an evolutionary perspective, this makes sense." "Choosing a mate with different immune genes gives offspring a greater protection against viruses parasites and other pathogens." "The ability to smell good genes is a remarkable talent but like most instincts, we don't even know it's at work." "We just like the way someone smells or the way they look, or because they make us laugh." "People don't have sex because they want to perpetuate their genes." "They don't like someone because they want to get better genes." "They do things because they feel good to them." "They have sex because it feels good." "The relationship between those good feelings and gene survival may not even be known to them." "They never think about that." "They do things because it feels good and they never think, "Why do those things feel good?"" ""Why have we evolved a brain" ""that makes certain things feel bad to us or certain things feel good to us?"" "And that's the question that we're addressing." "NARRATOR:" "Like many men, Victor Johnston spends as much time as he can looking at beautiful women." "But for Johnston it's an academic pursuit, part of his effort to understand the evolutionary roots of beauty." "You have to remember that beauty is a bit like sugar." "In a hunter-gatherer world, the source of sugar was ripe fruit so if you liked the taste of sugar you got a very nutritional diet." "And now we've separated the sugar from the nutrient the sugar's actually killing us, it's bad for us and yet we still have this preference for it." "Well, beauty may be something the same." "Beauty's just a configuration of facial cues that we find to be attractive." "These are cues that are telling us something about that individual, something biologically important." "People like very full lips and these are due to estrogens at puberty." "And they also like females with short lower jaws and narrow lower jaws and this indicates a low testosterone level." "And that combination of high estrogens and low testosterone is correlated with fertility." "In a hunter-gatherer world it was important to detect these cues but in today's world, you know, we can manipulate fertility." "We have fertility drugs and contraception." "It doesn't have the same importance but we still react to it;" "it still affects our behavior." "The next face I want you to find, Sarah, is the face that would be the most attractive male face." "Whoo-hoo!" ""The most attractive male"..." "Yeah, the most attractive male face from this range of faces." "NARRATOR:" "To study facial preferences" "Johnston constructed a computer program that scrolls seamlessly between a sexy, fertile female face and a macho, virile male face." "SARAH:" "That guy looks like he's right out of prison." "He's not very popular." "Yeah, he's not very popular." "I'd like for you to find the best possible mate for a short-term relationship." "Short-term, okay..." "RESEARCHER:" "A secret weekend." "Tends to be more masculine and... pretty far down there." "JOHNSTON:" "For a short-term mate they want someone who's got a lot of testosterone markers on their face compared with a choice for a long-term mate." "So whenever people are looking for good genes or a short-term relationship they seem to be looking for these more masculine characteristics but not so when they're looking for a long-term mate." "They're looking for, maybe, a softer, kinder person for a long-term relationship." "WOMAN:" "Maybe someone that's kind of a little bit protective, help me out, watch over us." "NARRATOR:" "Johnston tested many of his subjects more than once." "To his surprise he sometimes got different answers on different days." "When was the first day of bleeding for your last period?" "NARRATOR:" "It turns out that when women are ovulating and the chances of getting pregnant are high there is a consistent shift in what they find attractive toward a more masculine-looking male." "I want someone at least my age." "NARRATOR:" "Just like with the songbirds, that's when the unconscious lure of those "good genes" is strongest." "WOMAN:" "There, that's the one." "NARRATOR:" "Of all the claims of evolutionary psychology none are more sweeping than Geoffrey Miller's." "He believes the human brain like the peacock's magnificent tail is an extravagance that evolved, at least in part to help us attract a mate and pass on genes." "The human brain is the most complex system in the known universe." "It's wildly in excess of what it seems like we would need to survive on the plains of Africa." "In fact, the human brain seems so excessive that a lot of people who believe in evolution applied to plants and animals have real trouble imagining how natural selection produced the human brain." "All the other species on the planet seem to get by with relatively small, simple nervous systems that seem tightly optimized just to do what the species needs to do to get by." "I think people are perfectly sensible in being skeptical about the ability of selection for survival to account for the human brain." "I think there was a sort of guidance happening, there was a sort of decision-making process that was selecting our brains." "But it wasn't God, it was our ancestors." "They were choosing their sexual partners for their brains for their behavior, during courtship and I think our semi-intelligent ancestors were the guiding force." "They were the guiding hand in human evolution." "NARRATOR:" "When choosing a mate, we still notice beauty but what really counts is how someone thinks, feels and acts." "All of these are products of the brain." "SHARON TREMITIEDI:" "He's a sweet, gentle man, and he makes me laugh." "I don't think I'd tell him that, but... because there's times he doesn't make me laugh, but..." "He has really nice qualities about him." "He was funny, he's kind, he's generous." "He has all the good qualities I think you want in a mate." "Her sense of humor, her laugh." "She always seemed to be upbeat, always happy and she has a great personality." "Plus she's a very attractive woman." "I mean, I'm not going to lie." "That had a lot to do with it as well." "You've never spoke to me like this." "I tell you there comes one moment once and heaven help those who pass that moment by when beauty stands looking into the soul..." "NARRATOR:" "In the classic tale of Cyrano de Bergerac his eloquent words convince the beautiful Roxanne there's more to him than his extraordinary nose." "It's brains, not beauty, that win her heart." "Your name is like a golden bell hung in my heart and when I think of you, I tremble and the bell swings and rings..." "MILLER:" "Everybody who falls in love knows that they're falling in love not just with somebody's physical features but their personality, their intelligence, their creativity, their wit and their charm." "Yes... that is love." "CYRANO:" "Yes, that is love." "There are all sorts of things that mess up brains and paradoxically for that reason brains make really good indicators of how fit you are during courtship." "In fact, they're probably better indicators of that even than a peacock's tail is of how fit a peacock is." "Geoffrey Miller's idea about sexual selection moving us down the path of larger brains is really interesting because it's not the same old saw of tool use, language, culture;" "it's something entirely different." "Now, I have some questions about what's the female role in this, how do women fit into this process?" "But still, it's a very intriguing idea and he might just be right." "(chorus singing Handel's "Hallelujah Chorus")" "NARRATOR:" "Miller is just getting started when he argues that the size of our brains can be attributed to our ancestors' sexual choices." "He's also convinced that artistic expression no matter how sublime has its roots in our desire to impress the opposite sex." "("Hallelujah Chorus" continuing)" "And that includes music, art, the poetic and storytelling uses of language... even a good sense of humor." "(studio audience laughing)" "NARRATOR:" "According to Miller they all stem from our instincts for sexual display." "MILLER:" "I think when a lot of people produce cultural displays what they're doing, in a sense is exercising these sexual instincts for impressing the opposite sex." "They're not doing it consciously but what they're doing is investing their product with an awful lot of information about themselves." "(classical ballet music playing)" "A lot of people are very upset about this idea that cultural displays are there to attract sexual partners." "They find this somehow demeaning as if sex is dirty and culture is clean and the two must be kept separate." "I think this is a basic mistake." "I think the capacity for artistic creativity is there because our ancestors valued it when they were making their sexual choices." "NARRATOR:" "Miller knows his ideas about art, culture and the human brain are controversial." "He's also convinced that, as experimental techniques improve it'll be possible to determine whether he's right or wrong." "(birds squawking)" "Sex is at the heart of evolution." "The process of mixing and passing on genes produces variation that helps species meet the challenge of life in a competitive world." "Sexually selected variations are those that help individuals find mates and successfully raise young." "That's how, for humans sex became fun and parenting rewarding." "Those of our ancestors who took pleasure from sex and satisfaction from parenting had more surviving offspring than those who didn't;" "that was true generation after generation." "These traits are now almost universal." "Even if we choose not to have children, we still enjoy sex." "And even when we adopt a child who doesn't carry our genes we can still find parenting rewarding." "SHARON TREMITIEDI:" "The infertility specialist said to try a different option, and so that's what we did." "She's my baby." "The fact that Sharon didn't bear her or I didn't father her, that's the physical thing." "Parenthood is so much more than the physical." "The physical's the easy part." "Tell Mommy, "I want a satellite dish."" "Yeah... tell her that's what you want because that's the only way I'm going to get it." "SMALL:" "Humans are the only species in which adults will care for children who are not biologically related to them, over the long term." "With our highly intellectualized brain we have taken this compelling biological urge to mate and reproduce and care for children and translated that onto children with whom we share no genes in common." "JOSEPH TREMITIEDI:" "I tease Sharon; she's the new woman in my life." "I never thought I'd fall in love with another woman but she's the new woman in my life and I wouldn't have it any other way." "NARRATOR:" "Humans are unique." "We're a product of evolution but we've taken the first tentative steps towards controlling our evolutionary destiny." "It's a brave new world we're entering." "Only time will tell if we'll be as successful at guiding our future as evolution has been." "BOTH (quietly):" ""Out came the sunshine and dried up all the rain"" ""And the itsy-bitsy spider went up the spout again."" "Continue the journey into where we're from and where we're going at the Evolution web site." "The seven-part Evolution boxed set and the companion book are available from WGBH Boston Video." "To place an order, please call:"