professor paul bloom:sex is really strange. you ask people,"what's your favorite activity?"and if you ask people, particularly college students,particularly just fresh from spring break â€“ i've seen teenmovies â€“ they'll often answer,
"sex."or some word that is synonymous with sex.but there's a kind of a puzzle about how much time we spend onsex. and it turns out there is dataon this.
so, people say sex is theirfavorite activity, but it turns out we actuallyknow how much time the average american spends on sex.and the data i'm going to follow from was summarized inthis wonderful book by james gleick:americans tell pollsters their single favorite activityis sex. in terms of enjoyability,they rank sex ahead of sports, fishing, bar-hopping,hugging and kissing, talking with the family,eating, watching television,
going on trips,planning trips, gardening, bathing,shopping, dressing, housework, dishwashing,laundry, visiting the dentist, and getting the car repaired.on the other hand, these same studies suggestedthe average time per day devoted to sex is four minutes and threeseconds. [as gleick says,]this is not much, even if the four minutesexcludes time spent flirting, dancing, ogling,cruising the boulevard,
toning up in gyms,toning up in beauty parlors, rehearsing pick up lines,showering, thinking about sex, reading about sex,doodling pornographically, looking at erotic magazines,renting videos, dreaming of sex,looking at fashion magazines, cleaning up after sex,coping with the consequences of sex,building towers or otherwise repressing, transferring,and sublimating . and i like this passage becauseit illustrates two points,
two important points.one is we don't actually spend that much time on sex.in fact, the four minutes and three seconds is an interestingnumber because when you do times studies on how much americansspend filling out tax-related forms for the irs,it's four minutes and a few seconds.but the passage also points out that regardless of the brutetime we spend on it, it is extraordinarilyimportant. everything in life follows fromit â€“ marriage,
family, children,much of aggression, much of competition,much of art and music and creative pursuits.much of everything follows from it.if we were a creature without sex, everything would bedifferent. and what's interesting is,there are creatures without sex.there are creatures that reproduce by cloning.and in fact, this basic fact about peopleâ€“ that we fall,
roughly, into males and femalesâ€“ is an evolutionary mystery. it's not clear why animals thatare somewhat large have two sexes.from a biological darwinian perspective, having two sexes isbizarre because each time you have an offspring you toss awayhalf your genes. my children only have--each ofthem have half my dna. if i were to clone,they would have all of it. and so, it's a puzzle how sexever evolved. this is not a course inevolutionary biology,
and that's not the puzzle we'regoing to be looking at today. we're going to look at a fewquestions. first, we're going to talk fromfirst a theoretical point of view and then an empirical pointof view about how males and females are different.then we're going to talk about sexual attractiveness,some research about what people find to be sexually attractive,and then we'll talk a very little bit at the end about theorigins of sexual preference: why some people are straight,others gay, others bisexual,
and others harder to classify.now, of all the topics i'm presenting, sex is one of thesort of dicey ones from an emotional point of view.these are difficult issues because sex is,by definition, an intimate part of our lives,and it matters a lot. moreover, sex is fraught withmoral implications. and since i'm talking aboutthis from, at least at the beginning, from a darwinianevolutionary perspective, i'm obliged to start off bydealing with some of the moral
consequences and moralimplications. so, for instance,many biologists â€“ all biologists i would say â€“ willhave argued that sexual behavior,sexual action, sexual desire is,to some extent, a biological adaptationexisting to spread our genes. from that perspective then,non-procreative sex â€“ including gay sex,sex with birth control, sex by post-menopausal womenâ€“ does not serve this
reproductive goal and,in some sense perhaps, is unnatural.and one might argue then, "does this mean it's wrong?"we'll also be talking about sex differences, differences betweenmen and women, for instance,in how much you want anonymous sexual encounters,differences between men and women in social intelligence,in aggression and empathy. and regardless of what youthink about these differences, whether you think they're rightor wrong or it doesn't matter,
you'll ask the question,"to what extent are they mutable?"that is, if they exist through darwinian natural selection,to what extent can we ever get rid of them?and i want to address those two issues, the issues of moralityand inevitability, from the very start.and i want to start off with--for each of them have aquote by a prominent evolutionary scholar.so, the first one is by steve pinker in how the mindworks.
and he writes, nature does not dictate what we should accept or how weshould live our lives. well into my procreating years,i am so far voluntarily childless, having squandered mybiological resources reading and writing,doing research, helping friends and students,and jogging in circles--ignoring the solemnimperative to spread my genes. by darwinian standards,i am a horrible mistake, a pathetic loser,but i am happy to be that way,
and if my genes don't like itthey can go jump in the lake.pinker's point, i think, is a reasonable one.it is true that certain things we do exist to serve thedictates of natural selection, but that doesn't make themright? if you think that something isonly right if it leads to the generation of more genes,if it leads to reproduction, then you're not going to thinkvery much about birth control. you're not going to think verymuch about any sort of
non-procreative sex.on the other hand, if you're--moreover,if you think something's wrong if it's unnatural,you're going to think much about flying in a plane orrefrigerating food or surviving a severe infection.more generally, our bodies and brains haveevolved for reproductive success, but we can use thesebrains to choose our own destinies.nothing moral necessarily follows from the facts ofbiology.
that's all i'm going to sayabout morality. but i want you to keep it inmind when we discuss different claims about what's evolved andwhat hasn't. what about inevitability?here i want to turn to richard dawkins.richard dawkins writes, if a child has had badteaching in mathematics, it is accepted that a resultingdeficiency can be remedied by extra-good teaching in thefollowing year. but any suggestion that thechild's deficiency might have a
genetic origin is likely to begreeted with something approaching despair.if it's in the genes, it is determined and nothingcan be done about it. this is pernicious nonsense onan almost astrological scale. genetic causes andenvironmental causes are in principle no different from eachother. some may be harder to reverse,others may be easy. what did genes do to deservetheir sinister, juggernaut-like reputation?why are genes thought to be so
much more fixed and inescapablein their effects than television, nuns or books.i like the nuns. and the point here is whatcauses something is logically separate from what can reverseit. and you can think of clearcases where something is plainly genetic but is fairly easilyreversed and where something is cultural and is very difficultto reverse. here's an example.my eyesight is quite poor. the reason why my eyesight isquite poor is not due to the
patriarchy, television,culture or "the man." rather, my eyesight is quitepoor due to the crappy genes mom and dad gave me.it is genetically determined if anything is.it is also fairly easy to fix. there are these machines wherethey put panes of glass in front of your eyes and help you to seebetter. more advanced machines known ascontact lenses actually stick the thing into your eyes,and at the cost of occasional infections you come to seebetter.
it's biologically caused butfairly easy to fix. on the other hand,take an example of society's treatment of the obese.it turns out when we â€“ and we'll get to this a little bitwhen we talk about sexual attractiveness â€“ how thinsomebody is or how fat they are; what you think of that isactually not particularly hard-wired.it varies a lot from culture to culture.but once it's in a culture, it is almost impossible toshake.
so, the point,there is just that genetic does not mean inevitable,and cultural does not mean easy to fix.okay. that's general background.let's start with basic sex ed. what's the difference betweenmales and females? well, don't even think penisand vagina. there are a lot of animals thathave neither one. and the difference actuallyruns deeper. by definition,when biologists talk about
this, animals that are maleshave a little sex cell, which carries genes and nothingelse â€“ sperm cells. animals that are females have abig sex cell, which has genes but also foodand a protective cover and all sorts of other stuff.typically, the little sex cell is much littler than the big sexcell. this is the only erotic picturei'm going to show you today. it's a bunch of these littlesperm circling around the egg. it's romantic.but this raises a puzzle.
i just described male andfemale roughly in terms of a size difference.males are the smaller of the sex cells;females are the bigger. why is it then that for so manyanimals males are the bigger ones, physically,and the more aggressive ones. this has been a puzzle that hasoccupied scientists for a long, long time.and we're pretty--there is now a pretty clear answer to it.and the answer goes like this. it is based on an idea byrobert trivers called "parental
investment."and what parental investment is, it's defined here as,any investment that's going to increase the offspring's chanceof survival at the cost of the parent's ability to invest inother offspring. so, for example,suppose an animal could create an offspring by blinking an eyeand then the offspring would run off?that would be extremely little investment.suppose another animal had to work for ten years,and during those ten years
could not create anotheroffspring. that would be a huge investment. trivers points out that withina species, females typically have a much higher parentalinvestment than males. because females have these bigsex cells, they typically incubate them internally.they carry them. if they're eggs,they might have to sit on them. and hence, each potential childis a huge cost. for males, which have the smallsex cell, you don't have the
same thing.for males, it might just be a few moments of copulation andthat's it. if you could ask yourself,for humans, each one of you in the room, "what is the minimumeffort you can do to create a child that has half your genes?"and it's apparent that the male investment, on average,is lower than the female investment.males can choose, or might do better off in somecircumstances by putting a lot of investment into theiroffspring, but females don't
have a choice.females, barring technological advance, have a huge investmentinto any offspring; not investment in the sense orhard work and effort, though there's that too.investment in the sense that when you're--when you'repregnant with one offspring, you can't have another.what this does is it has ramifications that percolateupwards. so, it leads to differentpsychologies. males--and a single male couldfertilize several females,
forcing some males to gomate-less and giving rise to competition to see who can matewith the most females. for females,however, females can always find mates.so, sheer numbers don't count. but there's competition to matewith the right males, those whose offspring have thebest chance of surviving. the competition now explainsthe puzzle we started with. it explains why males aretypically larger, and often why males haveevolved special weapons.
these special weapons evolvedfor fighting other males for reproductive access.it also explains something else. females, biologically,are choosy. and so males have to competenot merely with other males to get reproductive access but alsoto woo females. and so often,males have evolved special displays like this ,which exist only to be beautiful, only to be attractiveand to attract mates. this cold evolutionary logicwas captured in this cartoon,
which really does sum up ahundred of mate-selection research. the logic goes like this then:difference in the size of sex cells leads to differences intypical parental investment, leading to differences in thesorts of psychological and physiological mechanisms thatevolved. okay, that's a good story.what sort of evidence is there for it?well, it turns out this could explain some otherwisesurprising things.
for instance,there should be--there are some cases where the parentalinvestment is switched, some cases where it turnsout--where the males end up with more investment than thefemales. and it--and the theory predictsthat in these cases you should get an asymmetry.so, in cases like pipefish, for instance,the male takes the eggs into a pouch and plugs them into hisbloodstream. the females shoot off.they have less of an investment
than the males.in this case, you would predict,as is true, the females should be larger, the females fightother females more than males fight males,and the females try to compete for the attention of the males.recall the movie "march of the penguins."we saw a clip from it, and this was in the context ofdiscussing the emotions that have evolved toward ouroffspring. but remember the story and howboth the male and the female
have to go to tremendous lengthsto protect the egg. and if one of them fails,the egg dies and neither one has it.you should then not even have to remember whether malepenguins are much bigger than female penguins.you should realize they should not be, and in fact they aren't.they're about the same size because the parental is equal.you should be able to predict the size differences andaggression differences based on differing parental investment.so for instance,
elephant seals are fourtimes--the males are enormous. they're four times bigger thanthe females. and this is in large partbecause elephant seals compete for harems of females.it's a "winner take all." gibbons are about the same size.and this is because gibbons are pretty monogamous;they raise children together. this illustrates something,which is, it's not always the case that male parentalinvestment is low. there are some species,including gibbons,
where it's in the male'sreproductive advantage to care for the offspring.imagine a situation, for instance,where an offspring would die if both parents didn't watch it formany years and where the effort devoted to that offspring had tobe exclusive. if you focused on anotherfamily or went away, the offspring would die.in that case, you'd have equal investment.it would matter equally to the male and the female to invest intheir offspring,
and the cost would be the same.there's no species--it's hard to see species that have thatmuch of an equal system, but some primates are close toit. and this raises the questionthen, "what about humans?" what about us?what do we know about the differences between males andfemales? well, humans are a relativelypolygamous species. most cultures--most humancultures are polygamous. american culture is what theycall "serial monogamy."
so, we're not like some speciesof birds. we don't mate for life.we do a series of peer-bondings for some period of time.it could be for life, but indeed may not be andusually isn't. males are bigger than females.human males--the size estimates vary so much,but the average human male is about fifteen percent largerthan the average human female. this suggests that there'ssome--there's been, in our evolutionary history,some male-male competition for
access to females,which suggests, in turn, that the parentalinvestment is not quite equal. males have smaller testiclesfor their body size than chimpanzees, but largertesticles than gorillas and gibbons.and this suggests that there was some intermediate amount ofcompetition for the capacity to create sperm.and this is relevant for a different sort of competition,which regards the impregnation of females that have multiplemates.
and this suggests that overevolutionary history women were not wantonly promiscuous,but were not entirely monogamous either;so much so that it paid from an evolutionary point of view toevolve--males to evolve the capacity to produce more spermthan other males. aggression.males are meaner. i mean i'm summarizing here.meaner is not a technical term. yes, females can be meaner,but males are at least more physically violent.they're more violent in the
womb, in utero;they're more violent as children, and they're moreviolent as adults. again, this is not to say thatyou can't find violent women or non-violent men.it's just on average there is this difference.they kick more; males kick more in the uterus.as children they're more involved in play fighting andviolent combat-like sports. and as adults,wherever you go you will find a prison.and wherever you go you will
find that prison is mostly fullof men. they are far more likely tokill one another and to harm one another.male sex hormones, like testosterone,are not the sort of thing one would want to inject in somebodyunless you want them to turn kind of mean.they increase aggressiveness, both in humans and in otherprimates. what about sexual choosiness?do male humans and female humans differ in the extent towhich they will favor anonymous
sex?and this is relevant from an evolutionary perspective,because the parental investment theory predicts males should bemore receptive to anonymous sex. because for males,to impregnate somebody else might fortuitously lead toanother offspring; it might be good for you anddoesn't carry the sort of harm that females,on the other hand, have to be very picky.because they have to choose carefully.remember, these systems evolved
before birth control andvasectomies and so on. so, what do we knowcross-culturally and psychologically?well, prostitution is a universally, or nearuniversally, male interest. there are male prostitutes,of course, but contrary to some various fantasies and sitcoms,they cater to male customers. pornography is a humanuniversal. in every society,males have done some sort of depictions of naked females forthe purposes of arousal.
often they carve them intotrees or do sort of sculptures. one of the weirdest findings inthe last decade or so is that this extends as well to monkeyporn. and so, some scientists at dukeset up a situation where monkeys could pay in fruit juice,by giving up fruit juice, to look a picture either of thefemale's hindquarters or of a celebrity monkey,a socially dominant monkey, some sort of combination ofpeople magazine and penthouse.and so, there's some interest
in this even by non-humanprimates. what about actually preferencefor sexual variety? well, you can get at this indifferent ways. there is what biologistsdescribe as the "coolidge effect."i have this here. and the coolidge effect isbased on president calvin coolidge.and it's a story about calvin coolidge and his wife,who were being shown around a farm separately.and the person showing around
his wife pointed out that therewere a lot of hens; she noticed that there were alot of hens but only one rooster.and she asked the guy showing her around, "is one roosterenough?" and the guys said,"well, you know, the rooster works very hard.the rooster has sex dozens of times a day."and she said, "well, be sure to tell that tothe president." the story goes,the president went around,
the guy tells the story to thepresident. the president asks the man,"huh. has sex dozens of times eachday. same hen every time?"the guy says, "no, different hen every time."and he says, "tell that to mrs.coolidge." now, there are two responses tothis sort of story, and they're both kind ofnegative. one thing is,"well, everybody knows males
prefer anonymous sex withstrange women. duh."the other response is, "that's sexist claptrap."you might think--you might be a male and say,"that's not me." you might know males and say,"the males i know are not like that."so, how do you find out? well, there are indirectmeasures, such who goes to prostitutes.but there are also fairly direct measures.one fairly direct measure is
you could ask people inanonymous surveys. so, in fact,i'll give you some anonymous surveys.i'm not going to ask people. and you just ask them.so, for instance, i want everybody to considerthis question. how many sexual partners do youwant to have in the next month? what is it--we're coming up toapril. how many sexual partners do youwant in april? next two years?take many of you through
graduation.when you leave yale, what do you want--like,"i had x sexual partners, and that's what i wanted."or your lifetime? we get people to answer thesequestions. professor chun last year inthis course had clickers, and he got people to do it.we are not so high tech, so we'll just do it in ourheads. but here is the way the answerscome out. women say less than one in thenext month.
that doesn't mean they wantless than one; that means many of them--manyof them say zero, some say one and so on.one--four to five. men--two, eight, eighteen.you can ask other questions from this population.so, you could ask, "would you have sex with adesirable partner you have known--so somebody reallydesirable--for a year; women say yes,six months--unsure, week or less--no.men [laughter]--and with men
you could get a majority goingto five minutes. this is all q &a, pen and pencil sort of things.some brave scientists have actually done experiments.and in one experiment somebody--i don't,you know, this is the sort of thing which you probablywouldn't do nowadays. this work has been done tenyears ago, where they have an incredibly attractive man and anincredibly attractive woman and they approach people on campus.they're not from campus;
they're actors brought in.and they go to people, to strangers,and they say, "i've been noticing you aroundcampus. i find you very attractive.would you go out with me tonight?would you come over to my apartment tonight?would you go to bed with me tonight?"the experiment you wouldn't think anybody would've done hasbeen done, and women about--a very attractive man,over half of the women
approached say,"yeah, i will." very few agree to this ["wouldyou come to my apartment tonight?"], and nobody agrees tothis ["would you go to bed with me tonight?"].for men, the data are like this, they go up to there andthen up to there . in this study,the twenty five percent of males who said "no" apologizedprofusely, and they said,"oh, you know, my fiancã©'s in town,and [unintelligible]."
what about behavior?well, you--if we're interested in sex differences,you can't actually figure out what people want,male female differences, by looking at simply at theaverage number of times people have sex because if males andfemales have different priorities,then heterosexual sex is a compromise between two groups ofpeople with competing interests. what's a more clear reflectionthen is gay sex between two women or between two men,because then you get a pure
reflection of sexual desire.now, the data here tend to be very messy.again, they're survey studies but by and large every studydone tends to find a difference in the expected direction,which is that females tend to be--lesbians tend to be muchmore monogamous than gay men. some studies prior to aids â€“this was many years ago â€“ found gay men to be extremelypromiscuous, often having over a hundred orover a thousand partners. you wouldn't find this sort ofpromiscuity in females.
and a way to think about thisis, what these gay men are doing is exactly what your averageheterosexual man would do if he had that degree of willingfemales who were as willing as he was.and this all suggests that there's some sort of differencealong lines expected in sexual choosiness in humans.what about sexual attractiveness?what about mate preference? what do we find attractive?well, unlike the choosiness studies, here we actually havesome pretty good cross-cultural
data.so one study, for instance,was done in 10,000 people from thirty-seven countries,asking people, "who do you want to be with?"and there are different studies, some of them asking,"who do you want to marry?" other studies,"who do you want as a mate? who do you want as a sexualpartner?" and one main finding is kind ofreassuring, everybody likes kindness and intelligence,or at least everybody says they
like kindness and intelligence.these are valued pretty highly. but at the same time,there are sex differences. females focus more on power andstatus and more on interest in investing in children.and think about that from an evolutionary point of view andit makes sense. it doesn't matter hugely,from the standpoint of reproduction,how old the man is. the difference between fifteenand twenty-five and thirty-five and forty-five may matter a lotfor his status in the community,
his physical strength,his lifespan but from the standpoint of his sperm itdoesn't matter hugely. later on there's a drop off andit does begin to matter, but it doesn't matter hugely.what does matter is his interest in being a good father,in protecting you from predation,from murder, from assault by other people,and in taking care of the kid. women's brains are wired up tofind males with those properties.similarly, males focus a little
bit differently.they're more interested in all of these things,but also on the ability to have children.so, from an evolutionary point of view, there's actually a verybig difference between a twenty-year old and a fifty-yearold, from a male standpoint lookingat a female, because the one can have offspring and the othercannot. so, this is a difference.but what i want to focus more on right now is back to anothersimilarity.
everybody likes beauty.and i want to devote a little bit of this lecture to talkingabout physical beauty. physical beauty,as these beautiful people say, is a curse.so she--she's like a big model, a supermodel,maybe even a super-supermodel--points out thearbitrariness of finding her devastatingly beautiful.famous actor points out how frustrating it is that peopleonly ignore his accomplishments and focus merely on his physicalbeauty.
this is very frustrating.so what is beauty? what does this mean we say wefind--you know, yeah, they really are veryattractive people. what is it about that thatmakes you look and say, "yeah, that makes sense?"well, we kind of know the answer.we know some universals. beauty seems to signal twothings. beauty seems to signal youth--imean, not pre-school youth, but youth like sexually maturebut young.
and so the cues we findbeautiful are cues to that â€“ large eyes, full lips,smooth, tight skin. beauty signals something else.beauty is a marker for health. and so what we find beautiful,things like the absence of deformities, clear eyes,unblemished skin, intact teeth â€“ that's verybig â€“ and an average face. and that last part might seem alittle bit strange. what would be so good about anaverage face? and there are different answersto that, but one answer is,
an average face,on average, should be considered attractive becauseany sort of deformities are variations from the average.and if you average every face together, you get a facethat--where nothing bad has happened to it.there's no distortion, there's no deviation.as one gets older, the face gets less symmetricaland so on. average-ness seems to factorout all the bad things that could happen.good theory.
how do we know it's true?well, there's a photo roster that comes--that i have accessto for this class. so, i can look at each of yourpictures, and i will make you a bet about who has the mostbeautiful face in this course. the bet is it would be all ofyou. aw.wouldn't it be funny if i shouted out somebody's name?and you know, a) i don't have the energy todo this, and b) it would probably violate four hundreddifferent privacy laws or
whatever.but if i took all those faces and morphed them together,i would get a very pretty face. and how do we know this?well, people have done this. they've done it with--so lookat the faces from here to here. and if you are like mostpeople, you see as you're going to the right they're lookingbetter and better and better. it's subtle,but it's actually not so subtle that babies don't notice it.the same researchers who constructed this--theseface--these average caucasian
faces,male and female, have shown these faces tobabies and find that babies that prefer to look at averagefaces--suggesting that our preference for averaging is notthe product of culture but rather is to some extenthard-wired. these two people don't exist.they're computer composites. they're a heavily averaged maleface and a heavily averaged female face, both from acaucasian data sample. they don't look bad right?they're good faces.
they don't cheat.so the hair, for instance,is identical--so they don't--you can't use hair cues.but they're pretty attractive. but the story of attractivenessdoes not end there. how do you get a better thanaverage face? what can you do to these faces,these average faces, and make them look even better?well, i'll have a vote. who's prettier?who says the one on the right? who says the one on the left?left is average face,
and there might be variation inthis class. there are definitely variationsin what people favor. this is a feminized version ofthe average face where certain prototype features were mademore feminine than average to cue this as more of a sexualobject. this is more complicated. who thinks face a is moreattractive? who thinks face b is moreattractive? okay.most people like face b.
the exception is,and this has been statistically replicated, i think,now in three labs. face a is preferred by womenwho are ovulating, and the story about why iscomplicated and will take us beyond the scope of this class.but currently the idea is that this is a really handsome guy;he's young, he's healthy, he looks strong,good provider; this guy is really hot,and he may not be a good provider and everything,but i'm sure he has wonderful
genes.so, the idea is that one should have sex with him and then havehim raise the kids. we've talked so far aboutthings, about sex and sexual attractiveness largely from abiological perspective, looking at universals.and in fact, there are some universals inwhat men and women have in common and what distinguishesmen and women. and in some of the sexdifferences, particularly related to aggression and matepreference, seem to be
universal.they seem to show up to some extent across every culture youlook at and, hence, are likely candidates forbiological adaptations. but there are other sexdifferences that people are aware of where the origins arefar less clear. and i think that intelligent,reasonable people could disagree about this,but i am personally quite skeptical about the extent towhich these reflect biology. i'll mention them to capturethe debate, but the thing to
keep in mind here is thatbiology, natural selection,is one reason why the men in this class might differ from thewomen in this class. but of course,there are other, social, factors.babies are treated differently. there have been many studieswhere you take a baby and swaddle it in blue and describeit as a boy versus swaddle it in pink and describe it as a girl,and people treat it differently when they think it's a boy thanwhen they think it's a girl.
you're treated differently too.it matters a lot--and there's study after study suggesting,for instance, that when you send an email ora job application or a paper to a scientific journal,it matters whether it has the name john smith on it versus thename joan smith. it matters because people havedifferent expectations and different reactions to malesversus females. some if you may have firsthandexperience with this if you're a man with a name that could betaken as a woman's name â€“
friend of mine is named lynn,and often people think he's female â€“ or if you're a womanwho has a name that could be taken as a man's name,or if you have a name sufficiently foreign to westernears that people can't easily tell.you'll often find people saying, "oh," people arehigh-fiving each other there --you'll often find some degreeof surprise and some degree of people saying,"oh my, i didn't know you were a man.now i will treat you
differently."and so, these social factors could play a role in explainingsome male and female differences.also, there are the facts of gender self-segregation.so here something very interesting happensdevelopmentally. males segregate with othermales; females segregate with otherfemales--for a period lasting, it depends on the culture,but say from age four to age eleven.this self-segregation might
exaggerate and enhance sexdifferences. it might be,for instance, as eleanor maccoby hasproposed, that boys are slightly more aggressive than girls.but then boys go into groups of boys, and that enhances andexaggerates their aggression while the girls' non-aggressivebehavior is enhanced and exaggerated in different ways bythem falling into girls' groups. so, what sort of differencesare we talking about when we say we're not sure of their cause?well, one difference is one in
empathy.so simon baron-cohen wrote a wonderful book called theessential difference where he argues that men are by natureless empathetic, women are by nature moreempathetic, and that this is a core sex difference.so, what do you know? well, what's the source forthis? one thing is men are moreviolent. simon baron-cohen describesviolence as the ultimate act--murder as the ultimate actof a lack of empathy.
there's some relationshipbetween how much testosterone you have in your system and howsocial you are â€“ more testosterone,less social. boys tend to be less empatheticthan girls, and there's some evidence, though it's notconclusive, that boys do worse than girlson social cognition theory of mind tasks.that's what i have here, though that is quite debated.and the biggest effect, which isn't debated at all,is problems with empathy,
problems of social cognition,are much more frequent in men than in women.so, these disorders like autism, asperger's syndrome,conduct disorder and psychopathy are predominatelymale. and simon baron-cohen suggeststhat--basically, he has this slogan where hesays, "to be a man is to suffer from a particularly mild form ofautism." that males are just sociallyclueless relative to women. final bit of trivia--this issimon baron cohen,
who is a very famousdevelopmental psychologist, but his cousin sasha baroncohen is far more famous. another debate is a debateconcerning sex differences in the capacity for math andscience. a few years ago there used tobe a president of harvard known as larry summers.there are so many reasons to hiss at this point.and larry summers is no longer president of harvard for variousreasons, but one reason was this quote,which included in his
speculations about sexdifferences, "...in the special case of science and engineering,there are issues of intrinsic aptitude, and particularly ofthe variability of aptitude..." he argued, or suggested,that the under-representation of women in the sciences inacademia is because of an intrinsic aptitude difference;women are, on average, less biologically predisposedto do this sort of reasoning. the variability point is thathe wasn't suggesting that there's just a difference onaverage.
in fact, he agreed that theaverage skills of men and women are identical.the claim is that males show more variation.this means that there are more male retarded people and moremales who are just horribly bad at this, but it also means thereare more male geniuses. and he suggested that thisplays a role. this, as you can imagine,proved to be an extremely controversial claim,and rather than go through it â€“ because it would take me aclass to treat the pros and cons
of this argument responsibly â€“i'm going to refer you to a wonderful debate between stevepinker, who was quoted earlier,and liz spelke who's one of the big infant cognition people.and we spoke a lot about her work earlier on in the course.and they have a wonderful debate between two of thesmartest people i know on the edge,which was done at harvard about a year ago and is on video here. so, if you're interested in sexdifferences and different
theories about the mechanism ofsex differences, this is where you should go.finally, and a final topic, some of us, about 98%--and thenumbers are very difficult to pin down.maybe it isn't 98%; maybe it's ninety-seven,maybe it's ninety-nine. let's say 98% of women aresexually attracted to men. about 96% of men are sexuallyattracted to women. and the numbers vary and it'svery difficult to estimate it properly.as you could imagine,
there are all sorts of problemswith this sort of research. but there's some proportion ofthe population that's exclusively homosexual--someproportion of the population of men who are only attracted toother men, some proportion of thepopulation of women who are only attracted to other women.when people talk about sexual orientation here,it's important to realize we are not talking here aboutbehavior. there are all sorts of reasonswhy somebody might have sex with
somebody of the same sex.you know, they might be bored. you may, you know,be experimenting, be whatever.the question is, "what do you want to do?"all things being equal, what sort of person--if youcould be sexually or romantically involved with anyperson, who would it be? and most people areheterosexual. there's a considerable amountthat varies cross-culturally of people who are bisexual.but the real puzzle is
exclusive homosexuality.so, why? well, nobody knows.we know some reasons, some answers are probably notright. it is not the case,almost certainly â€“ maybe there are some exceptions â€“but it is not the case that people choose their sexualorientation. i'm not going to do this inthis room, but if you asked people to raise their hands asto how many people decided who to become sexually attracted to,very few people would.
part of the issue rises in thefact that people who are gay are often extremely discriminatedagainst, and they have no wish to be gay.they might even think it's morally wrong for them to bethat way. that makes it implausible thattheir sexual orientation is a conscious choice.what about experience after puberty?so, there is a view that keeps coming up over and over again inthe literature that people who are gay have in some sense beenseduced by people,
by other people--or somethinghappened to them afterwards. this seems unlikely.there are in particular the seeds of sexual orientationlater on in life seem to show up quite early in life.again, the studies are sort of suspect, but there's some reasonto believe that people who are gay and people who are straightare different long before they hit puberty with regard to theirsexual and romantic fantasies. you would now expect me to say,"well, being gay and being straight is built in.it's hard-wired.
none of these stories seemright. it seems to be built in."and the answer to that is, sort of.so, if you do the standard behavioral genetic tests,and you by now know how to do them--you'd look for differencesbetween monozygotic and dizygotic twins,you'd do the adoption comparison--you know adoptedsiblings and biological siblings.the answer is yes, you find that there is somesort of genetic predisposition
towards homosexuality.but it can't be entirely genetic.one reason why it can't be entirely genetic is,if i'm gay and i have an identical twin,the odds that my identical twin will be gay--it's about fiftypercent. those are very high oddscompared to the average in the population.but if it was truly genetic, entirely genetic,what should the number be? a hundred percent â€“ he's myclone.
he should be exactly as i am.and it's not. so, we know then that some sortof experience, possibly prenatal experience,is what explains it. why is it so â€“ i said beforethis is a huge puzzle â€“ why is it such a huge puzzle?well, exclusive homosexuality is an evolutionary mystery.again, do not think that this carries any moral weight to it.what it does mean though is that it doesn't seem to followas a biological adaptation. the puzzle is not why is itthat some men have sex with men.
that's not a big puzzle.maybe they have sex with men as some sort of recreational thingsor pair bonding or whatever. that's not the puzzle.the puzzle is why are there some men who don't want to havesex with women? similarly, why are there somewomen who don't want to have sex with men?from an evolutionary adaptive standpoint, you would think thatthe genes that give rise to such a behavior would be weeded outbecause creatures with that behavior typically,putting aside modern
technology, don't haveoffspring. and that's what makes it such apuzzle. so, your reading response forthis week is "solve that puzzle."i know i said early on in the course that reading responseswould be really easy and just require you reciting backthings, but that proved to be tooboring. so, just solve this deepest ofall puzzle. the thing in brackets at theend is very important.
your account,whatever it is, should bear some relationshipto the facts as discussed in lectures and readings.we have about five more minutes. any questions or thoughts?yes? student:i like your leather jacket. professor paul bloom:thank you very much. she likes my leather jacket.any questions or thoughts, just like that one?no. yes?student:
my question's not exactly likethat one, but in other animals do they--is there similar dataon other species? professor paul bloom: onsexual preferences? that's a very good questionbecause certainly your answer to the origin â€“ give me two moreminutes â€“ certainly your answer about the origin ofsexual preference in humans will be informed by the question ofcross-species data. what we do know is that thereare many animals that engage in homosexual behavior;they engage in sex with members
of their own sex.what i don't know is whether you get exclusive homosexualbehavior. so, i don't know what the rateis in nonhuman primates,
sexual interest,for instance,of primates who do not want to have sex with members of theopposite sex. okay, i'll see you allwednesday.