The scholar and the world! The endless strife,
The discord in the harmonies of life!
The love of learning, the sequestered nooks,
And all the sweet serenity of books;
The market-place, the eager love of gain,
Whose aim is vanity, and whose end is pain!
Longfellow, Morituri Salutamus

Why are some people healthier than others? This might sound like a bit of silly question. The answer is surely obvious: some people eat better and exercise more than others. But is that all there is to it? Couldn’t ‘healthiness’ be attributed, at least in part, to our genes? Might some of us be born with a greater capacity for health than others? We know that various physical traits – eye and hair colour, height, weight, certain specific genetic disorders – absolutely are inherited, so why not a general factor of healthiness?
For the sake of argument, let’s agree that we all possess a measurable health quotient (HQ) and that we’re all born with a different predisposition for healthiness. We know that this genetic component cannot account for the entirety of our HQ as it’s an observable fact that eating burgers and doing press ups both have an impact on our health.
I’m pretty sure you can see where I’m going with this. Twin and adoption studies have consistently pointed to the idea that our intelligence (and pretty much every other trait that’s been investigated) is somewhat due to our nature (genes) and partly accounted for by how we are nurtured (environment). Estimates vary but it’s generally agreed that the portion IQ variance which is accounted for by genes rises from about 45-50% in childhood to around 75-80% in adulthood. And the proportion that’s due to our shared environment (parenting) starts at about 30% and washes out almost entirely by adulthood. At the same time, other environmental effects become increasingly important with education and peer groups taking over the role of parents. Why might all this be?
If we return to our health analogy, we can see that as children how healthy we are depends in large part on the environment our parents create for us. If they force us to eat our greens, get plenty of sleep and refuse to let us sit around playing computer games all day every day then we will be healthier as a result of their interventions. When we grow up and leave home, our parents are no longer the boss of us and we can do whatever we want. We decide whether we want to go to the gym or stuff our face with cream cakes. How we decide will be partly due to our genetically influenced predisposition for healthiness, and partly it will be due to factors such as trying to impress friends or potential mates. We mostly stop caring about what our parents might think if we don’t eat up our broccoli.
If you decide you want to run a marathon, you’ll commit to eating more healthily and sticking to a training regimen. For the duration of your training the environmental impact on your HQ dramatically increases. After you’ve successfully completed your marathon you might decide to stop training and then the environment you experience makes you less healthy. However, you might decide that you love training and pick up a lifelong habit for healthy living. Of course, training will never entirely overcoming your genetic propensity for health; no matter how hard you train you’ll never be able to beat some people.
Our intelligence follows a similar path. As children our parents can positively affect our environment by reading to us, giving us a positive attitude towards school and helping with our homework. All of this equates to a shared environmental contribution to intelligence. But, as children become teenagers, parents have a less and less effect until their adult children finally fly the nest entirely. The environmental role of parents is overtaken by that of peers, choice of leisure time activities, jobs etc. If we decide to become the cognitive equivalent of a couch potato, we will lose some of our intelligence. If we decide to ‘exercise’ by reading improving books, having a peer group who are interested in the world and prepared to challenge us, and choose a cognitively demanding career, then we should see a boost to our intelligence.
How long will this boost affect our intelligence? Well, how long does physical exercise and good nutrition affect our health? Eventually, our environment will catch up with us. But, just as some people develop an intrinsic love of healthiness, so do others settle on an approach to life that has a self-sustaining affect on their intelligence. Very few environmental affects will by anything like permanent (a serious head injury is an example of a possible permanent environmental effect) so we have to keep working at being cleverer if that’s what we want to be.
We also need to be aware of how our genes co-opt our environment. If you’re very tall and quick and live in a society that values basketball, then your environment is likely to change in order to give you more practice at playing basketball which will then have a direct impact on your HQ. Eventually, most young basketball players, no matter how talented, will stop playing basketball and, unless they’ve internalised a habit of healthiness, they will likely see their HQ decrease.
Likewise, children with the advantage of a genetic endowment that helps them perform well academically will tend to seek out and be given opportunities where they can shine ever more brightly. They’re likely to value academic success more and thus work harder. They’re more likely to experience a cognitive boost by staying in education for longer. Eventually, most people will leave academia and their environment will shift. One way in which the effects of the environment may have a more or less permanent effect on intelligence is in the choices that open up for us. Better academic qualifications correlate well with more cognitively demanding jobs and therefore increase the likelihood that will we have brighter colleagues. Hence, what might have begun as a fairly small genetic advantage is multiplied by positive environmental factors and becomes a significant advantage.
All of this is to say that it seems plausible that our intelligence is, in some ways (obviously not in all) similar to our physical health. Just as we have to keep working to maintain our health, the same appears to be true for our intelligence. There’s no doubt that attending school for longer results in clear IQ gains in adulthood, but unless children acquire a habit for intellectual curiosity and challenging themselves, these gains may eventually dissipate.
Just as we’re not really sure how to create a society in which everyone develops an intrinsic desire to be healthy, there’s no certainty about how to support students to acquire an internalised love of learning*. One way to achieve this might be to adopt these principles in schools so that they become habitual for teachers and students:

  1. Open children’s intellectual vistas by exposing them to the most powerful and culturally rich knowledge available, and then encouraging them to critique this information to arrive at new ways of thinking. Never devalue knowing things and always encourage thoughtful questions.
  2. Encourage children to stay in academic education for as long as possible by exciting their curiosity and providing an environment where intellectual pursuits are supported and rewarded. The longer children stay in education the wider the choice of possible careers they will have access to.
  3. Make what efforts we can to shape the peer culture in schools so that children come to believe it’s cool to be cleverer and that hard work is its own reward. Although most of these relationships might not survive into adulthood, everyone can acquire more of a taste for thinking more about the world and therefore be more disposed to others who think similarly.

Whether or not this results in a measurable increase in IQ is, I think, irrelevant. I think we can all agree that intellectual curiosity and a life long love of learning are things we want for all children. This seems like a good bet for getting what we want.
* When I say “love of learning” it’s important to distinguish between biologically primary and secondary modules. A love of biologically primary learning is probably a species-wide adaptation  and probably does little to improve abstract reasoning. A love of secondary learning is dependent on cultural innovation and does not come to us naturally.