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13 Why Are People Different?: Differences 一身的恶习都是爸妈的错?

2011-3-27 13:30| 发布者: 6228975| 查看: 5558| 评论: 0|原作者: 6228975


Professor Paul Bloom: What we've been talking about so far inthe course are human universals, what everybody shares. So, we've beentalking about language, about rationality, about perception, about theemotions, about universals of development, and we've been talking aboutwhat people share. But honestly, what a lot of us are very interestedin is why we're different and the nature of these differences and theexplanation for them. And that's what we'll turn to today.
So first, we'll discuss how are people different, different theoriesabout what makes you different in a psychological way from the personsitting next to you, and then we'll review different theories about whypeople are different. And this is the class which is going to botherthe most people. It's not dualism. It's not evolution. It's thisbecause the scientific findings on human psychological differences are,to many of us, shocking and unbelievable. And I will just try topersuade you to take them seriously.
Okay. So, how are people different? Well, there's all sorts of ways.Your sexual identity--It is at the core of your being for almost all ofus whether you're male or female. How we refer to you in language, whatpronoun we use, is indexed on how we--on your--on how--whether you'remale or female and related to that though imperfectly is your sexualorientation, who you're attracted to. The question of why some of usthink of ourselves as males and others as females, and the question ofwhy some of us would ideally want to have sex with males, others withfemales, others with both, and then a few others who have harder todefine desires, is such a good question that we're going to talk aboutit after spring break while all the sexual desire has been spent andyou could focus on [laughter] on a scientific discussion of this--notthat I recommend you do that on spring break.
How happy are you? This is also such a good topic it's going to getits own class. The very last class of the semester is devoted tohappiness and the question of what makes people happy, what makespeople unhappy, and what makes people differ in their happiness. If Iasked you to rank how happy you are from a scale of 1 to 10, thenumbers would differ across this room. And there's different theoriesas to why. Your success and failure in life--This is somewhatinteresting because you could study this in more or less objectiveways. We don't have to ask people. We could look at your relationships,how they begin, how they end, your job satisfaction. We could look atyour criminal records. Some of you are going to see time. Most willnot. Some of you will get into little troubles all through your life.Some of you already have seen the inside of a police station, possiblya lineup. Others couldn't go near such a thing. What determinesthat?
And at the root of all human differences are two main factors. Andso, I want to talk about the two main interesting factors. One ispersonality. The other is intelligence. And this is what--These are thedifferences I'll talk about today first from the standpoint of how dowe characterize them, how do we explain them, and then from thestandpoint of why these differences exist in the first place.
One way to characterize personality is in terms of people's stylewith dealing with--in dealing with the world and particularly theirstyle with dealing--in dealing with other people. So, you take a simplecharacter you know of and you could talk about that person'spersonality. You could talk about it in terms of being impulsive,irresponsible, sometimes lazy, good-hearted. You could compare thatperson's personality with other people's personalities such as mycolleague who gave a talk last class. He's wonderful. He's responsibleand reliable and very kind [laughter] and different from Homer. And so,this difference is a difference in personality.
Now, when we talk about personality we're talking about somethingelse as well. We're talking about a stable trait across situations andtime. So, if all of a sudden the person next to you kind of smacks youin the head, you might be angry but we wouldn't call that "personality"because that's something that's a result of a situation. We'd all feelthat way in that situation. It's "personality" if you walk around allthe time angry. That'd be a stable trait. That'd be something you carryaround with you and that's what we mean by personality.
Now, how do we scientifically characterize differences inpersonality? And it's a deep question. There's been a lot of attemptsto do so. Any assessment has--Any good assessment has to satisfy twoconditions. And these are terms which are going to show up all overpsychological research but it's particularly relevant for this sort ofmeasure. One is "reliability." Reliability means there is notmeasurement error. And one crude way to think about reliability is, atest is reliable if you test the same person at different times and youget the same result. My bathroom scale is reliable if whenever I standon it, it gives me more or less the same number. It's not reliable ifit's off by ten pounds in the course of a day. Similarly, if I give youa personality test now and it says that you're anxious and defensive,well--and then give it to you tomorrow and it says you're calm and openminded, it's not a reliable test. So, reliable is something you couldtrust over time.
"Validity" is something different. Validity is that your testmeasures what it's supposed to measure. So, validity means it's sort ofa good test. Forget about how reliable it is. Does it tap what you'reinterested in? So, for example, suppose I determine your intelligenceby the date of your birth. I figure out what day you were born and Ihave a theory that, from that, predicts how smart you are. That's myintelligence test, the date of your birth. Maybe people born in Januaryare the dumbest, people born in December are the smartest. Is that--Iwas born on Christmas Eve. [laughter] Is that a reliable test? Yes,it's a wonderfully reliable test. I'll test you today; I'll test youtomorrow; I'll test you next year; I'll test you the day you die; I'llget the same IQ score. Is it a valid test? It's a joke. It's absolutelynot a valid test. It has nothing to do with intelligence. But younoticed these are two different things. Something can be reliable butnot valid and something can be valid and not reliable.
Now, there are no shortage of personality tests. You could get themall over the place including on the web. So, I took one recently. Itook "which super hero are you?" [laughter] And it's a series ofquestions determining what super hero you are. You could take thisyourself if you want to. The same web page, by the way, offers you atest in whether you're "hot" or not. We'll discuss that later. And whenI did this [laughter] it told me I was Batman [laughter] and "you aredark, love gadgets, and have vowed to help the innocent not suffer thepain you have endured." Now, the honest-- [laughter] Now, to be honestthough, it's neither reliable nor valid. When I first did the test Icame up as "The Incredible Hulk." I then changed my answers a bit andwas "Wonder Woman." [laughter] And finally, out of frustration, Icarefully tailored my answers so I would be Batman. But the fact that Ican do that, well, raises questions about both the reliability of thismeasure and its validity.
Here is an example – a real world example. This is, in black andwhite form, a version of the Rorschach test, the Rorschach inkblottest. How many people have heard of the Rorschach test? Okay. Is thereanybody here who has actually, in any sort of situation, taken aRorschach test? Some people scattered in the room have taken them. Itwas originally used only for psychiatric cases but then becameextremely common. About eighty percent of clinical psychologists claimto use it and most graduate programs in the American PsychologicalAssociation who are accredited teach it. Catholic seminaries use it forpeople who want to join the seminary.
It was invented by a guy named Herman Rorschach. He devoted hisentire life to the inkblot test. His nickname when he was a teenager –I am not kidding you – was "Inkblot." [laughter] And the idea is bylooking at these inkblots and then seeing what somebody says you getgreat insights into the nature of their personality, into what theyare. Anybody want to try it? Come on. Yes. What do you see?
Student: I see two people holding hands pressed together.
Professor Paul Bloom: Two people holding hands pressedtogether. Very good. Anybody have a different reading? Yes, in back.Yes. Yes.
Student: Dancing bears.
Professor Paul Bloom: Dancing bears. Okay. Good.[laughter]Good. Okay. I got to write your name down-- [laughs][laughter] reportyou to health-- No. Dancing bears, very good. Anybody else? One other.Yes.
Student: A man in a ski mask.
Professor Paul Bloom: A man in a ski mask. Well, it turns outthat there are right answers and wrong answers to the Rorschach test.According to the test, and this is from a real Rorschach test, "it isimportant to see the blot as two human figures, usually females orclowns." Good work over there. "If you don't, it's seen as a sign youhave problems relating to people." [laughter] If you want to go for "acave entrance" or "butterfly" or "vagina," that's also okay.[laughter]
Now, the Rorschach test is transcendently useless. It has beenstudied and explored and it is as useless as throwing dice. It is asuseless as tea leaves. Nonetheless, people love it and it's used allover the place. It is used for example in child custody cases. If youhave broken up with your partner and you guys are quarreling over whogets to keep the kids, you might find yourself in a shrink's officelooking at this. And in fact, this is why they end up on the web. Thereare services. There are people who have been kind enough to put on theweb these inkblots, including the right answers to them. But they areworthless as psychological measures.
Can we do better? Well, we probably can. Gordon Allport did a studywhere he went through the dictionary and took all of the traits that hebelieved to be related to personality and he got eighteen thousand ofthem. But what was interesting was they weren't necessarily independenttraits. So, the traits like "friendly, sociable, welcoming,warm-hearted" seemed to all tap the same thing. So, Cattell and manyothers tried to narrow it down, tried to ask the question, "In how manyways are people's personalities different from one another?" How manyparameters of difference do you need? How many numbers can I give youthat would narrow you in and say what personality you are?
One approach was from Eysenck, who claimed there were just two. Youcould be somewhere on the scale of introverted-extroverted, andsomewhere on the scale of neurotic and stable. And since there'sbasically two types of traits with two settings for each, there arebasically four types of people. Later on he added another trait whichhe described as "psychoticism versus non-psychoticism" that crudelymeant whether you're aggressive or empathetic. And then you have threetraits with two settings each giving you eight types of people. Lateron Cattell dropped it down into sixteen factors. So, these sixteenpersonality factors are sixteen ways people would differ. And so, if Iasked you to describe your roommate along these sixteen dimensions, youshould be able to do so.
More recently, people have come to the conclusion that two or threeis too few, but sixteen might be too many. And there's a psychologicalconsensus on what's been known as "The Big Five." And "The Big Five"personality factors are these, and what this means is when we talkabout each other and use adjectives, the claim is we could do so inthousands of different ways, but deep down we're talking about one ofthese five dimensions. This means that when a psychological testmeasures something about somebody, about their personality, if it's agood test it's measuring one of these five things. And it means that,as people interacting with one another in the world, these are the fivethings that we're interested in. So, one of them is "neurotic versusstable." Is somebody sort of nutty and worrying or are they calm?"Extrovert versus introvert." "Open to experience versus closed toexperience." "Agreeable," which is courteous, friendly versus nonagreeable, rude, selfish. And "conscientious versus not conscientious,"careful versus careless, reliable versus undependable. A good way tothink about these things is in terms of the word "ocean," o-c-e-a-n.The first letter captures openness, conscientiousness, extroversion,agreeableness, and neuroticism. And the claim is those are thefour--the five fundamental ways in which people differ from oneanother.
Well, why should we believe this? Why should we take this theoryseriously? Well, there's actually some evidence for it. It seems tohave some reliability in that it's stable over time. So, if you testpeople over years--If I test your personality now on the five traitsand test you five years from now, it will not have changed much. Andonce you pass the age of thirty, it's very stable indeed. If you thinkabout your parents and then give Mom and Dad a mental test on wherethey stand on each of the five traits, ten years from now Mom and Dadwill still be there. It also seems to get agreement across multipleobservers. So, if I ask for each of their five traits--If I ask yourroommate what he or she thinks of you, then I ask your professor whathe or she thinks of you and your mom what he or--what she thinks ofyou, [laughter] how would--back to gender--How would they match up?They tend to overlap a lot. You walk around and you leave--and yourpersonality leaves a trail in the minds of people around you. And thistrail is characterized in terms of these five dimensions.
Finally, it seems to be--predict real-world behavior. If this didn'thave anything to do with the real world, you wouldn't be very happycalling it valid, you wouldn't take it seriously as a test, but itdoes. So, conscientiousness--how you score on a conscientious scale,relates to how faithful you are to your spouse. How openness--open youare on a psychological personality test relates to how likely you areto change your job. "Extroverts" look people in the eye more and havemore sexual partners because they're extroverts. So, these are realscales. The "Batman, Hulk, Wonder Woman" doesn't correspond to anythingin the real world, but where you stand on each of these five dimensionsdoes seem to capture it.
As an example of the agreement, by the way, somebody did a study ofseveral of the characters on the television show "The Simpsons" becausethey wanted to find characters which everybody knew. And they hadthirteen subjects judge these Simpson characters on each of the fivedimensions. These is "openness, neuroticism, conscientiousness, andextroversion" and they found considerable agreement. And this isn'tactually--What I've covered up [on the slide] is the "agreeableness."So, for those of you who have never seen the television show, this isall going to be confusing, but those of you who have, can you guesswhich characters would be particularly agreeable? Anybody guess.Yeah.
Student: Flanders
Professor Paul Bloom: Flanders. You are right. The mostagreeable people are Flanders and Marge. Who would not soagreeable?
Student: Krusty
Professor Paul Bloom: Krusty is actually--Krusty is acomplicated case [laughter] but Mr. Burns--but also--Where is he? Oh,he's not--Nelson, where's Nelson? Anyway, there's Nelson. You getstrong consensus that Ned Flanders and Marge Simpson are highlyagreeable people, 6.27 and 5.46, while Mr. Burns and Nelson are verylow. Nelson's the little kid that when trouble happens he goes, "Haha." And that's a psychological sign for low agreeability.[laughter]
Okay. That's all I want to say at this point about personality andhow we measure it and, again, we're going to get back to it later whenwe talk about differences in personality. Now, I want to deal with thesecond big difference. The second big difference is intelligence. Now,how do you define intelligence? There's no easy definition. Likepersonality, it's kind of difficult to get your fingers on what we'retalking about here. In one survey they asked 1,000 experts to defineintelligence. And some answers showed up over and over again. So, justabout everybody said intelligence involves abstract reasoning, problemsolving, and the capacity to acquire knowledge. That's at the core ofbeing smart. Other people mentioned things like memory, mental speed,language, math, mental speed again, knowledge, and creativity also ashallmarks for intelligence. And again, it might be difficult to defineit but you have a gut feeling about what it is.
So, you know Homer is actually--and this is part of the show--isactually of limited intelligence. My colleague is of very highintelligence, a wonderful fellow, [laughter] but he's probably not assmart as that guy [pointing to a picture of Einstein] who is really,really smart. And this guy, Ralph Wiggum, is particularly stupid.[laughter] And so you have a range. And it's important to figure outhow to characterize it; this is what research does, but there's a gutfeeling that there are some people who are smart and other people whoare very smart and some people who are dumb and others who are verydumb. What you want to do, from a scientific standpoint, ischaracterize this in a more robust and interesting fashion. And thetextbook has a nice review of the history of attempts to define andmeasure intelligence, but there is a couple of ideas I want to focuson.
One is an idea developed by Spearman, which is there's two types ofintelligence. There is "G" and there is "S." "S" is your ability onspecific tests. So, if there is ten tests that you're given as part ofan IQ test, ten subtests, you'll get a different score on each of thesubtests. There'll be a math test and a reading test and a spatial testand you'll get different scores. "G" refers to a general intelligence.And the general intelligence is something you bring to each of thetests in common. So, this is diagrammed here. You have these six tests.For each of them there is an "S" and then above that there is a"G."
Now, "G" is a very important notion. The term "G" is used bypsychologists a lot even in casual conversation. People say, "So, whatdo you think of him?" "I think he is high 'G.'" And what you mean ishe's a smart guy. Why do you need "G?" Well, you wouldn't need "G" ifyour performance on each of these tests had nothing to do with eachother. If the tests were genuinely separate, there'd be no generalintelligence. But what people find over and over again is that when itcomes to explaining people's performance on multiple intellectualtasks, there's two things going on. There's how good there is--they areon the specific task, but then there's also a sort of generalcorrelation that people bring to the tasks.
And I could express this with an athletic analogy. Imagine I'mrunning a gym and we have all of these different athletic tests. So, wehave a running test, we have a basketball shooting test, a swimmingtest, fencing, a list of ten of them. Now, each of you go through eachof the tests and then you'll each get ten scores. But what we'lldiscover is that the scores are not independent of one another. Peoplewho are good at one athletic thing tend to be good at another. Ifthere's somebody who's really good at running and swimming, odds arethey're probably pretty good at climbing. And the same thing holds forIQ, which is above and beyond how good people are at specific thingsthere seems to be a factor as to how well they are in general. And thisfactor is known as "G."
Now, there's, again, an extensive history of modern intelligencetests and what's really interesting is the tests now. What you need toknow about the modern tests, the Wechsler test for both adults andchildren, is how they're scored. The way they are scored is that 100 isaverage. So, it's just automatic. Whatever the average is is 100. It'sas if I did the Midterm--graded the Midterm, computed the average, gaveeverybody who got the average 100, said your score is 100. It's justthe average. It works on the normal curve and what this means is thatit works so that the majority, 68%, get between 85 and 115 on their IQtest. The vast majority, 95%, get between 70 and 130. If you are, say,above 145 IQ, which I imagine some people in the room are, you belongto 0.13% of the population. That's the way IQ tests work.
Now, this is about IQ tests. We could now ask about theirreliability and their validity. What do they mean? Well, this hasturned out to be a matter of extreme debate. This [slide] justreiterates what I just said. A lot of the debate was spawned by thebook by Herrnstein and Murray about--called The Bell Curve. Andin The Bell Curve these authors made the argument that IQmatters immensely for everyday life and that people's status in society– how rich they are and how successful they are – follows from their IQas measured in standard IQ tests. Now, this book made a lot of claimsand it's probably before many of you--many of your time, but spawnedhuge controversy. And as a result of this controversy some interestingpapers came out.
One response to the Herrnstein and Murray book was by the AmericanPsychological Association, which put together a group of fifty leadingresearchers in intelligence to write a report on what they thoughtabout intelligence--what they thought about, "Does IQ matter? How doesIQ relate to intelligence? How does--what's the different--why arepeople different in intelligence? Why do different human groups differin intelligence?" and so on. At the same time, there was also anothergroup of IQ researchers, not quite the same as the first group, gottogether and wrote another report. And if you're interested in this,the links to the reports are on the Power Point slide.
Well, what did they conclude? The conclusions were slightlydifferent but here's the broad consensus by the experts regarding theimportance of IQ tests. And the claim is IQ is strongly related moreso--probably more so than any other single measurable human trait tomany important educational, occupational, economic, and socialoutcomes. In some cases, the correlation is very strong such as successin school and success in military training. In other cases, it'smoderate but robust such as "social competence." And in other casesit's smaller but consistent, "law abidingness," and they concludewhatever IQ test measure it is of great practical and socialimportance.
So, IQ matters. More particularly, IQ matters for "socialachievement," for "prestigious positions," and for "on the jobperformance" and other work-related variables. If I know your IQ score,I know something about you that matters. It's not irrelevant just as ifI know your score on a personality test of The Big Five I would knowsomething about you that actually would tell me something interestingabout you in the real world.
On the other hand, there's a lot of controversy about why thisconnection exists. So, to some extent, people have worried that theeffectiveness of IQ is a self-fulfilling prophecy. And here is why. Ifsociety takes IQ tests important--seriously, they become important. So,it's true that your IQ is very related to your success in getting intoa good school like Yale. But the reason for this, in large extent, isbecause to get to Yale they give you an IQ test, the SAT. So, the samefor graduate school. There is the GRE, which is yet another IQ test.So, to some extent, it's a self-fulfilling prophecy. I couldmake--Society could choose to make how tall you are extremely importantfor educational success. They could say nobody under six feet tall getsinto Yale. And then some psych professor would stand up and say, "Ofcourse, height is profoundly related to educational accomplishment,"and it would be because people made it so.
So, to some extent, the society that draws highly on IQ testsregarding promotion and educational achievement and military status andso on--it's just going to follow that IQ then becomes important. At thesame time, however, the role of IQ is pretty clearly not entirely asocial construction. There is some evidence that your IQ score relatesto intelligence in an interesting sense including domains like mentalspeed and memory span. So, your score on an IQ test, for instance, isto some extent related to how fast you could think and your memoryabilities.
Now, I want to shift to the second half of the class and talk aboutwhy. So, we talked about two differences, one in "personality", one"intelligence." I want to talk about why people differ but before I do,do people have any questions? Yes.
Student: About personality--This morning I took a test--Theway the test was, they asked you 100 questions and [inaudible]
Professor Paul Bloom: It's a good question. The question isthis young man took--just took a personality test. He was accepted intoSlytherin, which is a Hogwarts reference. I'm hip to that [laughter]and--but the question is a good one. You're a clever man, high "G," andyou wanted to be in Slytherin. How do we know you didn't work the test?You're going to get these personality tests all the time and thepersonality tests--You're applying for a business and one of the testssays "I like to steal from my bosses." Well, I don't think so. No.That's a little IQ test right there. So, the question is how do youavoid that problem? The test constructors have done so in certainclever ways. For instance, there are often catch questions designed tocatch a liar. Some of these questions pose very unrealistic phenomenaso you might have a question in there saying "I have never doneanything I am ashamed of." Now, some people will say, "Yes, that's trueof me," but they tend to be liars. And so, unrealistic questions tendto catch liars.
Also, you get the same question asked in different ways across theone hundred items and they could use the correlations to figure thesethings out. Again, the proof is sort of in the pudding. The reliabilityand validity of a test is determined, in part, by just how well it doesat predicting your future performance on the test and your real worldperformance. And a test that is easily fooled--easily tricked by smartpeople wouldn't survive long as a personality test. So, we know thetest you got is a pretty good test because it seems to work for mostpeople. Yes.
Student: [inaudible]
Professor Paul Bloom: It's a good question. The question wasabout "Emotional IQ," which is something I'm actually going to touchupon a little bit later in the course, but people have talked aboutdifferent forms of intelligence. And emotional intelligence, socialintelligence, is arguably a candidate for success across differentdomains. The evidence for its predictive power is not as strong as forregular IQ tests so you might be right. It might turn out to be a muchbetter predictor but one, it's not clear that we know that yet. PeterSalovey has actually done some very interesting research on this and iscontinuing work along those lines. The second thing is emotionalintelligence is actually related to good, old-fashioned intelligence.They kind of pull together a lot. So, it's not entirely separate butthat's a good point and I'd like to return to it a little bit later onin the course. Yes.
Student: [inaudible]
Professor Paul Bloom: Good question. How do you determinewhen--what a good test is? And again, it's a real art going through thedetails of how to do that but the broad answers involve reliability andvalidity. It's a good test if I test you today and I test you tomorrowand I get the same score. It's a really good test if your score on thattest predicts your grades or, if it's a personality test, predicts howmany girlfriends you have or predicts whether people think you're anice guy. So, you have to see both the replicability of the test overtime but also its relationship to real world phenomena. And that'simportant, again. Why do we know the Batman, Wonder Woman, Hulk test isa bad one? Well, one answer is because what I--how I score on that testisn't going to tell you anything about me. It's not going to relate tomy grades. It's not going to relate to how well I'm liked. How do weknow the SAT is useful? Well, it actually corresponds with other thingslike grades. Yes, in back.
Student: [inaudible]
Professor Paul Bloom: Absolutely. The question is--When I'mtalking about personality I'm defining it in terms of something whichis stable over time. And your question, which is a good one, is, "Howdo we know it's stable over time?" Can't it change? And the answer is"yeah." A lot of personality does change over time. A personality testyou give to a ten-year-old will relate but not so strongly with thatindividual when he's fifty. On the other hand, we know that thepsychological claim that there exists such a thing as personality andit is stable over time. It's supported by the fact that if you're anextrovert now you'll likely be an extrovert twenty years from now. Notperfectly, so you're right. You could change. You could become anintrovert, you could become more of an extrovert, but wherever youstand now is significantly related to where you'll be in the future.And that justifies talking about it as a stable trait. Same with IQ.Your IQ might change. It might go up, it might go down, but it won't goup and go down that much and this is why it makes sense to talk aboutintelligence as a more or less stable trait.
Okay. Why are we different? Well, you're different because of twothings: Your genes and your environment, your nature and your nurture,your heredity and your experience. And this doesn't say anything. Thisis just defining the question. But the question of the role of genesand the role of environment in explaining human differences is aninteresting one and it could be explored in different ways.
But before talking about it I have to clear up a commonmisconception. I'm going to talk about the effects of genes and I'mgoing to talk about heredity but I want to be clear. I am talking aboutthe role of genes and also the role of environment in explaining humandifferences, not in explaining human characteristics. So, thedistinction is we're interested in the amount of variation due togenetic differences, not the proportion of an individual's trait that'sdue to genes.
So for instance, you could pull these apart. The question of--Whenwe ask what's the role of genes, what's the role of heredity in howtall people are, the question is not asking for you--what is the roleof your genes in determining how tall you are? It's not clear that'seven a sensible question. The question is there's a height differencebetween you and me and him and her. How do we explain that difference?And I could illustrate why heredity doesn't mean the same thing as thecontribution of the genes. Height is reasonably heritable, meaning thedifferences between people in the population and how tall they are isdue in large part, not entirely, but in large part to their genes.
What about the number of legs people have? Well, the number of legspeople have from zero, one or two, is actually not very heritable atall because almost everybody has two legs and people who have fewerthan two legs typically have lost one or both legs in an accident. It'snot due to their genes. So, of course, whether or not you have legs isa very genetic matter but the differences in number of legs is notusually genetic. And so, heredity is a claim about differences, not aclaim about the origin of any specific trait.
Well, now we--That's what heredity, which is genetic--Now, we couldtalk about environment. And we could break up environment into twosorts of environment. One is shared environment. And shared environmentis the extent to which the differences are caused by things--byphenomena that people raised in the same household share. So ifone--Suppose some of you are neurotic. And suppose we want to say partof that's due to your environment. Well, suppose you're neuroticbecause you have lousy parents. That would be part of your sharedenvironment because presumably siblings raised in the same householdwould have the same lousy parents.
This is contrasted with non-shared environment, which is everythingelse. Suppose I think you're neurotic because when you were five yearsold somebody threw a snowball at you and it bounced off your head.That's non-shared environment. Suppose you're neurotic because you wonthe lottery when you were twenty-one and all the money messed you up.That'd be non-shared environment.
So, what you have here is heredity, shared environment andnon-shared environment, and this equals one. That's everything.Non-shared environment is a sort of garbage can category that includeseverything that's not heredity and not shared environment. Suppose youthink you're neurotic because aliens from the planet Pluto are zappingyour brain. Suppose you're right. Well, that would be non-sharedenvironment because they're, presumably, not necessarily zapping yoursiblings' brains. Everything else is non-shared environment.
It becomes interesting to ask, for all of these differences, thephysical differences like height, but psychological differences likepersonality and intelligence, how do we parcel it out into what'sgenetic and what's environmental? This proves to be really difficult inthe real world because in the real world it's hard to pull apart genesand environments. So, you and me will have different personalities.Why? Well, we were raised by different parents and we have differentgenes. We can't tell--My brother and me might share all sorts of thingsin common but we have the same parents and the same genes, fiftypercent of the same genes. So how do we tell what's causing us to bealike?
So to do--to pull these things apart you need to be clever. You needto use the tools of behavioral genetics. And to use these tools youhave to exploit certain regularities about genes and about environment.One thing is this. Some people are clones. Monozygotic twins aregenetic duplicates. They share one hundred percent of the same genes.That's kind of interesting. Dizygotic twins are not clones. They sharefifty/fifty. They are just like regular siblings. And adopted siblingshave no special genetic overlap. That's zero percent above and beyondrandomness. Those three groups then become rather interestingparticularly when we keep in mind that by definition two people raisedin the same house by the same parents have one hundred percent the sameshared environment.
So now, we can start to answer these questions. Suppose you findthat monozygotic twins are much more similar than dizygotic twins.Well, that would suggest that there's a large role of genes in thosetraits that you're interested in. It would not cinch the matter becausethere are other factors at work. For instance, monozygotic twins lookmore alike than dizygotic twins and maybe they have different and--theyhave more similar environments because of this similarity inappearance.
Are monozygotic twins just as similar as dizygotic twins? If so,then it would show that that extra overlap in genes doesn't reallymatter. And so, it would suggest a low role of heredity. Are adoptedchildren highly similar to their brothers and sisters? If so, thenthere's a high role of shared environment. Suppose the Bloom children,and there are seven of them, all have an IQ of 104 and we adopt threekids and then at the end of the day those three kids each have an IQ of104. That would suggest that--And we do this over and over again acrossdifferent families. That would suggest that there's something about theBloom family being raised by me that gives you an IQ of 104. On theother hand, if the IQ of the adopted kids had no relationship to thoseof the biological Bloom children, it would suggest that being raised byme has no effects really on your IQ. It's sort of separate.
A separate--A second--A final contrast, which is the thing thatpsychologists love, is identical twins reared apart. That's the goldstandard because you have these people who are clones but they'reraised in different families. And to the extent that they are similarthis suggests it's a similarity of their genes. And in fact, one of themost surprising findings in behavioral genetics--The caption here [acartoon on a slide] is "Separated at Birth, the Mallifert Twins MeetAccidentally." [The cartoon twins] ended up at a patent office with thesame device. One of the hugely surprising findings from behavioralgenetics is how alike identical twins reared apart are. They seem tohave similar attitudes to the death penalty, to religion and to modernmusic. They have similar rates of behavior in crime, gambling anddivorce. They often have been found to have bizarre similarities. Theymeet after being separated at birth and they meet at age thirty andthen it turns out that they both get in to a lot of trouble becausethey pretend to sneeze in elevators. There was one pair of twinsstudied by behavioral genetics who were known as the "Giggle Twins"because they were--both would always giggle, they'd burst into gigglesat every moment even though it couldn't be environment because theyweren't raised together.
More objectively, the brain scans of identical twins reared apartshow that their brains are so similar in many cases you can't tellwhose brain is who. I could tell your brain from my brain from a brainscan and my brother's brain from my brain from a brain scan. But if Iwere to have an identical twin it would be very difficult to tell whosebrain is whose even if we had no environment in common.
So, this leads to two surprising findings of behavioral genetics.This is the first one. There is high heritability for almosteverything. For intelligence, for personality, for how happy you are,for how religious you are, for your political orientation, there--foryour sexual orientation, there is high heritability. There's a higheffect of genes for just about everything.
Now, that's actually not the controversial thing I'm going to tellyou. But before getting to the more controversial thing I want to raiseanother issue which often gets discussed and has a good treatment inthe textbook. This suggests that individual differences withinthis--within a group have genetic causes. Does that mean that groupdifferences are largely the result of genetic causes? So, we know thatthere are clear differences in IQ scores among American racial groups,between whites and Asians, African Americans, Ashkenazi Jews. There'sclear and reliable IQ differences as well as some otherdifferences.
Now, to some extent, these groups are partially sociallyconstructed. And what this means is that whether or not you fall into agroup it's not entirely determined by your genetic makeup. It's oftendetermined by social decisions. So, whether or not you count as a Jew,for instance, depends not entirely on genetic factors but also onfactors such as whether you're reform or orthodox and whether you--sowhether you would accept that a child of a Jewish man and a non-Jewishwoman is Jewish. Similarly, categories like African American and whiteand Asian often overlap broad genetic categories and they don't makefully coherent genetic sense.
At the same time though, there is plainly some genetic differencesacross human groups and say with regard to vulnerability to disease.Ashkenazi Jews for instance are vulnerable to Tay-Sachs. And the factthat you could have this sort of genetic vulnerability suggests thatthere is some sort of reality to these groups. So, you have to ask thequestion now, to what extent does the high heritability in individualsmean that there has to be a heritable explanation across groups? Andthe answer is "not at all." I'm not saying that this means that there'sno genetic explanation for human group differences. All I'm saying isthe question of the phenomena of--within-group genetic differences doesnot mean that there is across-group genetic--sorry, between-groupgenetic differences.
There is a nice example by Richard Lewontin, the geneticist, wherehe imagines two plots of--what are you--some sort of wheat, yeah, twoplots of land and each one has a set of seeds and--Oh, no. They're overthere. [pointing to slide] No. Anyway, one of them you fertilize a lot.The other one you fertilize a little. Now, within each plot how muchthe seed grows is actually largely determined by the genetics of theseed. And so, you'd find high heritability for growth in the seeds. Butthe difference between groups has no genetic cause at all. It's causedby which groups you fertilize more than others.
Here's another way to do the logic. Suppose from the middle [aisleof the classroom] down here, you guys, [pointing to the people on theright] I hate you, I really hate all of you, and [pointing to thepeople on the left] I like you, so I make up two Midterms. You probablydidn't notice but there were two Midterms. This Midterm was fiercelyhard, savagely hard [pointing to the people on the right]. It took manyof you until the end of class to do it. This Midterm [to the people onthe left] was, "Which is bigger, a dog or an elephant?" [laughter]because I like you and I want you all to succeed.
So, you have two different groups, you guys and you guys. Withineach group some people are going to do better than others. Theexplanation for that might actually have to do with your genes. Itmight have to do with your environment, how much you study, but allsorts of reasons for that. Within each group some of you will do betteron the hard test than others on the hard test, some better on the easytest than others on the easy test. But how do we explain the groupdifference? Well, it has nothing to do with genes. The groupdifference, the fact that you will do much worse than you, has to dowith the exams I give. My point, again, is that there is a logicaldifference between a within-group difference, within this half of theclass, and a difference between groups, within--between this group andthis group.
What do we know about--;So, that just shows they're not the samething but what's the fact of the matter? What do we know about humandifferences between different human groups? Again, the textbook has agood discussion of this but I'm going to give two reasons from thetextbook that at least group differences are at least to a large extentdue to environmental and not genetic causes. One is that thedifferences we find in IQ seem to correspond better to socially definedgroups than genetically defined groups. They seem to correspond togroups defined in terms of how people treat you and how people thinkabout you as opposed to your DNA. And to the extent that turns out tobe true that would mean that a genetic explanation is not reasonablefor those differences.
A second factor is that we know IQ can differ radically without anygenetic differences at all. And the most dramatic evidence of that isthe Flynn effect. The Flynn effect is one of the freakier findings. TheFlynn effect is the finding that people have been getting smarter. Youare much smarter on average than your parents if--and the IQ tests hidethat. Here is why they hide that. They hide that because they alwaysmake 100 the average. So, you come home and you say, "Dad, Dad, I justdid an IQ test. I got 120." And your father says, "Good work, Son. Igot 122 when I was your age," but what neither of you acknowledge isyour test was much harder. As people got better, they had to make thetest harder and harder. And this is plotted by the Flynn effect.
[referring to a graph] One of these lines is American and one isDutch. I don't know which is which but the gist of it is that somebodywho would have--that if you in 1980 would take the 1950 test, youraverage person in 1980 would score 120 on the 1950 test. What thismeans is if you take your person who's average now and push him backthrough time twenty years, thirty years, he would do much better thanaverage. Nobody knows why people are getting smarter and there'sdifferent theories of this. And in fact, well, wait until you see yourreading response. But what this illustrates is that IQ can changedramatically over the span of a few decades without any correspondinggenetic change. And that leaves open the possibility, in fact, maybethe likelihood, that the differences we find in human groups, existinghuman groups, are caused by the same environmental effects that haveled to the Flynn effect.
Okay. This is not the surprising claim though, the high heritabilityfor almost everything. This is the surprising claim. Almost everythingthat's not genetic is due to non-shared environments. The behavioralgenetic analyses suggest that shared environment counts for little ornothing. When it comes to personality or intelligence then, an adoptedchild is no more similar to his siblings than he or she is to astranger. To put it a different way, the IQ correlation in geneticallyunrelated adults who are raised in the same family is about zero.Suppose the Bloom family all has an IQ of 104 and we adopt a kid. Whatwill this kid's--We adopt him as a baby. We raise him to be atwenty-year-old. What's his IQ? Answer? We have no idea because the IQof the Bloom family who are unrelated to him has no effect at all.
Now, if you think about the implications of it, it becomescontroversial and Newsweek, I think, caught the big issue whenthey put in their title the question "do parents matter?" And thequestion--And the issue is parents are shared environment. To sayshared environment does not affect your intelligence or yourpersonality suggests that how your parents raised you does not affectyour gene--your intelligence or your personality. This isn't to sayyour parents didn't have a big effect on your intelligence andpersonality. Your parents had a huge effect on your intelligence andyour personality, around 0.5 actually. They had this effect at themoment of conception. From then on in, they played very little role inshaping you--what you are.
The case for this which generated the Newsweek cover came upin a controversial book by Judith Harris called The NurtureAssumption which has a very long subtitle, "Why Parents Turn--WhyChildren Turn Out the Way They Do, Parents Matter Less than You Thinkand Peers Matter More." Judith Harris has had an interesting history.She was kicked out of graduate school at Harvard and told that shewouldn't amount to much. The person who wrote the letter saying thatshe was not going to amount to much was the department chair, GeorgeMiller. In 1997, she won the George Miller award for her astoundingaccomplishments. And when she wrote the book she took as a startingpoint, her point of disagreement, a famous poem by the poet PhilipLarkin and many of you have probably heard this. The poem goes likethis:
They ** you up, your mum and dad.
They may not mean to but they do.
They fill you with the faults they had
And add some extra just for you.
The last line of the poem, the last bit of the poem, ends: "Manhands on misery to man. It deepens like a coastal shelf. Get out asearly as you can and don't have any kids yourself." It's beautiful.[laughter] Harris wrote a rebuttal: "How sharper than a serpent's toothto hear your child make such a fuss. It isn't fair. It's not the truth.He's **ed up, yes, but not by us." [laughter]
Just to show that academic debates never end, a Britishpsychoanalyst named Oliver James, outraged by Judith Harris' bookThe Nurture Assumption, wrote another book in response calledThey ** You Up. [laughter] Now, how do you tell yourgrandparents, "I wrote a book." "What's it called?" "Can't tell you."[laughter]
Anyway, look. If you're paying attention, this has to sound wrong.You must be thinking of course there must be an effect of sharedenvironment. Of course parents have an effect. After all, good kidshave good parents. There is no doubt at all that this is true. There isa high correlation between parent and child for everything. If yourparents read a lot and there's a lot of books in your house, you willbecome a reader. If your parents are religious, you will be religious.If you're raised by Bonnie and Clyde, you will be a young thug.[laughter] If your parents are poor, you're likely to be poor. If yourparents are brilliant, you're likely to be brilliant. No doubt at all.It is an extremely robust correlation. But the problem is thiscorrelation could be explained in different ways. Everybody thinks it'sbecause parents do something that affects their kids. Your parents arebookish, they read to their kids, so their kids become bookish, butanother possibility, which we know is true, that almost always parentsshare their genes with their kids.
Another possibility is it's the parents who are affecting--sorry,it's the child who is affecting the parents, not vice versa, and toillustrate this, these different possibilities, I want to tell you alittle bit about a study. And I really find this a fascinating study.It was reported last year and it was a study shown that--suggestingthat family meals help teens avoid smoking, alcohol, drugs. It involveda phone questionnaire where they phoned up teenagers and their parentsand said, "Hey, teenager. Do you do a lot of drugs?" "Yes." "Do youhave dinner with your parents?" "No." And they take it off--and thenthey ask other people and they find that the kids who are the good kidshave meals with their parents, suggesting this headline.
I like this study because I have read--I must have read in my careera thousand studies and this is the worst study ever done [laughter] inthe history of science. And it's almost--We could devote a week todiscussing what's wrong with this study. Let's just--But here's theidea. It is possible that they are right. It is actuallypossible--there's no--I have no evidence against it – that having mealswith your kids makes them into good, drug-free, non-promiscuous,non-drinking kids. Of course, it's equally possible it's the other wayaround. If little Johnny is kind of--is out there smoking pot andcavorting with prostitutes and stuff like that, he's not going to comehome for the family meal. It's the other way around. While if he's agood kid, he might be more likely to have a family meal. So, thedirection--It might actually be not family meals make good kids butrather good kids stick around to have--if they have nothing better todo and have meals with Mom and Dad. [laughter]
Another possibility is there's good families and bad families. Agood family is likely to have drug-free kids and a family meal. A badfamily is likely to have stoned kids and no family meal. [laughter] So,there--maybe there's an effect of that. The parents had nothing to dowith the family meal.
Here's the even weirder part. They didn't factor out age so thinkabout this. Their sample included children ranging from twelve toseventeen but let me tell you something about twelve-year-olds.Twelve-year-olds don't use a lot of drugs and are likely to eat withtheir family. Seventeen-year-olds are stoned all the time and theydon't eat with their family. [laughter] I've just begun on this studybut the point is when you hear something like--So now, take somethingwhich you may be more likely to believe. Maybe you believe that havingparents who read to their kids, that's good for their kids. Well, maybeit is but most of these criticisms apply to that study too. A bookishkid is more likely to get his parents to read to him. A goodfamily--Parents who are good parents in general are more likely to doall sorts of good things to their kids and have good kids besides.
Take another case, the so-called cycle of violence. Yes, it's true.Parents who smack their kids tend to have statistically more violentkids. But maybe the causality goes the other way around. Maybe if youhave a kid who is a troublemaker you're more likely to smack him.Maybe, which seems to be entirely likely, the propensity for violenceis to some extent heritable. And so, even if the kid was not raised bythe smacking parent, whatever properties of that parent caused him--ledto that violence got inherited by the kid.
Now, again, this isn't going to sit right for you and I've had--Iput this down because last year when I gave this talk people ran up tome and told me this. They said, "Look. I know my mom and dad had a hugerole in my life. That's why I'm so happy and successful," then otherpeople said, "That's why I'm so miserable and screwed up," but eitherway blame it on Mom and Dad or thank Mom and Dad. And you might thinkyou know. When you become famous and you stand up and you get yourawards maybe you'll thank your mom and dad. When you go to yourtherapist and explain why you're so screwed up maybe you'll blame Dad."He never took me to a baseball game." Well, maybe, [laughter] but youdon't know. Were you adopted? If you weren't adopted, you can't evenbegin to have the conversation about how your parents messed you upbecause if you're a lot like your parents you might be a lot like yourparents because you share their genes. Of course, you resemble yourparents. Moreover, how do you figure out which is the cause and whichis the effect? "Mom smacked me a lot and that's why I turned out to besuch a rotten person." Well, maybe she smacked you because you wererotten. [laughter] I don't want to get personal but it's very difficultto pull these things apart.
A final point on this. One response to Harris' book is this. "Look.Even if this is true, you shouldn't let this get out because if parentsdon't mold their children's personalities maybe why should they treattheir kids nicely?" And you might be wondering this. You might bethinking, well, gee, if you don't have any effect on how your kids turnout, why be nice to them, but there are answers. You might want to benice to them because you love them. You might want to be nice to thembecause you want them to be happy. You might want to be nice to thembecause you want to have good relationships with them. And I have alittle bit more but I'm going to skip it and I'm going to move right toyour reading response, which is very, very simple, easy to answer, easyto grade: Explain the Flynn effect. It's a toughie so just explainthat. Okay. Have a wonderful spring break and I'll see you when you getback.
[end of transcript]
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