Intelligence, genetics and environment

Intelligence is one of the greatly debated concepts in science today. Well, maybe not so much in actual science per se, but definitely so in the blogosphere. A crowd that goes by the name of HBD (human biodiversity) advocates ideas that closely resemble those in Charles Murray’s 1994 book The Bell Curve, which (re)sparked interest in this topic, even in popular circles.

The HBD group tends to believe that genetics play most of the role in intelligence and that groups like African Americans are naturally less intelligent than Whites, while groups like East Asians and Jews are more intelligent. Therefore, any attempt to close the Black-White (income/education) gap is futile. On the other side are people who think environment is exclusively responsible for intelligence. These include left-leaning academic circles (mostly from the humanities), and this view apparently is the leading one in Scandnavia (no surprise).

I decided to look into this matter for real and see where science actually stands. Not surprisingly, it turns out that the truth is in the middle. But there is more to this.

After Murray published The Bell Curve in 1994, Neisser et al. (1996) wrote a paper summarizing all the scientific evidence at the time on intelligence. Sixteen years later, Nisbett et al. (2012) published a paper, which is pretty much an update to Neisser et al. (1996). It summarizes the current stance of science on intelligence. I ran into this paper and read it to see what actual evidence we have, because both of the extremes appear to be somewhat politically motivated. So I wanted to know where rigorous scientific analysis gets us. I’m no psychologist but the paper seemed completely impartial to me. There appeared to be no bias towards either explanation.

If I had to briefly summarize the effect of genetics vs. environment based on my reading of this paper, it would look like this: think of a good environment as a basic need for intelligence to prosper like food for the mind (don’t mind my weak metaphors). It is food in the sense that it is very basic and if you’re deprived of it, you pretty much starve to death no matter what. In other words, without a sufficiently good environment, it doesn’t matter if you’re genetically gifted, you probably will not have the opportunity to develop that gift into its full potential.

Consider the following two graphs:

intelligenceEnvironment x IQ and Genetics x IQ refer to the ameliorating effect environment and genetics have on intelligence, respectively. Start with the first panel. As the quality of the environment gets better, environment has more and more of a positive effect on IQ. The red line is like a treshold. You can think of this as the critical environment. Also note that the graph is convex (IRS) before the treshold and concave (DRS) afterwards, meaning that before the treshold if your environment improves by “one unit”, then your intelligence will improve by more than “one unit”, whereas after the treshold “one unit” improvement in environment will give you a diminishing benefit, i.e. less than “one unit” of additional intelligence.

If you want an example, think of an undernourished child. If you give him x additional calories, his intelligence will improve in the long run relative to what it would have been. Now, think of a normal person. If you give her x additional calories, her intelligence will probably not be effected in any way. Here, food is a proxy for environment and the undernourished child is left of the treshold while the healthy person is right of it.

Now consider the second panel of the graph. The evidence shown in Nisbett et al. (2012) indicates to me that genetics cannot contribute to your intelligence until the quality of your environment is beyond that critical treshold. Until then, the environment is just so bad that your genes’ effect cannot kick in. Therefore, the effect of genetics is pretty much constant and low (but not completely nonexistent) below the treshold. Once you pass the treshold, your genes will influence you more and more.

This is, however, just my way of depicting the plethora of evidence put forward in the paper. The general picture that experiments show is that in households with a low socioeconomic status (SES) environment explains most of intelligence, while in high SES households genetics does.

What one must understand is that intelligence can be trained. There is a lot of research on this, one I particularly like is about summer vacations. Students “lose IQ” over the summer. So here is this construct called IQ, which according to some people is purely genetically determined. Then how on earth could any healthy young person lose it as we progress through time? There is a lot of other proof that intelligence can be trained.

If you don’t believe this ask yourself why an IQ test would be different from any other standardized test. Any standardized test can be learned to a certain extent. Think of the GRE or the SAT: if you just do practice tests regularly, you’ll get better at it. Your initial 155-160 quant score will crawl up to 165-170. The same also holds for IQ tests of course. That is how you can gain and lose intelligence. In general, if you’re being intellectually challenged on the daily, you will be more likely to do well on such a test than if all you do is flip burgers, watch TV and get drunk with friends.

Of course intelligence is not explicitly trained per se. As the burger flipping example shows, it is more that your everyday activities can be such that they train your intelligence even if you don’t intend for your intelligence to be trained. Hence the importance of environment. This also explains why genetics can’t help until your environment is stimulating enough.

Going back to the summer vacation example: do you think all children lose the same amount of IQ over the summer? Of course not. Research shows that low SES children lose more, while high SES children may even gain IQ. All these lost summers can account for a lot of the low-high SES academic gap (and there is a large gap).

Obviously, once we compare children whose environments are similar, genetics come into play. This is why genetics is a better predictor of intelligence in high SES households.

So what about the usual questions? The Black-White gap? Asians and Jews? I will look at these briefly.

First, African-Americans with a significant European heritage do not have higher IQs than their “less European” peers. The same applies when mixed race children are compared to “purely” Black children. Matter of fact when Black children are adopted by Black and White families (both middle-class), those raised by White families have an IQ 13 points higher than those raised by Black families. Wow, this is almost the whole Black-White gap. It appears thus Black people are largely kept down by their environment, not by genetics. Their situation can be significantly ameliorated.

For Asians, most researchers cite cultural differences (exhibit 1, 2, 3). For Jews as well, the main view is that there are no sharp genetic differences, it’s mostly culture and environment. It must be noted that even if we take the Jewish average IQ to be 115 (which is the highest estimate), the high number of Jewish Ivy League professors and Nobel laureates would still not be accounted for. So there must be a significant environmental factor there.

Finally, let me talk about a third factor, which can be thought of as a mix of genes and environment: character traits. Although traits such as self-regulation and self-discipline have been linked to higher intelligence, research has been rather scarce. I would argue that it makes a huge difference whether or not you’re able to sit down and study, plan ahead and keep your plans, decide to postpone fun activities if necessary, persevere and not immediately give up and so on. These are traits that can be learned to a certain extent, albeit it’s not as easy as learning a regular skill. It may also be important whether your parents encouraged you to develop these skills as a child or not.

One may also think of personality (i.e. traits which cannot be changed). One thing I can think of is that introverts may be more successful in developing the abilities mentioned above. So in this case, personality can help. Also consider the graph above once more. It could be possible that personality can help the red treshold shift to the left or right (and with it, the graphs will shift too); meaning that if your personality type is advantegous for developing intelligence, then you will be able to flourish in a worse environment than the regular person, and vice versa.

So to summarize:

  1. Environment is an important predictor of intelligence in low SES households, therefore there is certainly a lot of room for improvement there. We should not write low SES children off, we should help them and provide them with a better environment if possible. Interventions do work.
  2. Genetics play a role but if only genetics influenced intelligence, the IQ gaps would probably be much smaller. Consequently, we cannot dismiss whole groups of people as having genetically inferior intelligence.
  3. Other (learnable and non-learnable) traits also contribute. There should probably be more emphasis on instilling such traits (like self-regulation) in children, especially in low SES households.

There is a lot more to this topic, but these are the general points. If you want to read some more quick facts I urge you to read the abstract of Nisbett et al. (2012). If you want more detail and want to hear about all the experiments mentioned and not mentioned here, I suggest you read the whole paper. If you wish to dig even deeper, the paper has 8 pages of references, so check that out and down the rabbit hole you go. You might even strengthen your intelligence in the process. After all, what’s more intellectually stimulating than reading academic papers?


2 thoughts on “Intelligence, genetics and environment

  1. Pingback: ZeeConomics | The consequences of school choice

  2. Pingback: ZeeConomics | Political beliefs and intelligence

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