What Do We Know About Human Intelligence?

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Synopsis

What do we know about the science of human intelligence? Douglas Detterman, emeritus professor at Case Western Reserve University, shares what he has learned from decades of working in this field.

If you want to learn about the research that goes on in any field, there is probably no better person to ask than the founding editor of a journal who has seen almost everything. Douglas Detterman, Professor emeritus at Case Western Reserve University, is currently writing a book tentatively titled "The Science of Intelligence" surveying all that there is to know about intelligence, and he continues to serve as editor for the journal.

I had the opportunity to sit down with Doug at his home, which overlooks a quiet body of water and a landscape that is a place where many birds and other animals visit.  He’s quite soft spoken, friendly, and chooses his words carefully, and I can’t help but notice how modest he is considering how much he has contributed to our understanding of intelligence. But of course I know beneath that exterior lies a formidable intellect, one that has been surveying and working in the same field for the last four decades and has not stopped.

As Doug noted in an interview on why he does what he does every day: “It’s very much like the story told by the coal miner. The coal miner says ‘I just love the freedom of the job. I go down in the mine and do whatever I want all day long. It’s just great.  Such a wonderful job. All I have to do is bring up ten tons of coal at the end of the day.’”

In this interview we covered a wide range of topics, including the history and future of intelligence, myths about intelligence, the teaching of intelligence, as well as advice to students. Doug impressed upon me how important our understanding of intelligence may be to the future of humankind.

1. The History and Future of Intelligence Research

JON: You founded the journal Intelligence in 1977 and the International Society for Intelligence Research (ISIR) in 2000. You have been the editor of the journal and have seen every imaginable study on the topic of intelligence across nearly the last four decades. What are the most important things you can tell me about our understanding of intelligence that was different in 1977 than in 2014?

DOUG: We have come miles and miles since Intelligence first started. If you look back at the early issues of that journal, they were mostly small studies that were very limited in their statistical power and statistical application. What’s changed over the years? A huge increase in knowledge about the genetic origins or contribution to intelligence and greater statistical sophistication. The N’s have gotten substantially larger in studies now. We know more about both ends of the continuum, the high end and the low end. It’s like day and night. There’s essentially been a revolution in what we know about intelligence. We know more about the cognitive contribution to intelligence. There are three areas that I think are important to understand in the future: genetics, neuroscience, and cognition. All three of these areas have made incredible advances and are in the process of coming together and merging. I see that happening now. 

Do you think the convergence of these fields will help with any future applications?

I think it’s certain that they will. If we have a better understanding of intelligence, we’ll understand many things better, from education to mental retardation to genius and super achievement.  Intelligence is humans’ most important adaptive function. It’s related to everything you can think of: health, social problems, and so many other things. That’s just a short answer.

What have you learned from founding an academic journal and society?

I guess I could give you flip answers like “don’t do it.” I think it’s important that people have appropriate outlets to publish their work, and I don’t think there were any for this area before Intelligence. Particularly people who may have unpopular ideas, or have some ideas that are controversial in some other areas that aren’t particularly controversial. It’s good to be able to submit an article to a place where the work that you’re doing will be understood, and you don’t have to justify it in a hundred different ways. I view the society [ISIR] as having the same function as the journal.  It brings people together. It makes collaborations possible.  It allows students to see all the stuff that’s going on in this field. 

In what domains do you think intelligence has the most significance? Why?

It’s hard to pick a single domain, because it’s important in so many ways. It’s important to societies in general. If societies are to succeed, they need to make the most of the talent available to them. How to find that talent, how to encourage it, that’s an important consideration. Also they need to know when people aren’t succeeding why they aren’t succeeding and what it is about them that make it difficult for them to succeed. I began by studying intellectual disability, and such people have a difficult time and it’s important that we understand why and what can be done about it. Those are things that are important to society. But there are many things that are important to the individual, such as health care—it’s vital to understand that people with different levels of intellectual ability are going to be more or less able to navigate health care systems and do the sorts of things that they need to do to keep themselves healthy. And that’s not something that is accounted for much in current health care systems. And I think it makes a huge difference in outcomes. I think people are just starting to look at this, this area of cognitive epidemiology.  Just generally, understanding our adaptive skill of intelligence is important for the future of humankind.

What are the most exciting areas of intelligence research today that you think will hold great implications for our future? What areas do you think are the most fruitful to study?

I’m most interested in cognition, but that doesn’t mean it’s necessarily the most important area. There have been substantial advances in methodology in behavior genetics and neuroscience and I suspect that those will make important contributions in the future. The combination of those two things is going to be important to understanding how the brain works and why there are differences among people. I just went to a conference on developmental neuroscience, and it was fascinating what people are finding about the relationships between genes and all kinds of proteins in the brain that are doing different things and how they are affecting the development of the brain. I think cognition has been fortunately fairly well developed. We have pretty good tests of cognition. We have pretty good behavioral measures of what we’d like to understand at a deeper genetic and neuroscience level. And they are getting the tools to be able to do that now.

Do you think a lot of advances come through tools?

Yeah it always has been the case. Devices that allow you to measure things that you couldn’t measure before. In genetics they’ll have huge databases of total genome scans and in neuroscience they’ll have all kinds of techniques to watch the living brain in action and see what areas are activated, how things are connected.  Those kinds of techniques, which have only been available in the last ten or twenty years, are going to bear real fruit over the next twenty years.

Do you think there are large sources of data now that people can mine?

Yes. I think 23andMe has huge samples. The problem is we don’t even appreciate the power needed.  It’s going to take in the millions or tens of millions to really get accurate information on the genetic side of intelligence. What people are finding is that you think one gene does something, but there are multiple ways for the genetic architecture to produce the same effects, and what people are finding is that there are often multiple genes that can do the same thing or cause the same effect but through different routes. And so all of those are going to have to be explained. And some of them are unique mutations that only a single person has, and so it’s going to be a complicated process.

Is the evidence pretty overwhelming that intelligence comes from the brain?

Yes. I think the techniques are there. It’s just a matter of time and patience and hard work to discover how this is all related to the brain. We don’t know now how it’s related to the brain. The brain has been kind of a black box, a mystery, but I think there’s no doubt that it’s related to intelligence. We know that because of genetic defects that lower intelligence substantially, and all the other information we have about cognitive tests, how some people can do them better than others.  Probably half the genes in the body affect the brain, so it’s going to be a complicated story about how genes affect intelligence. We already know there are multiple genes, and probably none of them account for a tiny percent of the variance at most.

2. Myths about Intelligence

You’ve noted that “Much of what people know about intelligence is wrong because they learned it from the popular press.” Which of these “myths” do the public ascribe to but need to be debunked?

There are hundreds of them. For example, the idea that intelligence tests are biased. But they’re not. There are tremendous statistical techniques for finding bias in tests and everybody who makes commercial intelligence tests makes sure that their tests are not biased in a technical sense. Often items that would appear biased on their face are not actually biased in a statistical sense. And there are numerous examples where items were eliminated to keep people happy, not because they were actually biased.

Another myth is that anybody can be smart if they just work hard enough. And that’s just not true. I’ve worked with intellectually disabled people for a lot of years, and it’s unfair to say that those people just aren’t smart enough because they haven’t worked hard enough. It’s not the case.  Well it turns out that about half of intellectually disabled people have no identifiable biological cause. They’re probably at the low end of the distribution. But there will be people who through no fault of their own will not be able to achieve what you’ve achieved for instance. No matter how hard they worked they wouldn’t be able to do it. They just don’t have the intellectual capability to be able to perform at that level. What’s kind of interesting about this is that it was pointed out long ago, at the middle of the last century, about what would happen when the meritocracy emerged. And [Richard] Herrnstein was one of the first people to point it out.  I mean, it’s usually PhDs who argue this. “I’ve got a PhD, I’m not that smart, if I can do it than anyone can do it.”

Do you think people are being disingenuous when they say that?

No, I think they really believe it. And I think it’s because they’ve lived in a highly segregated community, where they’ve seen people and some of those people didn’t make it, maybe because they didn’t work hard enough.  And they figured that they worked hard. So maybe the reason for not making it is not working hard. But we live in a highly intellectually segregated world. And somebody who is in higher education seldom comes into contact with somebody who is less capable. People can be segregated pretty much from the beginning of school. I think it’s helpful to be exposed to the full range of human ability, but even in the service—I was in the Navy—you’re not exposed to the full range because they cut off the bottom ten percent. But I’ve worked with people in the whole range, and I think that has been useful to me, and I used to take students all the time to meet with intellectually disabled people. It doesn’t mean that because someone is intellectually disabled that they shouldn’t be a part of society.  I’m fond of saying that I’ve had a lot of conversations with intellectually disabled people and an equal number of conversations with university deans and overall I’ve enjoyed my conversations with intellectually disabled people more.

The practice myth is another one: the idea that it just takes 10,000 hours of practice to become an expert. It has been fairly well demolished recently in a number of papers. That’s just an extension of the idea that if anyone works hard enough they can accomplish anything. And it’s also not true because you need more specific abilities.  For example, if you want to be a musician you need to have special abilities, if you want to be an athlete you need certain abilities and genetic endowments. In fact I just read The Sports Gene by David Epstein, and one thing that book really does well is talk about the genetic by environment correlations that can exist to produce really exceptional performance.

I think it’s pretty well known that in sports talent and practice both matter, and there’s not much you can do after a certain point if everyone is practicing similarly. I’m not sure why we would think this wouldn’t translate to other areas?  Why would it just be isolated to sports?  For example in education.

Well that’s what you get in education.

Also, it seems that people don’t want to believe that we each have limits. Do you think that’s true?

I think it is true. It’s all part of the philosophy of work hard and you’ll be rewarded. That everybody is the same and the only difference is how hard you are willing to work to achieve a particular goal. And if you don’t achieve that goal it’s because you haven’t worked hard enough, not because you’re not capable enough. It would seem to me that a much smarter way of looking at things is that I’m better suited for some things than other things and so I should try to find those things I am suited for and work at those. We’re all unique and it would be odd if we were all great at everything.

You’ve published papers showing that standardized tests, such as the SAT and ACT, in fact measure general intelligence to a large degree and function as intelligence tests.  Why is this finding significant? Now that I think about it, I guess this could be one of the myths too.

Yeah it is one of the myths and it has been perpetuated by testing companies because intelligence is not in favor today. If you look at the history of these tests, they derive from the original intelligence tests, they’re clear descendants of the Army Alpha and the ASVAB and others. The SAT came directly from these tests, so it’s no wonder that they do correlate so highly with intelligence tests. But it’s also no wonder because the predictive portion of these tests is general cognitive ability, it’s g that’s carrying much of the predictive weight. However I think test companies have not wanted to be associated with that particular view, even though they were the people who developed these tests originally. For public relations reasons I think they’ve called them achievement or potential tests or whatever word you want to come up with, and have avoided using the word intelligence which is what they really measure. The first test company, Psychological Corporation, was founded by James McKeen Cattell when he was thrown out of Columbia for writing to his senator for protesting World War I on university stationary. So he lost his job and sued Columbia for getting rid of him and got a $40,000 settlement and put it into the Psychological Corporation where they started making up these psychological tests. So today Psychological Corporation is known for the WAIS and many other measures.  Testing is a huge business.

3. Teaching of Intelligence

My understanding is that there is a large gap between what is understood among intelligence researchers and what is understood among the general public regarding intelligence. Why this disconnect? Why is it important for the public to understand the research findings in the area of intelligence? You’ve written an article and brought together a special issue on the “teaching of intelligence” to college students. What are your thoughts on intelligence researchers being good educators not only to their academic colleagues and the students they teach in their classrooms but also the general public?

I think it’s critical.  And the reason I did that special issue is because there are very few courses on human intelligence being taught. And I think it has to do with how people just don’t want to particularly teach intelligence and there’s been some resistance to it.  But I think they should and this really came to light when I was asked to review a chapter on intelligence for a very well-known introduction to psychology textbook. And it was just outdated and wrong. So I criticized it thoroughly and wrote back and fortunately the author was responsive and they changed the chapter. But this is what people are getting. It’s out of date. Probably caters more to prejudice rather than fact. So I think it’s important that people know there is some place where they can get the facts about intelligence. And I think at least an introductory course on intelligence at the undergraduate and graduate level is needed. Arthur Jensen once complained to me that he once had a student tell him that in another course they were saying all kinds of crazy stuff about intelligence so Jensen agreed to give the lecture on intelligence.  This was probably twenty or so years ago. It’s gotten better since then, hopefully, but there’s still a lack of solid information about intelligence and its importance.

How do you think something like this is linked to interest in research areas over time? So neuroscience is a very hot area because this is what is what is being taught in the classrooms, and so you get a lot of people who want to enter neuroscience.

I really think intelligence is on the upswing. I think people in neuroscience and genetics are getting more and more interested in intelligence. Sometimes they make fools of themselves because they don’t know.  There’s some recent examples where people have published papers that just don’t make any sense to somebody who knows the field of intelligence well. And when those papers are commented on by somebody who does, it’s an embarrassment. They seem to think they’re going to straighten out this backwater idea about intelligence, and so they come up with these ideas that have been thought about before, and it usually ends badly for them because they don’t understand the history of the field or what’s going on.

You have written a new book synthesizing the current state of understanding on the topic of intelligence. Why did you write this book? What audiences do you hope it will reach?

I wanted to write a book that would cover the field and provide an introduction to the actual research that goes on in intelligence, the techniques used, and something that would be more sophisticated and more detailed than the books that have been done in the past. And I tried to cover the whole field. Hopefully it would be suitable for an advanced undergraduate or beginning graduate student course.

What did you learn from your students when teaching a course on intelligence who are learning about the field for the first time?

Well they’re sort of surprised and startled that a lot of what they’ve learned is wrong. And I think I’ve been able to demonstrate to their satisfaction that it was wrong. These are fairly sophisticated students that I’ve been teaching. It comes as a sort of awakening to them that there’s this whole field that they knew nothing about. It’s important to teach people in general about intelligence, regardless of the field that they go into. For example, I don’t think many physicians have ever really considered the fact that there are people who aren’t as smart as they are. So when they tell their patients something, it may not get done. I have a friend who I play poker with who is a physician who quit because he couldn’t stand the patients.  He’d tell them how to treat their condition and they wouldn’t do it. And so sometimes people don’t understand what it takes to communicate something to people of a different level of intellectual ability than their own, what they need to do and how they need to do it. How the instructions need to be concrete and directed. It’s a lack of understanding that there are people that are different than you. If you don’t appreciate that fact, it can look like other people are just being obstinate, difficult, or not doing what they should do. I particularly think college level people need to understand they are going to be coming across people with differences in cognitive ability.

4. Personal

How did you get interested in studying intelligence?

Well, in the Navy. I went to college [Boston University] when I got out of the Navy. I actually started out as an English major because I was reading a lot and enjoyed that. But I took a psychology course and right away sort of got interested in psychology. And I happened to take a graduate testing and psychometrics course and discovered [Jean] Piaget. I also learned about intellectual disability. I had a job where I worked for a company that was surveying each state to create a plan to address intellectual disability. This was during the Kennedy administration and they put quite a lot of attention on this topic. And then I decided to go to graduate school and looked around for programs on intelligence and intellectual disability, and the only programs around then were on intellectual disability. And the only book I could find that discussed intelligence besides Piaget was a book by Norman Ellis on cognition and mental retardation. And I read his book and found it fascinating and wrote him a letter saying I was interested in going to graduate school and he wrote me a letter back telling me just what I needed to do. You need to take this test, and submit this application, and so on. I did that, was accepted, and went to graduate school at the University of Alabama, took my first job at the University of Dayton, took a postdoc at Northwestern University and then ended up at Case Western Reserve University. I trace my interest in intelligence back to the Navy.  It was interesting to see the extent of differences among people. I studied intellectual disability because there were no programs on intelligence, and I think if you look around today you won’t find any programs on intelligence. Where you went to school [Peabody College of Vanderbilt University] was a place that actually specialized in intellectual disability.

You wrote a chapter “Detterman’s Laws of Individual Differences Research.”   Why did you write this chapter and which law do you feel is the most important?

I wanted to take a humorous approach to the constant criticism that much of intelligence research gets. Some of the things were my pet peeves that people criticized when they didn’t really need to. For example correlation does not imply causation. Well actually, nothing implies causation. There’s no such thing as being able to prove causation, even with experimental methods you can’t prove causation. But causation is a logical inference. So most people would agree there’s a relationship between smoking and lung cancer, even though that’s entirely correlational evidence, nobody knows exactly how this happens. We’re willing to make the inference that there’s a causal link there. So that’s just one example. I’m not sure why I wrote this chapter but people seem to like it.

What advice do you have for students who are interested in pursuing research in the field of intelligence?

To do it first of all. It’s a great field. There’s immense potential in this field. Unfortunately you have a lot more to learn than I had to learn. But it’s well worth learning and I think it’s going to yield really important results over the next twenty years. I hope I live to see some of them. It’s going to be incredible what we find out. But we’re poised on the edge of huge findings on all kinds of things. We already know a great amount and the last twenty years have been extremely productive, and I think people are beginning to realize it now in other parts of science, not just psychology but neuroscience, genetics, and so forth. If they want to study it, my suggestion is to find the person who is doing the research you’re interested in and send them an email. That’s the best advice I can give right now. I wish there was a program. Hopefully there may be some day, but right now there isn’t. There are people doing great research all around the world.

© 2014 by Jonathan Wai

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Note: This article originally appeared on Psychology Today.

Tags: causation vs. correlation, cognitive science, deliberate practice, douglas detterman, genetics, inteligence, intelligence, intelligence research, jonathan wai, neuroscience, testing

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