Intelligence quotient — or IQ — can be an awkward topic.

As I wrote yesterday, there's a mountain of research showing that it's a genuinely powerful predictor of your health, prosperity, and well-being. But because IQ is partially hereditary, and resistant to change, it conflicts with a lot of modern values about self-determination.

Today there's an endless supply of psychological books and TED talks that are dismissive of IQ, or argue that it can be supplanted.

The latest installment is Grit: The Power of Passion and Perseverance. Its author, University of Pennsylvania psychologist and MacArthur "genius" Angela Duckworth, has said her measure, "grit" — i.e., strength of character — "beats the pants off IQ." (That's dubious. Slate has a great piece explaining why.)

And if it's not grit, pop psychology has a multitude of other buzzwords for qualities we can cultivate to take control of our destinies: presence, willpower, perseverance, you name it.

"It might be the case it would be worse if people’s IQ was totally malleable"

These personality factors do have some importance. But none are as well-studied, or as reliably predictive, as IQ. Personality traits, a recent study found, can explain about 6 percent of the variance in test scores for students under age 16. IQ can explain around 25 percent, or an even higher proportion, depending on the study. "You get these small studies on whatever it is — grit — and it’s nothing like as extensive a research background that intelligence has," Stuart Ritchie, an intelligence researcher at the University of Edinburgh, tells me.

Make no mistake: People have done very dumb things with IQ in the past, like the eugenics movement and arbitrary intelligence cutoffs for the death penalty. But those controversial topics are about the application of IQ, not the theory. I wanted to learn about the theory. So I called Ritchie.

Our conversations (over phone and email) have been edited for length and clarity. My questions have been edited to make me sound slightly smarter.

Brian Resnick: One of key findings in intelligence research is that people who are good at one mental task tend to be good at them all. [Psychologists call this overlap the "G" — or general intelligence — factor.]

This is what blows my mind: Your score on a task that measures how fast you can turn off a blinking light (one of many intelligence tests) is correlated with your scores on verbal and spatial reasoning.

This goes against the popular idea that there's an inherent trade-off in intelligence. That we can't be great at everything.

Stuart Ritchie: I’m looking at a table right now of some data from our sample here in Edinburgh with reaction time and some measures of verbal ability. They correlate with each other. It’s a totally routine thing that we see.

We’ve been using this really cool effect in our sample called inspection time. A little shape gets flashed up on a computer screen, and either it has a long line on the right-hand side or a long line on the left-hand side. It’s like an n-shape.

It flashes up on the screen for a very very brief period of time. At 0.6 milliseconds, performance [stating which side has the longer line] is totally random. Nobody gets it right. It’s onscreen for too short of time.

If you put it up for 500 milliseconds, then everyone gets it right, because it is super obvious.

People differ in the duration in which they can reliably distinguish [which side is longer]. And that, called their inspection time, correlates with vocabulary performance, correlates with all these other IQ tests.

BR: I found a lot of this research to be depressing. In your book, you lay out a compelling case that IQ reliably is correlated with longevity, economic success, and physical well-being. You also make it clear that IQ doesn't change all that much throughout our lives. We're kind of stuck with what we've got. I guess I find it unfair.

SR: First of all, the most important thing to say is that it doesn’t matter if it’s depressing if that’s what the research says. One can’t deny it.

Think about how it would it be if it was the other way around; there might actually be some bad outcomes.

Because then parents would be able to totally control their kids with bad parenting, and wreck kids’ IQs for the rest of their lives. Governments could have big influences on people’s IQs by enacting different policies toward different sets of people in the country.

On the other hand, it is the case that most of the attempts we have to really boost IQ — with things like brain training games, and so on — have been pretty disappointing. But it doesn’t necessarily mean in the future we won’t work out more target direct ways to improve IQ.

[Note: In the developing world, increasing nutrition — namely through iodine supplements — has done a lot to increase IQ scores. And overall, IQ across the globe is rising. These are good trends, and lend evidence to the idea that bettering a child's environment makes the child smarter.]

BR: Do differences in IQ make a difference between individuals? Or are these differences just pronounced when looking at large groups of people? Basically, if I have an average IQ of 100, to what extent should I be jealous of someone with an IQ of 110?

SR: It's very difficult to answer. There’s a whole constellation of other traits that you might have — that are not correlated or only weakly correlated with intelligence — that are also going to have an influence on your success in life. So on an individual level, it’s hard to predict.

But on average, for people who have an IQ of 100, it’s unlikely they are going to be producing major creative accomplishments, setting up the next Facebook or Twitter. If you look at people who have been extremely successful in creative professions — I don’t know the precise number, but there is going to be a cap, and it’s extremely unlikely if you’re below that cap that you’re going to be able to perform at a high creative level.

BR: Really? Average people can't do incredible things?

SR: It’s just that you simply don’t see people who have. Or very rarely you see people who have average intelligence in samples of high creative output people.

We should get on the record that heritability does not mean immutability. I think you’re probably stuck within a range of what you have. We’re not going to turn someone with an average intelligence into a genius anytime.

And it must be said there are other things that can compensate.

BR: Thank goodness. Like what?

SR: Conscientiousness, for instance — or maybe you want to call it grit — can probably compensate to some degree for having a slightly lower intelligence.

BR: In the book you dismiss the idea of emotional intelligence — the idea that people can be adept at empathizing, and that this can matter more in jobs that require a lot of social interaction than pure IQ. What's your case against emotional intelligence?

SR: People ask this all the time. The answer is that, sure, emotional intelligence correlates with some measures of life success. But to a large extent, this is just because emotional intelligence is a re-description of a combination of IQ and personality — that is, a re-description of psychological traits that we already knew about. It [also] does correlate with "G" [meaning people with high IQs are also high in emotional intelligence].

In general, I’m not sure how useful it is just to relabel stuff we already know. And in any case, in most models where they compete to explain variance in, say, job performance, IQ does a much better job.

BR: Are there any pitfalls to having a high IQ? I know from research in political science that some of the most engaged, informed people are also some of the most susceptible to motivated reasoning (i.e., they're more likely to be dismissive of information that runs contrary to their worldview).

These studies in political science don't focus on intelligence. But maybe there's something here that applies to intelligence: If you're very smart, isn't it easier to reason the world into a shape you prefer? Just think about the cadre of American columnists (we might assume they're smart people) who wrote smart, convincing, but wildly wrong columns about Donald Trump's chances in this election.

SR: We might notice in our daily lives that our fellow scientists and journalists are prone to motivated reasoning and that they sometimes make (in hindsight) ridiculous mistakes, like forecasting that Trump will be beaten easily by Jeb Bush. But this is, sadly, nothing compared to the levels of motivated reasoning and reasoning errors that you’d see from a sample of people lower in the distribution of IQ.

If you put people with lower IQs into the positions of journalists, political commentators, etc., I suspect they’d simply make even more mistakes.

BR: Are people with higher IQs any happier for it? It would make sense: They tend to be wealthier, healthier, and more successful.

SR: The correlation between IQ and happiness is usually positive, but also usually smaller than one might expect (and sometimes not statistically significant). This paper, for instance, finds a positive correlation, and finds that it’s likely due to the reasons you mention there, such as health.

BR: So is there nothing high IQ people are worse off for? Give me something.

SR: Shortsightedness! [As in, having to wear glasses.] That’s the one thing that’s consistently been linked to having a higher IQ. I can’t think of anything else that’s as well-replicated as that.

BR: I want to talk a bit about why people are turned off by the idea of IQ.

There’s a lot of research that finds we so very quickly like to see the world in terms of "us versus them" that we tend to do pretty horrible things to the "them."

SR: Yes, those are the things that replicate in social psychology.

BR: The "sorting" of people into groups is what makes me uncomfortable. Humans have a remarkable ability to marginalize people we see as "less than." IQ might be the measure of smarts, but we sure can do dumb things with it.

SR: A lot of the reason people in the UK are upset about the idea of intelligence tests is that for many, many years we had a selective school system that actually did exactly what you are saying. You pass the IQ test at age 11, the 11-plus as it was called, and you get put into either a grammar school — where you had passed the test and you go on and do complicated subjects, complex things, classics — or you get put into the secondary modern school, where it’s broken down, the teachers aren’t as good, the school isn’t well-maintained, behavior is not so good.

So a lot of people feel resentment. Those who were on just the other side of the passing mark went on to go to a really nice school. So this kind of division is one reason why people don’t like intelligence testing.

BR: Maybe this is the source of the tension. We want to hold on to the idea that we can better ourselves. (And, as you point out, we can. Increased years of school, at least, seem to be important to raise our IQs). But here's the tricky part: We can use these tests to make predictions of who will be the best student, worker, etc. These are at odds. We want to hold on to the idea that people can get better while making predictions that seem to limit that potential. Does that make sense?

SR: No one is saying these issues are easy at all. The only way we’re going to get proper debates and proper ethics of how we deal with these things is if people accept the scientific evidence on these topics. At the moment, you don’t get the debate.

What's the best optimal societal way to use these tests? I don’t know. But if we don’t all agree that the prediction is there in the first place, we’re in big trouble.

History in general has progressed to marginalizing fewer people. Gay rights and women’s rights, and even more recently animal rights. There is societal progress away from societal-level marginalization of people. But, yeah, I totally understand your concern.

BR: Is there any reason why a person would want to know their IQ?

SR: I don't think it's particularly useful.

I don't know what my IQ is. One of the guys in the psychology department here knows, because he tested me. And there's always a slight awkwardness when we're talking about IQ. He knows what my IQ is. But I have not, and I have no interest in knowing. Maybe for the reasons you mentioned earlier. I know how important it is, and I'd be depressed if I found if it was low.

Proof of evolution you can find on your own body