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14. What Motivates Us: Sex — Transcript

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0:12Professor Paul Bloom: Sex is really strange.
0:21You ask people, "What's your favorite
0:25activity?" and if you ask people,
0:28particularly college students, particularly just fresh from
0:33spring break – I've seen teen movies – they'll often answer,
0:40"Sex." or some word that is synonymous
0:44with sex. But there's a kind of a puzzle
0:48about how much time we spend on sex.
0:53And it turns out there is data on this.
0:56So, people say sex is their favorite activity,
0:59but it turns out we actually know how much time the average
1:03American spends on sex. And the data I'm going to
1:07follow from was summarized in this wonderful book by James
1:12Gleick: Americans tell pollsters
1:15their single favorite activity is sex.
1:17In terms of enjoyability, they rank sex ahead of sports,
1:21fishing, bar-hopping, hugging and kissing,
1:24talking with the family, eating, watching television,
1:28going on trips, planning trips,
1:30gardening, bathing, shopping, dressing,
1:32housework, dishwashing, laundry, visiting the dentist,
1:36and getting the car repaired. On the other hand,
1:39these same studies suggested the average time per day devoted
1:45to sex is four minutes and three seconds.
1:49[As Gleick says,] This is not much,
1:52even if the four minutes excludes time spent flirting,
1:58dancing, ogling, cruising the boulevard,
2:01toning up in gyms, toning up in beauty parlors,
2:04rehearsing pick up lines, showering, thinking about sex,
2:07reading about sex, doodling pornographically,
2:11looking at erotic magazines, renting videos,
2:16dreaming of sex, looking at fashion magazines,
2:19cleaning up after sex, coping with the consequences of
2:22sex, building towers or otherwise
2:24repressing, transferring, and sublimating .
2:31And I like this passage because it illustrates two points,
2:35two important points. One is we don't actually spend
2:38that much time on sex. In fact, the four minutes and
2:41three seconds is an interesting number because when you do times
2:46studies on how much Americans spend filling out tax-related
2:50forms for the IRS, it's four minutes and a few
2:54seconds. But the passage also points out
2:57that regardless of the brute time we spend on it,
3:00it is extraordinarily important.
3:03Everything in life follows from it – marriage,
3:06family, children, much of aggression,
3:09much of competition, much of art and music and
3:13creative pursuits. Much of everything follows from
3:17it. If we were a creature without
3:19sex, everything would be different.
3:21And what's interesting is, there are creatures without
3:24sex. There are creatures that
3:27reproduce by cloning. And in fact,
3:29this basic fact about people – that we fall,
3:32roughly, into males and females – is an evolutionary mystery.
3:37It's not clear why animals that are somewhat large have two
3:42sexes. From a biological Darwinian
3:45perspective, having two sexes is bizarre because each time you
3:48have an offspring you toss away half your genes.
3:51My children only have--each of them have half my DNA.
3:55If I were to clone, they would have all of it.
3:58And so, it's a puzzle how sex ever evolved.
4:02This is not a course in evolutionary biology,
4:04and that's not the puzzle we're going to be looking at today.
4:07We're going to look at a few questions.
4:10First, we're going to talk from first a theoretical point of
4:13view and then an empirical point of view about how males and
4:17females are different. Then we're going to talk about
4:20sexual attractiveness, some research about what people
4:23find to be sexually attractive, and then we'll talk a very
4:26little bit at the end about the origins of sexual preference:
4:29why some people are straight, others gay, others bisexual,
4:33and others harder to classify. Now, of all the topics I'm
4:38presenting, sex is one of the sort of dicey ones from an
4:42emotional point of view. These are difficult issues
4:47because sex is, by definition,
4:50an intimate part of our lives, and it matters a lot.
4:56Moreover, sex is fraught with moral implications.
4:59And since I'm talking about this from, at least at the
5:03beginning, from a Darwinian evolutionary perspective,
5:06I'm obliged to start off by dealing with some of the moral
5:10consequences and moral implications.
5:13So, for instance, many biologists – all
5:16biologists I would say – will have argued that sexual
5:21behavior, sexual action,
5:24sexual desire is, to some extent,
5:25a biological adaptation existing to spread our genes.
5:29From that perspective then, non-procreative sex –
5:33including gay sex, sex with birth control,
5:37sex by post-menopausal women – does not serve this
5:43reproductive goal and, in some sense perhaps,
5:47is unnatural. And one might argue then,
5:50"Does this mean it's wrong?" We'll also be talking about sex
5:54differences, differences between men and women,
5:56for instance, in how much you want anonymous
6:00sexual encounters, differences between men and
6:03women in social intelligence, in aggression and empathy.
6:07And regardless of what you think about these differences,
6:11whether you think they're right or wrong or it doesn't matter,
6:16you'll ask the question, "To what extent are they
6:19mutable?" That is, if they exist through
6:22Darwinian natural selection, to what extent can we ever get
6:26rid of them? And I want to address those two
6:30issues, the issues of morality and inevitability,
6:33from the very start. And I want to start off
6:36with--for each of them have a quote by a prominent
6:40evolutionary scholar. So, the first one is by Steve
6:43Pinker in How the Mind Works.
6:45And he writes, Nature does not dictate
6:49what we should accept or how we should live our lives.
6:52Well into my procreating years, I am so far voluntarily
6:55childless, having squandered my biological resources reading and
6:59writing, doing research,
7:00helping friends and students, and jogging in
7:03circles--ignoring the solemn imperative to spread my genes.
7:06By Darwinian standards, I am a horrible mistake,
7:09a pathetic loser, but I am happy to be that way,
7:13and if my genes don't like it they can go jump in the
7:17lake. Pinker's point,
7:18I think, is a reasonable one. It is true that certain things
7:22we do exist to serve the dictates of natural selection,
7:26but that doesn't make them right?
7:28If you think that something is only right if it leads to the
7:33generation of more genes, if it leads to reproduction,
7:36then you're not going to think very much about birth control.
7:39You're not going to think very much about any sort of
7:42non-procreative sex. On the other hand,
7:44if you're--Moreover, if you think something's wrong
7:47if it's unnatural, you're going to think much
7:51about flying in a plane or refrigerating food or surviving
7:54a severe infection. More generally,
7:57our bodies and brains have evolved for reproductive
8:00success, but we can use these brains to choose our own
8:03destinies. Nothing moral necessarily
8:06follows from the facts of biology.
8:08That's all I'm going to say about morality.
8:12But I want you to keep it in mind when we discuss different
8:15claims about what's evolved and what hasn't.
8:17What about inevitability? Here I want to turn to Richard
8:22Dawkins. Richard Dawkins writes,
8:24If a child has had bad teaching in mathematics,
8:27it is accepted that a resulting deficiency can be remedied by
8:30extra-good teaching in the following year.
8:33But any suggestion that the child's deficiency might have a
8:35genetic origin is likely to be greeted with something
8:38approaching despair. If it's in the genes,
8:41it is determined and nothing can be done about it.
8:44This is pernicious nonsense on an almost astrological scale.
8:48Genetic causes and environmental causes are in
8:50principle no different from each other.
8:53Some may be harder to reverse, others may be easy.
8:55What did genes do to deserve their sinister,
8:58juggernaut-like reputation? Why are genes thought to be so
9:02much more fixed and inescapable in their effects than
9:05television, nuns or books. I like the nuns.
9:09And the point here is what causes something is logically
9:16separate from what can reverse it.
9:21And you can think of clear cases where something is plainly
9:25genetic but is fairly easily reversed and where something is
9:29cultural and is very difficult to reverse.
9:32Here's an example. My eyesight is quite poor.
9:36The reason why my eyesight is quite poor is not due to the
9:40patriarchy, television, culture or "the man."
9:44Rather, my eyesight is quite poor due to the crappy genes Mom
9:48and Dad gave me. It is genetically determined if
9:50anything is. It is also fairly easy to fix.
9:53There are these machines where they put panes of glass in front
9:58of your eyes and help you to see better.
10:01More advanced machines known as contact lenses actually stick
10:04the thing into your eyes, and at the cost of occasional
10:07infections you come to see better.
10:10It's biologically caused but fairly easy to fix.
10:15On the other hand, take an example of society's
10:18treatment of the obese. It turns out when we – and
10:21we'll get to this a little bit when we talk about sexual
10:25attractiveness – how thin somebody is or how fat they are;
10:29what you think of that is actually not particularly
10:32hard-wired. It varies a lot from culture to
10:34culture. But once it's in a culture,
10:36it is almost impossible to shake.
10:39So, the point, there is just that genetic does
10:43not mean inevitable, and cultural does not mean easy
10:48to fix. Okay.
10:50That's general background. Let's start with basic Sex Ed.
10:53What's the difference between males and females?
10:56Well, don't even think penis and vagina.
11:02There are a lot of animals that have neither one.
11:05And the difference actually runs deeper.
11:07By definition, when biologists talk about
11:10this, animals that are males have a little sex cell,
11:14which carries genes and nothing else – sperm cells.
11:19Animals that are females have a big sex cell,
11:22which has genes but also food and a protective cover and all
11:26sorts of other stuff. Typically, the little sex cell
11:30is much littler than the big sex cell.
11:32This is the only erotic picture I'm going to show you today.
11:36It's a bunch of these little sperm circling around the egg.
11:42It's romantic. But this raises a puzzle.
11:48I just described male and female roughly in terms of a
11:51size difference. Males are the smaller of the
11:55sex cells; females are the bigger.
11:57Why is it then that for so many animals males are the bigger
12:02ones, physically, and the more aggressive ones.
12:06This has been a puzzle that has occupied scientists for a long,
12:09long time. And we're pretty--there is now
12:13a pretty clear answer to it. And the answer goes like this.
12:18It is based on an idea by Robert Trivers called "parental
12:24investment." And what parental investment
12:27is, it's defined here as, any investment that's going to
12:31increase the offspring's chance of survival at the cost of the
12:36parent's ability to invest in other offspring.
12:40So, for example, suppose an animal could create
12:43an offspring by blinking an eye and then the offspring would run
12:48off? That would be extremely little
12:50investment. Suppose another animal had to
12:53work for ten years, and during those ten years
12:57could not create another offspring.
12:59That would be a huge investment.
13:04Trivers points out that within a species, females typically
13:09have a much higher parental investment than males.
13:13Because females have these big sex cells, they typically
13:17incubate them internally. They carry them.
13:21If they're eggs, they might have to sit on them.
13:23And hence, each potential child is a huge cost.
13:29For males, which have the small sex cell, you don't have the
13:33same thing. For males, it might just be a
13:37few moments of copulation and that's it.
13:40If you could ask yourself, for humans, each one of you in
13:44the room, "What is the minimum effort you can do to create a
13:48child that has half your genes?" And it's apparent that the male
13:53investment, on average, is lower than the female
13:57investment. Males can choose,
13:59or might do better off in some circumstances by putting a lot
14:02of investment into their offspring, but females don't
14:05have a choice. Females, barring technological
14:09advance, have a huge investment into any offspring;
14:13not investment in the sense or hard work and effort,
14:16though there's that too. Investment in the sense that
14:20when you're--when you're pregnant with one offspring,
14:24you can't have another. What this does is it has
14:28ramifications that percolate upwards.
14:31So, it leads to different psychologies.
14:37Males--and a single male could fertilize several females,
14:41forcing some males to go mate-less and giving rise to
14:45competition to see who can mate with the most females.
14:49For females, however, females can always
14:53find mates. So, sheer numbers don't count.
14:56But there's competition to mate with the right males,
15:00those whose offspring have the best chance of surviving.
15:05The competition now explains the puzzle we started with.
15:09It explains why males are typically larger,
15:12and often why males have evolved special weapons.
15:15These special weapons evolved for fighting other males for
15:18reproductive access. It also explains something else.
15:22Females, biologically, are choosy.
15:25And so males have to compete not merely with other males to
15:30get reproductive access but also to woo females.
15:35And so often, males have evolved special
15:39displays like this , which exist only to be
15:42beautiful, only to be attractive and to attract mates.
15:47This cold evolutionary logic was captured in this cartoon,
15:54which really does sum up a hundred of mate-selection
15:59research.
16:04The logic goes like this then: difference in the size of sex
16:08cells leads to differences in typical parental investment,
16:11leading to differences in the sorts of psychological and
16:14physiological mechanisms that evolved.
16:16Okay, that's a good story. What sort of evidence is there
16:20for it? Well, it turns out this could
16:22explain some otherwise surprising things.
16:24For instance, there should be--there are some
16:27cases where the parental investment is switched,
16:30some cases where it turns out--where the males end up with
16:34more investment than the females.
16:37And it--and the theory predicts that in these cases you should
16:43get an asymmetry. So, in cases like pipefish,
16:47for instance, the male takes the eggs into a
16:50pouch and plugs them into his bloodstream.
16:53The females shoot off. They have less of an investment
16:56than the males. In this case,
16:58you would predict, as is true, the females should
17:01be larger, the females fight other females more than males
17:05fight males, and the females try to compete
17:09for the attention of the males. Recall the movie "March of the
17:13Penguins." We saw a clip from it,
17:16and this was in the context of discussing the emotions that
17:20have evolved toward our offspring.
17:22But remember the story and how both the male and the female
17:26have to go to tremendous lengths to protect the egg.
17:30And if one of them fails, the egg dies and neither one
17:34has it. You should then not even have
17:37to remember whether male penguins are much bigger than
17:41female penguins. You should realize they should
17:44not be, and in fact they aren't. They're about the same size
17:47because the parental is equal. You should be able to predict
17:51the size differences and aggression differences based on
17:54differing parental investment. So for instance,
17:58elephant seals are four times--the males are enormous.
18:04They're four times bigger than the females.
18:06And this is in large part because elephant seals compete
18:10for harems of females. It's a "winner take all."
18:13Gibbons are about the same size. And this is because gibbons are
18:17pretty monogamous; they raise children together.
18:23This illustrates something, which is, it's not always the
18:28case that male parental investment is low.
18:32There are some species, including gibbons,
18:35where it's in the male's reproductive advantage to care
18:38for the offspring. Imagine a situation,
18:41for instance, where an offspring would die if
18:44both parents didn't watch it for many years and where the effort
18:49devoted to that offspring had to be exclusive.
18:53If you focused on another family or went away,
18:55the offspring would die. In that case,
18:57you'd have equal investment. It would matter equally to the
19:01male and the female to invest in their offspring,
19:04and the cost would be the same. There's no species--it's hard
19:08to see species that have that much of an equal system,
19:12but some primates are close to it.
19:14And this raises the question then, "What about humans?"
19:17What about us? What do we know about the
19:20differences between males and females?
19:22Well, humans are a relatively polygamous species.
19:30Most cultures--most human cultures are polygamous.
19:35American culture is what they call "serial monogamy."
19:40So, we're not like some species of birds.
19:42We don't mate for life. We do a series of peer-bondings
19:45for some period of time. It could be for life,
19:48but indeed may not be and usually isn't.
19:52Males are bigger than females. Human males--the size estimates
19:56vary so much, but the average human male is
19:58about fifteen percent larger than the average human female.
20:01This suggests that there's some--there's been,
20:04in our evolutionary history, some male-male competition for
20:08access to females, which suggests,
20:11in turn, that the parental investment is not quite equal.
20:15Males have smaller testicles for their body size than
20:19chimpanzees, but larger testicles than gorillas and
20:23gibbons. And this suggests that there
20:26was some intermediate amount of competition for the capacity to
20:30create sperm. And this is relevant for a
20:33different sort of competition, which regards the impregnation
20:36of females that have multiple mates.
20:38And this suggests that over evolutionary history women were
20:41not wantonly promiscuous, but were not entirely
20:44monogamous either; so much so that it paid from an
20:47evolutionary point of view to evolve--males to evolve the
20:51capacity to produce more sperm than other males.
20:55Aggression. Males are meaner.
20:57I mean I'm summarizing here. Meaner is not a technical term.
21:00Yes, females can be meaner, but males are at least more
21:03physically violent. They're more violent in the
21:07womb, in utero; they're more violent as
21:10children, and they're more violent as adults.
21:14Again, this is not to say that you can't find violent women or
21:19non-violent men. It's just on average there is
21:23this difference. They kick more;
21:25males kick more in the uterus. As children they're more
21:30involved in play fighting and violent combat-like sports.
21:33And as adults, wherever you go you will find a
21:37prison. And wherever you go you will
21:40find that prison is mostly full of men.
21:43They are far more likely to kill one another and to harm one
21:47another. Male sex hormones,
21:49like testosterone, are not the sort of thing one
21:52would want to inject in somebody unless you want them to turn
21:56kind of mean. They increase aggressiveness,
21:59both in humans and in other primates.
22:02What about sexual choosiness? Do male humans and female
22:09humans differ in the extent to which they will favor anonymous
22:16sex? And this is relevant from an
22:19evolutionary perspective, because the parental investment
22:22theory predicts males should be more receptive to anonymous sex.
22:26Because for males, to impregnate somebody else
22:30might fortuitously lead to another offspring;
22:35it might be good for you and doesn't carry the sort of harm
22:39that females, on the other hand,
22:40have to be very picky. Because they have to choose
22:44carefully. Remember, these systems evolved
22:47before birth control and vasectomies and so on.
22:50So, what do we know cross-culturally and
22:52psychologically? Well, prostitution is a
22:56universally, or near universally, male interest.
23:02There are male prostitutes, of course, but contrary to some
23:06various fantasies and sitcoms, they cater to male customers.
23:11Pornography is a human universal.
23:14In every society, males have done some sort of
23:18depictions of naked females for the purposes of arousal.
23:23Often they carve them into trees or do sort of sculptures.
23:27One of the weirdest findings in the last decade or so is that
23:32this extends as well to monkey porn.
23:35And so, some scientists at Duke set up a situation where monkeys
23:39could pay in fruit juice, by giving up fruit juice,
23:43to look a picture either of the female's hindquarters or of a
23:47celebrity monkey, a socially dominant monkey,
23:50some sort of combination of People Magazine and
23:54Penthouse. And so, there's some interest
23:57in this even by non-human primates.
24:03What about actually preference for sexual variety?
24:06Well, you can get at this in different ways.
24:10There is what biologists describe as the "Coolidge
24:16Effect." I have this here.
24:18And the Coolidge Effect is based on President Calvin
24:21Coolidge. And it's a story about Calvin
24:23Coolidge and his wife, who were being shown around a
24:27farm separately. And the person showing around
24:30his wife pointed out that there were a lot of hens;
24:33she noticed that there were a lot of hens but only one
24:36rooster. And she asked the guy showing
24:38her around, "Is one rooster enough?"
24:40And the guys said, "Well, you know,
24:42the rooster works very hard. The rooster has sex dozens of
24:45times a day." And she said,
24:46"Well, be sure to tell that to the president."
24:48The story goes, the president went around,
24:51the guy tells the story to the president.
24:54The president asks the man, "Huh.
24:56Has sex dozens of times each day.
24:58Same hen every time?" The guy says,
25:01"No, different hen every time." And he says,
25:04"Tell that to Mrs. Coolidge."
25:06Now, there are two responses to this sort of story,
25:10and they're both kind of negative.
25:13One thing is, "Well, everybody knows males
25:15prefer anonymous sex with strange women.
25:17Duh." The other response is,
25:20"That's sexist claptrap." You might think--you might be a
25:25male and say, "That's not me."
25:27You might know males and say, "The males I know are not like
25:30that." So, how do you find out?
25:32Well, there are indirect measures, such who goes to
25:35prostitutes. But there are also fairly
25:37direct measures. One fairly direct measure is
25:40you could ask people in anonymous surveys.
25:43So, in fact, I'll give you some anonymous
25:46surveys. I'm not going to ask people.
25:47And you just ask them. So, for instance,
25:50I want everybody to consider this question.
25:56How many sexual partners do you want to have in the next month?
25:59What is it--we're coming up to April.
26:02How many sexual partners do you want in April?
26:04Next two years? Take many of you through
26:10graduation. When you leave Yale,
26:12what do you want--like, "I had X sexual partners,
26:14and that's what I wanted." Or your lifetime?
26:17We get people to answer these questions.
26:20Professor Chun last year in this course had clickers,
26:24and he got people to do it. We are not so high tech,
26:28so we'll just do it in our heads.
26:30But here is the way the answers come out.
26:32Women say less than one in the next month.
26:35That doesn't mean they want less than one;
26:36that means many of them--many of them say zero,
26:40some say one and so on. One--four to five.
26:46Men--two, eight, eighteen. You can ask other questions
26:55from this population. So, you could ask,
26:58"Would you have sex with a desirable partner you have
27:01known--so somebody really desirable--for a year;
27:04women say yes, six months--unsure,
27:08week or less--no. Men [laughter]--and with men
27:14you could get a majority going to five minutes.
27:21This is all Q & A, pen and pencil sort of
27:25things. Some brave scientists have
27:28actually done experiments. And in one experiment
27:30somebody--I don't, you know, this is the sort of
27:33thing which you probably wouldn't do nowadays.
27:36This work has been done ten years ago, where they have an
27:39incredibly attractive man and an incredibly attractive woman and
27:42they approach people on campus. They're not from campus;
27:45they're actors brought in. And they go to people,
27:48to strangers, and they say,
27:49"I've been noticing you around campus.
27:51I find you very attractive. Would you go out with me
27:55tonight? Would you come over to my
27:56apartment tonight? Would you go to bed with me
27:58tonight?" The experiment you wouldn't
28:01think anybody would've done has been done, and women about--a
28:05very attractive man, over half of the women
28:08approached say, "Yeah, I will."
28:11Very few agree to this ["Would you come to my apartment
28:12tonight?"], and nobody agrees to this ["Would you go to bed with
28:14me tonight?"]. For men, the data are like
28:17this, they go up to there and then up to there .
28:26In this study, the twenty five percent of
28:30males who said "no" apologized profusely,
28:34and they said, "Oh, you know,
28:37my fiancé's in town, and [unintelligible]."
28:42What about behavior? Well, you--if we're interested
28:47in sex differences, you can't actually figure out
28:52what people want, male female differences,
28:56by looking at simply at the average number of times people
28:59have sex because if males and females have different
29:02priorities, then heterosexual sex is a
29:05compromise between two groups of people with competing interests.
29:09What's a more clear reflection then is gay sex between two
29:15women or between two men, because then you get a pure
29:21reflection of sexual desire. Now, the data here tend to be
29:26very messy. Again, they're survey studies
29:29but by and large every study done tends to find a difference
29:32in the expected direction, which is that females tend to
29:36be--lesbians tend to be much more monogamous than gay men.
29:42Some studies prior to AIDS – this was many years ago –
29:46found gay men to be extremely promiscuous,
29:50often having over a hundred or over a thousand partners.
29:53You wouldn't find this sort of promiscuity in females.
29:56And a way to think about this is, what these gay men are doing
30:00is exactly what your average heterosexual man would do if he
30:05had that degree of willing females who were as willing as
30:08he was. And this all suggests that
30:11there's some sort of difference along lines expected in sexual
30:15choosiness in humans. What about sexual
30:19attractiveness? What about mate preference?
30:23What do we find attractive? Well, unlike the choosiness
30:26studies, here we actually have some pretty good cross-cultural
30:30data. So one study,
30:32for instance, was done in 10,000 people from
30:35thirty-seven countries, asking people,
30:38"Who do you want to be with?" And there are different
30:41studies, some of them asking, "Who do you want to marry?"
30:44Other studies, "Who do you want as a mate?
30:46Who do you want as a sexual partner?"
30:48And one main finding is kind of reassuring, everybody likes
30:53kindness and intelligence, or at least everybody says they
30:57like kindness and intelligence. These are valued pretty highly.
31:02But at the same time, there are sex differences.
31:05Females focus more on power and status and more on interest in
31:10investing in children. And think about that from an
31:13evolutionary point of view and it makes sense.
31:15It doesn't matter hugely, from the standpoint of
31:18reproduction, how old the man is.
31:20The difference between fifteen and twenty-five and thirty-five
31:23and forty-five may matter a lot for his status in the community,
31:27his physical strength, his lifespan but from the
31:29standpoint of his sperm it doesn't matter hugely.
31:32Later on there's a drop off and it does begin to matter,
31:35but it doesn't matter hugely. What does matter is his
31:38interest in being a good father, in protecting you from
31:42predation, from murder,
31:44from assault by other people, and in taking care of the kid.
31:48Women's brains are wired up to find males with those
31:52properties. Similarly, males focus a little
31:55bit differently. They're more interested in all
31:58of these things, but also on the ability to have
32:01children. So, from an evolutionary point
32:03of view, there's actually a very big difference between a
32:06twenty-year old and a fifty-year old,
32:08from a male standpoint looking at a female, because the one can
32:11have offspring and the other cannot.
32:13So, this is a difference. But what I want to focus more
32:18on right now is back to another similarity.
32:21Everybody likes beauty. And I want to devote a little
32:27bit of this lecture to talking about physical beauty.
32:30Physical beauty, as these beautiful people say,
32:34is a curse. So she--she's like a big model,
32:38a supermodel, maybe even a
32:40super-supermodel--points out the arbitrariness of finding her
32:45devastatingly beautiful. Famous actor points out how
32:49frustrating it is that people only ignore his accomplishments
32:52and focus merely on his physical beauty.
32:55This is very frustrating. So what is beauty?
33:00What does this mean we say we find--you know,
33:04yeah, they really are very attractive people.
33:08What is it about that that makes you look and say,
33:11"Yeah, that makes sense?" Well, we kind of know the
33:14answer. We know some universals.
33:16Beauty seems to signal two things.
33:19Beauty seems to signal youth--I mean, not pre-school youth,
33:27but youth like sexually mature but young.
33:33And so the cues we find beautiful are cues to that –
33:37large eyes, full lips, smooth, tight skin.
33:41Beauty signals something else. Beauty is a marker for health.
33:45And so what we find beautiful, things like the absence of
33:50deformities, clear eyes, unblemished skin,
33:53intact teeth – that's very big – and an average face.
33:59And that last part might seem a little bit strange.
34:02What would be so good about an average face?
34:05And there are different answers to that, but one answer is,
34:09an average face, on average, should be
34:11considered attractive because any sort of deformities are
34:16variations from the average. And if you average every face
34:21together, you get a face that--where nothing bad has
34:24happened to it. There's no distortion,
34:27there's no deviation. As one gets older,
34:30the face gets less symmetrical and so on.
34:34Average-ness seems to factor out all the bad things that
34:38could happen. Good theory.
34:40How do we know it's true? Well, there's a photo roster
34:44that comes--that I have access to for this class.
34:49So, I can look at each of your pictures, and I will make you a
34:53bet about who has the most beautiful face in this course.
34:56The bet is it would be all of you.
35:01Aw. Wouldn't it be funny if I
35:06shouted out somebody's name? And you know,
35:10A) I don't have the energy to do this, and B) it would
35:13probably violate four hundred different privacy laws or
35:16whatever. But if I took all those faces
35:19and morphed them together, I would get a very pretty face.
35:23And how do we know this? Well, people have done this.
35:27They've done it with--so look at the faces from here to here.
35:32And if you are like most people, you see as you're going
35:35to the right they're looking better and better and better.
35:38It's subtle, but it's actually not so subtle
35:42that babies don't notice it. The same researchers who
35:46constructed this--these face--these average Caucasian
35:49faces, male and female,
35:50have shown these faces to babies and find that babies that
35:54prefer to look at average faces--suggesting that our
35:57preference for averaging is not the product of culture but
36:01rather is to some extent hard-wired.
36:04These two people don't exist. They're computer composites.
36:09They're a heavily averaged male face and a heavily averaged
36:14female face, both from a Caucasian data sample.
36:18They don't look bad right? They're good faces.
36:21They don't cheat. So the hair,
36:23for instance, is identical--so they
36:24don't--you can't use hair cues. But they're pretty attractive.
36:28But the story of attractiveness does not end there.
36:32How do you get a better than average face?
36:35What can you do to these faces, these average faces,
36:38and make them look even better? Well, I'll have a vote.
36:42Who's prettier? Who says the one on the right?
36:46Who says the one on the left? Left is average face,
36:51and there might be variation in this class.
36:53There are definitely variations in what people favor.
36:58This is a feminized version of the average face where certain
37:02prototype features were made more feminine than average to
37:05cue this as more of a sexual object.
37:07This is more complicated.
37:21Who thinks face A is more attractive?
37:30Who thinks face B is more attractive?
37:33Okay. Most people like face B.
37:39The exception is, and this has been statistically
37:42replicated, I think, now in three labs.
37:45Face A is preferred by women who are ovulating,
37:50and the story about why is complicated and will take us
37:56beyond the scope of this class. But currently the idea is that
38:01this is a really handsome guy; he's young, he's healthy,
38:04he looks strong, good provider;
38:06this guy is really hot, and he may not be a good
38:10provider and everything, but I'm sure he has wonderful
38:14genes. So, the idea is that one should
38:17have sex with him and then have him raise the kids.
38:24We've talked so far about things, about sex and sexual
38:28attractiveness largely from a biological perspective,
38:32looking at universals. And in fact,
38:35there are some universals in what men and women have in
38:38common and what distinguishes men and women.
38:40And in some of the sex differences, particularly
38:44related to aggression and mate preference, seem to be
38:48universal. They seem to show up to some
38:51extent across every culture you look at and, hence,
38:54are likely candidates for biological adaptations.
38:57But there are other sex differences that people are
39:01aware of where the origins are far less clear.
39:05And I think that intelligent, reasonable people could
39:08disagree about this, but I am personally quite
39:11skeptical about the extent to which these reflect biology.
39:14I'll mention them to capture the debate, but the thing to
39:20keep in mind here is that biology,
39:24natural selection, is one reason why the men in
39:27this class might differ from the women in this class.
39:30But of course, there are other,
39:31social, factors. Babies are treated differently.
39:34There have been many studies where you take a baby and
39:37swaddle it in blue and describe it as a boy versus swaddle it in
39:41pink and describe it as a girl, and people treat it differently
39:44when they think it's a boy than when they think it's a girl.
39:47You're treated differently too. It matters a lot--and there's
39:53study after study suggesting, for instance,
39:56that when you send an email or a job application or a paper to
40:00a scientific journal, it matters whether it has the
40:05name John Smith on it versus the name Joan Smith.
40:10It matters because people have different expectations and
40:13different reactions to males versus females.
40:16Some if you may have firsthand experience with this if you're a
40:20man with a name that could be taken as a woman's name –
40:24friend of mine is named Lynn, and often people think he's
40:27female – or if you're a woman who has a name that could be
40:30taken as a man's name, or if you have a name
40:33sufficiently foreign to Western ears that people can't easily
40:37tell. You'll often find people
40:39saying, "Oh," people are high-fiving each other there
40:43--you'll often find some degree of surprise and some degree of
40:48people saying, "Oh my, I didn't know you were
40:51a man. Now I will treat you
40:53differently." And so, these social factors
40:56could play a role in explaining some male and female
41:00differences. Also, there are the facts of
41:03gender self-segregation. So here something very
41:06interesting happens developmentally.
41:08Males segregate with other males;
41:12females segregate with other females--for a period lasting,
41:16it depends on the culture, but say from age four to age
41:20eleven. This self-segregation might
41:24exaggerate and enhance sex differences.
41:27It might be, for instance,
41:28as Eleanor Maccoby has proposed, that boys are slightly
41:31more aggressive than girls. But then boys go into groups of
41:35boys, and that enhances and exaggerates their aggression
41:39while the girls' non-aggressive behavior is enhanced and
41:43exaggerated in different ways by them falling into girls' groups.
41:47So, what sort of differences are we talking about when we say
41:51we're not sure of their cause? Well, one difference is one in
41:55empathy. So Simon Baron-Cohen wrote a
41:58wonderful book called The Essential Difference where
42:03he argues that men are by nature less empathetic,
42:07women are by nature more empathetic, and that this is a
42:12core sex difference. So, what do you know?
42:16Well, what's the source for this?
42:17One thing is men are more violent.
42:20Simon Baron-Cohen describes violence as the ultimate
42:23act--murder as the ultimate act of a lack of empathy.
42:27There's some relationship between how much testosterone
42:32you have in your system and how social you are – more
42:37testosterone, less social.
42:39Boys tend to be less empathetic than girls, and there's some
42:43evidence, though it's not conclusive,
42:46that boys do worse than girls on social cognition theory of
42:50mind tasks. That's what I have here,
42:53though that is quite debated. And the biggest effect,
42:57which isn't debated at all, is problems with empathy,
43:02problems of social cognition, are much more frequent in men
43:07than in women. So, these disorders like
43:11autism, Asperger's Syndrome, conduct disorder and
43:14psychopathy are predominately male.
43:17And Simon Baron-Cohen suggests that--basically,
43:21he has this slogan where he says, "To be a man is to suffer
43:26from a particularly mild form of autism."
43:29That males are just socially clueless relative to women.
43:34Final bit of trivia--This is Simon Baron Cohen,
43:38who is a very famous developmental psychologist,
43:43but his cousin Sasha Baron Cohen is far more famous.
43:48Another debate is a debate concerning sex differences in
43:52the capacity for math and science.
43:54A few years ago there used to be a president of Harvard known
43:59as Larry Summers. There are so many reasons to
44:03hiss at this point. And Larry Summers is no longer
44:08president of Harvard for various reasons, but one reason was this
44:13quote, which included in his
44:15speculations about sex differences, "...in the special
44:18case of science and engineering, there are issues of intrinsic
44:21aptitude, and particularly of the variability of aptitude..."
44:25He argued, or suggested, that the under-representation
44:28of women in the sciences in academia is because of an
44:32intrinsic aptitude difference; women are, on average,
44:37less biologically predisposed to do this sort of reasoning.
44:42The variability point is that he wasn't suggesting that
44:45there's just a difference on average.
44:48In fact, he agreed that the average skills of men and women
44:51are identical. The claim is that males show
44:55more variation. This means that there are more
44:58male retarded people and more males who are just horribly bad
45:01at this, but it also means there are more male geniuses.
45:05And he suggested that this plays a role.
45:08This, as you can imagine, proved to be an extremely
45:11controversial claim, and rather than go through it
45:14– because it would take me a class to treat the pros and cons
45:18of this argument responsibly – I'm going to refer you to a
45:21wonderful debate between Steve Pinker,
45:24who was quoted earlier, and Liz Spelke who's one of the
45:28big infant cognition people. And we spoke a lot about her
45:31work earlier on in the course. And they have a wonderful
45:34debate between two of the smartest people I know on The
45:37Edge, which was done at Harvard about
45:41a year ago and is on video here .
45:44So, if you're interested in sex differences and different
45:47theories about the mechanism of sex differences,
45:50this is where you should go. Finally, and a final topic,
45:55some of us, about 98%--and the numbers are very difficult to
46:02pin down. Maybe it isn't 98%;
46:05maybe it's ninety-seven, maybe it's ninety-nine.
46:08Let's say 98% of women are sexually attracted to men.
46:14About 96% of men are sexually attracted to women.
46:20And the numbers vary and it's very difficult to estimate it
46:23properly. As you could imagine,
46:24there are all sorts of problems with this sort of research.
46:27But there's some proportion of the population that's
46:30exclusively homosexual--some proportion of the population of
46:33men who are only attracted to other men,
46:35some proportion of the population of women who are only
46:38attracted to other women. When people talk about sexual
46:42orientation here, it's important to realize we
46:45are not talking here about behavior.
46:48There are all sorts of reasons why somebody might have sex with
46:52somebody of the same sex. You know, they might be bored.
46:56You may, you know, be experimenting,
46:58be whatever. The question is,
46:59"What do you want to do?" All things being equal,
47:02what sort of person--if you could be sexually or
47:05romantically involved with any person, who would it be?
47:08And most people are heterosexual.
47:11There's a considerable amount that varies cross-culturally of
47:14people who are bisexual. But the real puzzle is
47:17exclusive homosexuality. So, why?
47:20Well, nobody knows. We know some reasons,
47:24some answers are probably not right.
47:27It is not the case, almost certainly – maybe
47:30there are some exceptions – but it is not the case that
47:33people choose their sexual orientation.
47:36I'm not going to do this in this room, but if you asked
47:39people to raise their hands as to how many people decided who
47:43to become sexually attracted to, very few people would.
47:48Part of the issue rises in the fact that people who are gay are
47:52often extremely discriminated against, and they have no wish
47:56to be gay. They might even think it's
47:59morally wrong for them to be that way.
48:00That makes it implausible that their sexual orientation is a
48:04conscious choice. What about experience after
48:09puberty? So, there is a view that keeps
48:12coming up over and over again in the literature that people who
48:16are gay have in some sense been seduced by people,
48:19by other people--or something happened to them afterwards.
48:22This seems unlikely. There are in particular the
48:26seeds of sexual orientation later on in life seem to show up
48:31quite early in life. Again, the studies are sort of
48:35suspect, but there's some reason to believe that people who are
48:39gay and people who are straight are different long before they
48:42hit puberty with regard to their sexual and romantic fantasies.
48:46You would now expect me to say, "Well, being gay and being
48:50straight is built in. It's hard-wired.
48:53None of these stories seem right.
48:55It seems to be built in." And the answer to that is,
48:59sort of. So, if you do the standard
49:01behavioral genetic tests, and you by now know how to do
49:05them--you'd look for differences between monozygotic and
49:09dizygotic twins, you'd do the adoption
49:12comparison--you know adopted siblings and biological
49:15siblings. The answer is yes,
49:17you find that there is some sort of genetic predisposition
49:21towards homosexuality. But it can't be entirely
49:27genetic. One reason why it can't be
49:31entirely genetic is, if I'm gay and I have an
49:34identical twin, the odds that my identical twin
49:38will be gay--it's about fifty percent.
49:41Those are very high odds compared to the average in the
49:44population. But if it was truly genetic,
49:47entirely genetic, what should the number be?
49:51A hundred percent – he's my clone.
49:54He should be exactly as I am. And it's not.
49:57So, we know then that some sort of experience,
50:01possibly prenatal experience, is what explains it.
50:05Why is it so – I said before this is a huge puzzle – why is
50:10it such a huge puzzle? Well, exclusive homosexuality
50:15is an evolutionary mystery. Again, do not think that this
50:20carries any moral weight to it. What it does mean though is
50:24that it doesn't seem to follow as a biological adaptation.
50:28The puzzle is not why is it that some men have sex with men.
50:34That's not a big puzzle. Maybe they have sex with men as
50:37some sort of recreational things or pair bonding or whatever.
50:39That's not the puzzle. The puzzle is why are there
50:43some men who don't want to have sex with women?
50:47Similarly, why are there some women who don't want to have sex
50:51with men? From an evolutionary adaptive
50:54standpoint, you would think that the genes that give rise to such
50:58a behavior would be weeded out because creatures with that
51:02behavior typically, putting aside modern
51:05technology, don't have offspring.
51:07And that's what makes it such a puzzle.
51:10So, your reading response for this week is "solve that
51:14puzzle." I know I said early on in the
51:17course that reading responses would be really easy and just
51:19require you reciting back things,
51:21but that proved to be too boring.
51:23So, just solve this deepest of all puzzle.
51:26The thing in brackets at the end is very important.
51:29Your account, whatever it is,
51:31should bear some relationship to the facts as discussed in
51:35lectures and readings. We have about five more minutes.
51:40Any questions or thoughts? Yes?
51:44Student: I like your leather jacket.
51:46Professor Paul Bloom: Thank you very much.
51:48She likes my leather jacket. Any questions or thoughts,
51:54just like that one? No.
51:56Yes? Student:
51:59My question's not exactly like that one, but in other animals
52:05do they--is there similar data on other species?
52:09Professor Paul Bloom: On sexual preferences?
52:11That's a very good question because certainly your answer to
52:14the origin – give me two more minutes – certainly your
52:17answer about the origin of sexual preference in humans will
52:20be informed by the question of cross-species data.
52:23What we do know is that there are many animals that engage in
52:27homosexual behavior; they engage in sex with members
52:30of their own sex. What I don't know is whether
52:32you get exclusive homosexual behavior.
52:35So, I don't know what the rate is in nonhuman primates,
52:38for instance, of primates who do not want to
52:41have sex with members of the opposite sex.
52:43Okay, I'll see you all Wednesday.

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