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SEX Science - Secrets of Attraction - Full HD Movie Uncut
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00:00The moment of conception.
00:06A sperm fertilizes an egg.
00:09It's the start of a new life.
00:12But how did these lovers choose each other?
00:15And why do they turn each other on?
00:20Science is now uncovering the secrets of sexual attraction,
00:24revealing how love is like a rush of cocaine.
00:29How we can choose our future partner with our noses.
00:34And ultimately, how and why we pick our perfect mate.
00:40Boy meets girl.
00:59Girl meets boy.
01:01Each thinks the other is hot.
01:04And the rest just follows naturally.
01:07It's a mating ritual as old as humankind itself.
01:12But now science is moving into the bedroom to study in-depth the details of sexual attraction.
01:19Scientists are putting the chemistry of lust, love and long-term relationships under the microscope.
01:25It's attractive.
01:26It's quite different.
01:27And around the world, researchers are exploring your love life in some surprising ways.
01:34Powerful evolutionary processes determine what attracts us to a mate and the way we attract others.
01:43Natural selection is the struggle for the best individuals to survive.
01:47Animals compete with each other for food and to escape predators.
01:52The survivors win the prize of passing on their genes to future generations.
01:57But there's also another process at work.
02:00Sexual selection.
02:06In all advanced animals, as the saying goes, it takes two to tango.
02:11Only animals capable of attracting a mate will pass their genes down the generations.
02:16So sexual selection encourages the development of features and animal behavior that differentiate male from female and help attract the sexual partner.
02:31Scientists now know that humans are no exception to these rules.
02:37Anthropologist Helen Fisher studies how our bodies and brains have evolved so that boy meets girl.
02:44She believes that three separate sexual drives control the rules of the mating game.
02:51Lust.
02:52The sex drive.
02:54Our craving for sexual gratification.
02:56Romantic love.
02:57Our adoration for the one partner who seems to be all that we seek.
03:08And attachment.
03:09The way we develop a secure union with a long-term partner.
03:17The sex drive evolved to get you out there looking for a range of partners.
03:21I think that romantic love evolved to enable you to focus that maiden energy on just one at a time.
03:26And I think that attachment evolved to enable you to tolerate this individual at least long enough to raise a child through infancy.
03:38But what is it that makes us lust for the opposite sex in the first place?
03:44Yeah.
03:45Fisher has been doing revolutionary research into our brains to discover what turns us on.
03:50For me.
03:51Was you telling me.
03:52On the campus of Stony Brook University, New York, Fisher advertises for students in love.
04:01She uses a functional magnetic resonance imaging, or fMRI machine, to scan the students' brains.
04:09It reveals the constantly changing pattern of blood flow in the brain.
04:14Active brain cells show up as they require more blood than their less active neighbors.
04:20Fifteen years ago we couldn't have studied love this way.
04:23Now we can.
04:24We can look into the brain and see which parts become active and really begin to understand the brain networks that we all experience when we're madly in love.
04:34First, the team records blood flow through the brain as their subjects gaze at a neutral image.
04:41Then they change the picture to a photo of the subjects lover and measure the blood flow once again.
04:47They find that men react differently to women.
04:52Men are turned on visually, while women are more interested in character.
04:57Among our male subjects, we found more activity in a brain region associated with the integration of visual stimuli.
05:06And in our female subjects, we found more activity in brain regions associated with memory recall.
05:11Of course, we've known for generations that men seek visual stimulation when it comes to sex.
05:19Striptease is one of the oldest professions.
05:23For men, visual arousal stimuli are vitally important and activate the brain more than they do for women.
05:30Women do like to look, but men like to look more.
05:35And I think this is for a very profoundly powerful Darwinian reason.
05:41But what are those Darwinian evolutionary reasons?
05:44What exactly are men looking for?
05:49To shed some light on the visual stimuli that fire up a man's brain cells,
05:53we send a researcher out onto the streets of London to demonstrate a classic psychology experiment.
06:01The researcher's mission, to ask men which of these four drawings they find most attractive.
06:07Which of these women do you think is most attractive?
06:10The female figures are virtually identical,
06:13although the small differences between them are all important.
06:17They're the whole size.
06:18No, they're not. There's a slight difference in all of them.
06:20The relationship between the size of the waist and the size of the hips
06:24is marginally different in every picture.
06:27The sex researchers refer to this relationship as the waist-to-hip ratio.
06:32Uh, D.
06:34C.
06:35Uh, C.
06:37I say A.
06:39C.
06:40Any reason why?
06:41She's got curves.
06:42Thank you very much.
06:44In our survey, A wins two votes, B has none,
06:47C attracts 15,
06:50and D scores 5.
06:52Our result is the same as in the original experiment.
06:55A clear majority of men prefer a woman just like Miss C.
06:59A woman whose waist is precisely 7 tenths the size of her hips.
07:04The figure that scientists suggest is the perfect waist-to-hip ratio.
07:07With such a ratio, a woman with a 26 inch waist will have 37 inch hips.
07:15This result may not seem like much, but it gives us an insight as to what men are looking for in a sexual partner.
07:23Women with this waist-to-hip ratio of around 0.7 are thought more likely to bear babies.
07:30They find it easier to get pregnant, conceive earlier in life, and have fewer miscarriages.
07:36These features, along with well-formed lips, high-defined cheeks, and sizable breasts, are controlled by the sex hormones,
07:48and are called hormonal markers.
07:51Biologist Randy Thornhill from the University of New Mexico studies how our bodies display sexual attractiveness.
07:58The human face and body is a collection of signals of symmetry and signals of hormone effects in the body.
08:09Male body testosterone, female body estrogen.
08:13Features such as a woman's breasts and fat deposits in her upper cheeks and lips
08:19are substantially shaped by bodily levels of the sex hormone estrogen.
08:23Secreted primarily by the ovaries, estrogen influences not only the menstrual cycle,
08:31but also the development at puberty of a woman's secondary sexual characteristics,
08:36which include her face and body shape.
08:41Estrogen is a marker of the quality of the female,
08:45and that includes a marker of her reproductive capacity,
08:49so her ability to bear children successfully is all highly estrogen-related in women.
08:58Scientists theorize that men are disproportionately attracted to women
09:03whose features indicate healthy hormonal levels,
09:06because that offers the promise of more easily producing healthy children.
09:09For millions of years, a man needed to mate with a woman who had signs of health and youth and fertility,
09:20the kind of woman that could bear him healthy babies.
09:23But it's not just women who display hormonal markers.
09:26As a boy reaches puberty, testosterone secreted by the testes promotes the growth of particular masculine features,
09:37such as prominent cheekbones, a strong jaw, and broad shoulders.
09:43These masculine features are markers for virility and health.
09:48They also appear to be dominant markers.
09:52Dominance is associated with male reproductive success in many species, including humans.
09:58But sexual attractiveness is transitory.
10:02Estrogen levels decline with age,
10:05which means that a youthful appearance attracts men who are biologically driven to seek out the most fertile women.
10:10But nowadays, all is not what it seems.
10:15It is possible to fool the system by creating hormonal indicator features that nature may not have supplied,
10:22or that age may have taken away.
10:24In 2004, the United States public spent almost $13 billion on cosmetic procedures.
10:31Ninety percent of them were carried out on women.
10:33Dr. Mark Monte is a cosmetic surgeon in what is probably the world's most silicone-enhanced neighborhood, Beverly Hills.
10:44The majority of patients that come to me are fundamentally looking to be more successful in the sexual selection process.
10:52Commonly in women, they're going to be looking for procedures that make them look younger.
10:56And that, again, is because youth is something that is attractive in the process of sexual selection.
11:03Dr. Mark Monte is a younger-looking female is going to naturally be more attractive to any male.
11:08In 2004, plastic surgeons carried out nearly 340,000 breast implants
11:14and around 250,000 face and forehead lifts in the U.S. alone.
11:19But it's not just women who want to cheat nature in the mating game.
11:23In that same year, 1.2 million men had plastic surgery, including 719 pectoral implants.
11:31Things that men look for in plastic surgery are going to be things that make them maybe look more masculine a lot of the time.
11:39For example, a chin implant to make the man have a stronger jaw.
11:43This explosion of personal re-engineering could have a serious effect on human attractiveness in the future.
11:49It actually may make the population more unattractive because people with unattractive features can have them changed and consequently be more successful reproductively.
12:02So their offspring will still have the genes that carried unattractive features on.
12:06But hey, looks aren't everything.
12:09And women more than men seek out other assets.
12:13For women, the ideal mate is more than just a source of fertile sperm.
12:19She seeks the more intangible characteristics, such as reliability, loyalty, kindness,
12:25that suggest a good husband and a good father for her children.
12:30But it's not possible to judge these just from looks.
12:34For millions of years, a woman couldn't really look at a man and size him up to know whether he would be a good provider and a good protector.
12:44Fisher finds a major clue as to how women weigh up their prospective mates by analyzing the brain scans of her female students.
12:54The women in love have more blood racing through a part of the brain called the hippocampus,
13:00an area associated with the processing of memory.
13:03But what has memory got to do with sexual attraction and a woman's love life?
13:13Fisher suggests that women are particularly interested in the men's character
13:19and that they build up a memory map of their behavior in order to determine if they will be a suitable mate and father to their children.
13:27She needed to remember what he did last Valentine's Day, what he promised last Christmas, what he didn't do last summer.
13:34She needed to remember to see if he was going to be a good husband and a good father.
13:40And for that, memory is vitally important.
13:44And in fact, that's what women do all the time.
13:47We get on the telephone and talk to other women, constantly recounting what he did and didn't do.
13:52What we're doing is creating a memory trail of whether this is going to be a good individual to pass on our DNA with.
14:01It makes good evolutionary sense for a woman to mate with a reliable man who will help her raise their children.
14:09But women look for other things in men that will help their offspring succeed, such as status.
14:14Status is important in the mating game, as wealthy, powerful, dominant men are seen as being able to provide a good life for possible offspring.
14:26And they advertise this status with fancy cars and elegant clothes.
14:32But status is only part of the story.
14:40For humankind to survive and prosper, we need healthy offspring, with healthy genes and a healthy immune system to protect them from disease.
14:49But how can you tell if the man or woman you think is attractive will bring a suitable and healthy immune system along to the party?
14:59Scientists suggest that getting your partner to play a little hot and sweaty sport might help.
15:04So you can properly analyze their DNA with your nose.
15:08Evolution has driven men and women to behave in different ways to maximize their chances of winning a mate.
15:18But behavior is only part of the story.
15:21Scientists are now conducting new experiments to decipher more and more of the coded signals our bodies send out to attract a sexual partner.
15:30Signals that contain hidden information about the type and quality of the immune system we may pass on to our children.
15:38And that we read in an instant.
15:43University of New Mexico biologist Randy Thornhill believes that we interpret these signals in milliseconds without even knowing we are doing it.
15:52Our awareness is just, you know, this person is more attractive than that person, when in fact we are doing very sophisticated calculations that are going on in our heads.
16:04And all this is done very unconsciously and very quickly.
16:08He believes the human nose is one of the best tools we have for deciphering secret messages of sexual attraction from the opposite sex.
16:16To illustrate this, Thornhill gets some students to wear identical freshly laundered white shirts during a game of basketball.
16:31As the players perspire, their shirts absorb the sweat, which contains pheromones, odorless airborne molecules exuded from the sweat glands of both men and women.
16:42Pheromones are believed to be involved in attracting the opposite sex.
16:52What Thornhill has discovered is that they have a far more complex role and convey far more complex information than previously believed.
17:03In his laboratory, Thornhill asks a group of female biology graduates to put their sense of smell to the test.
17:09The women will smell these shirts worn by each man and rate them for sexiness, pleasantness and intensity.
17:21The women have no idea which shirt belongs to which athlete.
17:26They take each shirt in turn, sniff and consider its scent and write down which they like best.
17:33Based on nothing more than smell, the girls decide which shirts they find most pleasant and most sexy.
17:43Thornhill analyzes the immune systems of the male and female volunteers by studying the Major Histocompatibility Complex, or MHC, a group of genes that play an important role in the body's defense system.
17:56He discovers that the women's students prefer the smell of men with a dissimilar MHC, thus favoring guys whose immune systems differ from their own.
18:06The general pattern is that both men and women like the body's scent of individuals who are dissimilar, who are different from them.
18:19This makes good evolutionary sense.
18:22The immune system helps fight off disease.
18:25How good it is depends on the genes.
18:28People who inherit a range of genes have an advantage.
18:31Because diseases evolve very, very quickly, you need genetic variation in the offspring to get the right genetic combination to cope with the currently prevalent diseases.
18:46For the perfect match, lovers should have immune system capabilities that differ from each other.
18:53Then their babies get the best of the mix, a diversity giving them a better chance of a healthy life.
18:59Human beings, just like the girls in Thornhill's study, are able to pick a suitable genetic mate just with their noses.
19:15Thornhill's experiments back up earlier European studies that pheromones subconsciously reveal the body's defense secrets to others, although nobody yet understands how this works.
19:25But our noses can detect more than just different genes.
19:30They can also detect symmetry.
19:33It may seem bizarre, but women prefer the smell of men who are more symmetrical.
19:39More symmetric men smell better to women, specifically to women who are at the fertile phase of the menstrual cycle.
19:50The fact that symmetry attracts the opposite sex is nothing new.
19:54It was first noted by researchers in the 1990s, and has proved a popular topic for the media ever since.
20:02The original symmetry studies measured a series of faces to determine how symmetrical they were, then asked people to rate the faces in order of attractiveness.
20:12Thornhill demonstrates this test with a biology class of 2005.
20:19Rate the attractiveness of some male faces, with ten being most attractive and one being least attractive.
20:26Well, I would rate this first individual as about a three or a four.
20:31I think the second picture is a lot more attractive than the first. I'd rate him more as a four or five.
20:36I'd say the girl on the left's about a three, and the girl on the right's a little more attractive. I'd give her about a six to six and a half.
20:42I'd guess the one on the left, I'd put out about a four, and the one on the right, a six.
20:49Like the earlier studies, the faces people thought most attractive were consistently those that were most symmetrical.
20:59What's strange is that if a face is completely symmetrical, like these artificially created by mirroring each side of the face, the result is unnatural.
21:11Perfect symmetry is unattractive.
21:15Scientists do have a theory about why we find symmetrical faces appealing.
21:21Symmetry is a reliable signal of quality because symmetry is very, very difficult to get right.
21:30And hence, symmetry is a marker of the quality of the individual to develop perfect bilateral symmetry.
21:36Recent research from 2004 discovered that our faces reveal hidden clues about our quality as a prospective partner.
21:47Just like the pheromones, faces also display information about our immune system.
21:53In the study, women selected pictures of men they found most attractive.
21:58When they analyzed the blood from the men, they found that the men chosen as the most attractive had a greater variety of genes and hence a stronger immune system.
22:10No one quite knows how our faces convey this information.
22:14It's possible that people with a good immune system are less prone to diseases and parasites.
22:19The sort of things that might lead to asymmetrical features when we are developing.
22:22Whatever the answer, our symmetrical looks, it seems, are the store window in which we advertise the strength of our genes.
22:30The evolutionary process over the last several million years has put into our brains psychological mechanisms that function to assess health of others.
22:44And we interpret that as attractiveness of others.
22:49And that attractiveness corresponds with these health markers, the symmetry, clear skin.
22:57Symmetry appears so important that the female body even performs its own tricks to appear more symmetrical.
23:04In a simple experiment at the University of Liverpool, England, biologists measure the hands and ears of women before, during and after ovulation.
23:14They discover that 24 hours before ovulation, the women's hands and ears alter shape to become more symmetrical.
23:22Scientists are not sure how this happens, but they think it's due to changes in water retention in the cells of the hands and ears.
23:31Because these changes are not the same on both sides of the body, they have the effect of altering the woman's symmetry.
23:39This could be perceived by males as a sudden increase in attractiveness.
23:45But once we have found our future mate, there remains a further mystery that perplexes countless men and women every day.
23:52How do we persuade them to take an interest in us?
23:56Don't despair. It turns out that science can lend a hand by improving your chances of winning in the great mating game with practical, scientific tips to make you more attractive to the opposite sex.
24:11Our range of possible sexual partners and long-term mates is phenomenal.
24:22Every day we pass hundreds of people, any one of whom could turn out to be the perfect partner.
24:27Anthropologist Helen Fisher studies the science of how we choose our lovers, seeking to understand what amazing process of biology makes us fall in love with someone else and then keeps us together long enough to have children.
24:45She has broken down this process of sexual attraction into three stages, lust, romantic love and attachment.
24:59Each of these three sexual drives comes with its own biochemical trigger, one or more hormonal messengers carrying information from one cell to another.
25:10In fact, science now recognizes that a powerful arsenal of chemicals manipulates our decisions without us ever realizing what's happening.
25:25Lust is driven by the hormone testosterone.
25:28Men produce it in their testes, women in their ovaries.
25:33It travels through the blood to the brain and stimulates the sex drive.
25:37It's what drives someone on their first tentative steps toward having sex, seeking their very first date.
25:48But lust can be influenced by other emotions.
25:52Social psychologist Art Aron studies how sexual attraction can be heightened by feelings of fear and anxiety.
26:00When it comes to initial intense attraction, you experience intense physiological arousal.
26:09Your heart beats fast, as would happen if you were running or if something tense or exciting had happened.
26:14These feelings are similar to those caused by fear.
26:24His research suggests that fear and anxiety can initiate feelings of sexual attraction and even make people appear more attractive.
26:32Aaron puts his theory to the test by conducting some, literally, high-level research.
26:41A high and wobbly suspension bridge provides the perfect location for the experiment.
26:46A female researcher stands in the middle of the bridge, a spot chosen as likely to induce a rush of excitement or fear.
26:56She stops passing men and asks them to complete a questionnaire.
27:01The questions are not particularly special, but at the end of the interview she hands each man her phone number in case they have any further questions about the study.
27:10Thanks so much.
27:13In the second stage of the experiment, the researcher changes locations, this time to a low, solid and perfectly safe bridge.
27:24Again, she asks passing men to answer the questionnaire.
27:29Again, at the end of the interview, she gives them her phone number.
27:32The next day, back in the office, she waits by the phone.
27:42She keeps a log of which men call her and on which bridge they had met.
27:49The demonstration appears to support the excitement hypothesis.
27:54Four times more men from the scarier wobbly suspension bridge call than from the safe and solid bridge.
28:03Fear makes the woman more sexually attractive to the men.
28:07So, forget a romantic meal.
28:10Perhaps the best place for the first date is some place really scary.
28:14Man, I can't believe I missed the bus.
28:30This couple is enjoying the first flush of sexual attraction.
28:34Looks like we both did.
28:35It's delightful, but also a little nerve-wracking.
28:39Falling for someone is only half the story.
28:42To take the next step, they also have to fall for you.
28:47Now, scientific theory is all very well, but sometimes you want it to tell you something you can use in the real world.
28:55Something to provoke a little lust, and maybe a little more.
28:59Well, the scientist's first tip isn't exactly revolutionary, but a good tip all the same.
29:06Ever wondered why a candlelit dinner is so romantic?
29:09It might help you look more attractive when you understand the science behind the candlelight.
29:14The answer is in the eyes.
29:17Eye contact seems to be very important.
29:21The more a couple feels in love, the more they will gaze in each other's eyes.
29:25And indeed, much of romantic mythology is associated with gazing in each other's eyes and with the beauty of the eye contact.
29:34What's important is the size of the pupils.
29:39The bigger, the better.
29:40The excitement of meeting an interesting prospective partner releases adrenaline.
29:47That dilates your pupils, causing them to double in diameter.
29:53So when we see dilated pupils, we recognize the signs and subconsciously realize that this big-eyed guy or girl must like us.
30:02Whatever date you go on, science offers other tips to make yourself attractive to your partner.
30:09That doesn't taste like coffee.
30:11Look intelligent.
30:13And be kind.
30:20Evolutionary psychologist Jeffrey Miller researches how sexual selection influences humankind's levels of intelligence.
30:27The funny thing about sexual selection is it's a very powerful evolutionary process, but it's not blind, dumb, natural selection.
30:35It's driven by our tastes, our pleasure, what we find attractive psychologically and physically about other people.
30:44Hundreds of thousands of years ago, humans started selecting partners who were more intelligent.
30:50As a result, intelligence began to grow in our species.
30:53We don't just grow brain for survival, we grow brain to attract other brains as mates.
31:00The evidence that our brain evolved by sexual selection comes from something biologists call the handicap principle.
31:09The peacock's tail is the classic example.
31:12Such a large, colorful tail takes energy to grow.
31:16Resources that could otherwise be put to survival.
31:19It's a handicap, and so only birds with the best genes can carry the biggest, most glamorous tails.
31:27Like a peacock's tail, a bigger brain carries a handicap because it uses a disproportionate amount of the body's energy.
31:36It consumes about 20% of the oxygen we breathe, about 25% of our calories, and about 40% of our glucose.
31:44It's a kind of costly, conspicuous, wasteful organ.
31:50And in that sense, I think of it as kind of being like a luxury good.
31:54And often we're using it for things that aren't that directly related to survival.
31:59We're talking, we're trying to achieve status, we're trying to impress people.
32:03Miller argues that human intelligence and our creativity are the result of our long history of sexual selection.
32:13Our creative imagination, that has produced the rich variety of language, music, art and science we see today,
32:20was forged hundreds of thousands of years ago by our ancestors choosing more intelligent, witty and entertaining partners.
32:30And when we choose a partner, the choice we make will shape the creativity of future generations.
32:36Intelligence helps to show that you've got good genes, because there again, any kind of mutations that tend to reduce brain efficiency tend to reduce intelligence.
32:49But it's not just intelligence that seems to attract us.
32:53It's creative thought.
32:54A recent report from the Royal Society of Biological Sciences found that many artists and poets have twice as many sexual partners as non-creative people.
33:06The study backs up Miller's theory that artists like Picasso are more sexually attractive because of their creativity.
33:14But there is yet another trait that comes out on top as Miller's number one tip for winning them over.
33:20The top two traits most desired across cultures are intelligence and kindness.
33:26In fact, kindness even comes out a little bit higher than intelligence.
33:32Being kind has obvious attractions.
33:35A kind person will make a good partner and will probably be a caring parent.
33:40But there's a more scientific reason for choosing someone with moral virtue.
33:45It's an indicator of good genes.
33:47Moral virtue is costly. It's difficult.
33:52Almost anything that messes up your body or your brain, mutations, brain damage, brain injury, tends to make people more selfish and less kind.
34:02What's more, unlike physical appearance, this type of attractiveness is harder to fake.
34:07It's fairly easy to get your body looking pretty good.
34:12A 40-year-old now can look as youthful and healthy as a 22-year-old a century ago.
34:17To some extent, it's harder to fake the intelligence and moral virtues like kindness that are sexually attractive.
34:25That's what's fascinating about the way we evaluate potential mates is we just automatically focus on the unfakeable indicators of intelligence and kindness.
34:36Over the course of a few dates, this couple engineered ways to show off their genetic gifts to each other.
34:42Some displays are more subtle than others.
34:47Yet neither of them has a clue about what's really going on in their heads.
34:52They say when you fall in love, your eyes light up.
34:57But so do parts of your brain.
34:58And some scientists are now busy exploring the neurochemical fireworks display that explodes in our heads when animal's sexual attraction transforms into love.
35:15What are the secrets of sexual attraction?
35:19The reasons why we think someone's hot.
35:21Science has established that evolutionary cues kickstart the body into lustful behavior.
35:26We are turned on by body shape, symmetry and intelligence.
35:31We are drawn to someone and hope they respond to our advances.
35:35But we don't just mate with anyone.
35:38Usually our brain makes us focus our attention on just one individual.
35:42What fuels this passion for one person is the second of anthropologist Helen Fisher's three mating drives, romantic love.
35:51That feeling of ecstasy so potent, it should carry a warning from the Surgeon General.
35:57Love has always been the preserve of poets and songwriters and novelists.
36:02But I came some time ago to realize that this is one of the most powerful human feelings on Earth.
36:07Romantic love is not a fanciful notion.
36:12It's scientifically measurable.
36:14The result of nature's biological alchemy.
36:19Social psychologist Art Aron and anthropologist Helen Fisher join forces in a unique scientific study.
36:25Their mission? To explore the chemistry of love.
36:30To map the hormones of desire within the architecture of the brain.
36:35Fisher believes that romantic love is the second stage of sexual attraction.
36:41Moving the relationship to something deeper.
36:43If you've ever been in love, you know what an overpowering emotion it can be.
36:52You feel elation, euphoria, mood swings, you're very dependent on the person, you focus your attention on them, you're highly motivated to win them, you crave the person, you become obsessed with thinking about them.
37:06Fisher and Aron are eager to discover if these feelings of romantic love are different from the feelings of sexual arousal.
37:14To find out, they analyze their fMRI data showing blood flow through the brains of students who are self-confessedly deeply in love.
37:22They discover that a region of the brain, known as the caudate nucleus, appears to be activated when a person falls in love.
37:32The caudate is part of the brain's complex reward system.
37:36It appears that being in love affects the brain in much the same way as using certain illegal stimulant drugs.
37:43The response we see in the brain when a person looks at their beloved, who is intensely, passionately in love with them, is very much like the response to having cocaine.
37:56The brain areas concerned have a high concentration of receptors for the hormone dopamine.
38:02Dopamine is a neurotransmitter that is involved in the control of fine motor coordination, motivation, physical energy, short-term memory and emotions such as sexual desire.
38:16Dopamine is one of the body's primary feel-good chemicals.
38:21Elevated levels of dopamine produce extremely focused attention and unwavering motivation.
38:27The very characteristics of romantic love.
38:31It's what we call a reward response, a dopamine system response.
38:38Human beings seem to be wired to have a particular response to very intense reward.
38:44And one of the great examples is falling in love and having it reciprocated.
38:50Heightened dopamine levels explain why love-stricken men and women become so dependent on the relationship
38:57and why they crave to be with their partner.
39:00For Fisher, this desire to focus on just one individual makes perfect evolutionary sense.
39:07This brain system evolved to become triggered so that you could have an incredible amount of energy, focus your attention on somebody, be highly motivated to win them and stay together at least long enough to conceive a child.
39:23The somewhat unromantic truth is that romantic love is born out of the evolutionary success of couples wanting enough sex with each other to get the female pregnant.
39:36Our brains have evolved to feel pleasure in such sexual bonding.
39:41The desire to fall in love seems to be a basic human need across all cultures.
39:47Romantic love is seen everywhere in the world. In one study of cultures around the world, they found evidence of romantic love in over 150 societies.
40:02This is a universal, basic drive. It's a drive that we've evolved to love.
40:08The chemicals flooding our brain during the early stages of love are so powerful that it's little wonder that love is frequently compared to an addiction.
40:19And just like the craving for illicit drugs, love can make people do crazy, sometimes dangerous things.
40:26It's more powerful than the sex drive. I mean, if you ask somebody to go to bed with you and they reject you, you don't kill yourself.
40:35People kill themselves or kill somebody else if they are rejected in love.
40:39Romantic love remains a universal experience, deeply woven into the fabric of the human brain.
40:46Everywhere in the world, people live for love, die for love, sing for love, dance for love, are happy in love.
40:53But Fisher doesn't think that dopamine-fueled romantic love on its own can keep couples together for long.
41:01Romantic love is very metabolically expensive. I mean, you walk all night, you talk till dawn, you make love to the person till noon.
41:09It would be very unadaptive for the human animal to be going constantly in a state of high energy.
41:15Our success as a species depends on men and women sticking together long enough to raise their young.
41:24To try and make sure this happens, our bodies bombard our brains with yet more sexual hormones.
41:31A chemical arsenal that keeps us together long after the fire of romantic love has finally flickered out.
41:40Naked science next asks one of the most provocative questions in evolutionary science.
41:52Can we be faithful to one partner or are we biologically predestined to cheat?
41:58A study of nature's secret weapons of love shows how we are genetically programmed to instantly react to the possibilities of a lustful sexual adventure.
42:13And how our brains feed us a heady brew of powerful drugs to induce the ecstasy of falling in love.
42:19But once we've chosen our mate and fallen in love, can we stay together or are humans biologically programmed to cheat?
42:3097% of all mammals are not monogamous.
42:37So how can we stay together in the face of so many options?
42:41John Gonzaga is a psychologist at UCLA in Southern California.
42:45Gonzaga's studies show that true love really can bind people together in a monogamous relationship.
42:55I think that evolution has given us the capacity to be committed.
42:59But it's complicated because it's not just we either are a species that commits or a species that philanders.
43:06We're a species that has the ability to do both because we react to the environment that we're in.
43:10He has conducted a groundbreaking study to discover how humans stick with their partners rather than go off with any number of attractive alternatives.
43:21So we wanted to directly test whether or not love rather than other states like desire is going to help you push thoughts of attractive alternatives out of your mind.
43:30Gonzaga tests college students who are in a relationship.
43:36He asks them to choose a picture of someone they find very attractive.
43:40Then he asks them to write an essay while thinking of their own partner in a lustful way.
43:46They are instructed that each time they think of the person in the picture, they should put a check in the margin.
43:52He then asks the students to write another essay, this time thinking of their own partner in a loving way.
44:04Again, they put a check in the margin each time they think of the person in the picture.
44:09This time, there are far fewer checks. The students don't feel any lasting attraction to the people in the pictures.
44:20And they quickly forget about them.
44:22In the love condition, people could push the thoughts out of their mind and they wouldn't get this flood of thoughts of attractive alternatives.
44:31What this shows is that true love does seem to bind us together. Real love, that is.
44:41But it's in a constant battle with the emotion of lust or desire.
44:48Desire is a tricky thing because some of the evidence that we have shows that desire, even when it's pointed towards your romantic partner, can make you less committed to them.
44:57So part of its function may be searching the environment for the most attractive alternative that is out there.
45:04If there's somebody who's more attractive out there, that may bode poorly for your current relationship.
45:12So if the relationship is built on love, we are more likely to stick together.
45:18If built on desire, then we are more likely to want to have sex with an attractive other.
45:22It appears that love has evolved to keep us together, while lust is there for us to choose the fittest genes.
45:32So it looks like love, but not desire is the thing that helps you get rid of this problem in committing attractive alternatives and helps you solidify commitment to your romantic partner.
45:43It all fits in with Helen Fisher's belief that the third stage of sexual attraction is long-term attachment.
45:53Attachment is a sense of calm and security that you can feel with a long-term partner.
45:58Love, it would appear, does conquer all. But how does it do it?
46:04The answer is that the body has a natural love potion, ready to stick you and your partner together like glue.
46:11And it comes into play when a couple has sex.
46:15This chemical is called oxytocin, a hormone and neurotransmitter produced in the brain.
46:23It was once believed to confine its effects to inducing labor in pregnant women and stimulating mothers to produce milk.
46:32But now, scientists are discovering other far-reaching effects on both women and men.
46:39Oxytocin acts as a sexual arousal hormone that signals orgasm and prompts cuddling between lovers before, during and after intercourse.
46:53Hence its other name, the cuddling chemical.
46:58This is why when you make love to somebody who you really do like or love, you can feel a sense of cosmic union with them.
47:05That's probably because you've elevated levels of oxytocin, creating this sense of attachment.
47:12It may also serve to strengthen the bond between lovers.
47:16The theory goes that the more sex a couple has with each other, the more oxytocin is released, and the deeper their bond becomes.
47:26This is why it's a little dangerous to go copulate with somebody you don't really like.
47:31In fact, I recommended my various students, don't copulate with somebody who you don't want to fall in love with, because you might just trigger these brain systems.
47:41It is playing with fire.
47:44But nature isn't finished yet.
47:47There is one last important drug in the pharmacy of love.
47:51Vasopressin.
47:52Released during sex, it has a critical role in the long-term commitment stage.
48:02A role discovered when scientists explored the mating habits of the prairie vole.
48:09Prairie voles are among the mere 3% of mammals that mate for life.
48:14Vasopressin is released when the prairie vole mates, just as in humans.
48:19The prairie vole has receptors in its brain for vasopressin in the regions responsible for reward.
48:27Mating stimulates its brain's reward center, and forms a pleasurable memory of that particular mate, and so forms a bond.
48:38Scientists argue the reward mechanism involved in this addiction may well have evolved in a similar way in other monogamous animals.
48:50Humans included.
48:51It could be that like desire and romantic love, forming a lasting loving relationship is simply a matter of chemistry.
49:04Sexual attraction exhilarates and motivates us.
49:07The chemicals that flood our brain, our very physiology, all serve one purpose, the continuation of our species.
49:20Once we have children, these chemicals alter to encourage us to stay together and raise them.
49:27Love is just a part of it.
49:29Sexiness, desire, call it what you will.
49:35It's distilled from an intoxicating hormonal mix, designed to encourage human reproduction.
49:41A chemical cocktail that really does make the world go round.
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