Jonah Lehrer has a post summarizing recent findings on the distribution of intelligence gains across the population. The really provocative finding, from a team led by Jonathan Wai at Duke, is that there have been gains in fluid intelligence across the distribution, not just those at the left end of the bell curve, i.e., the low-hanging fruit hypothesis doesn’t quite fit the facts. So it seems that there is some kind of society-wide environmental stimulation at work. Lehrer writes:
It obviously has to be extremely widespread, since the IQ gains exist at the population level. One frequently cited factor is the increasing complexity of entertainment, which might enhance abstract problem solving skills. (As Flynn himself noted, “The very fact that children are better and better at IQ test problems logically entails that they have learned at least that kind of problem-solving skill better, and it must have been learned somewhere.”) This suggests that, because people are now forced to make sense ofLost or the Harry Potter series or World of Warcraft, they’re also better able to handle hard logic puzzles. (The effect is probably indirect, with the difficult forms of culture enhancing working memory and the allocation of attention.) As Steven Johnson argued, everything bad is good for us, especially when the bad stuff has lots of minor characters and subplots. HBO is a cognitive workout.
That said, environmental stimulation remains an incomplete explanation. Even for those on the right side of the curve, intelligence gains probably have many distinct causes, from the complexity of The Wire to the social multiplier effect, which is the tendency of smart people to hang out with other smart people. (In this sense, gifted programs in schools might help drive IQ gains among the right tail.) The question, of course, is whether such factors have really changed over time. Has it gotten easier for smart people to interact with each other? Are those on the right side of the IQ distribution now more likely to have children together? These questions have no easy answers, but at least we now know that they need to be answered. [Emphasis added]
I imagine that the answer to both of Lehrer’s questions is yes, but of course it is very hard to know for sure.
One additional note on the low-hanging fruit hypothesis from Lehrer’s post:
What makes this mystery particularly noteworthy is that many of the explanations for the Flynn effect seem particularly relevant to the left side of the bell curve, or those with below average scores. This suggests that most of the intelligence gains have come from solving low-hanging fruit, fixing those glaring societal inequalities that meant millions of children lacked access to adequate food, education and medical care. Since we’ve made progress on these problems, one might suppose that the Flynn effect would start to fade, at least in developed nations. (All the low hanging fruit is gone.) Sure enough, some studies have concluded that the Flynn effect has begun to disappear in Denmark, Norway and Britain. [Emphasis added]
If we buy the Garett Jones hypothesis regarding national IQ and national productivity, and I do, the apparent existence of a near-term upper bound is interesting. To refresh your memory, here is Jones’s abstract:
A recent line of research demonstrates that cognitive skills—intelligence quotient scores, math skills, and the like—have only a modest influence on individual wages, but are strongly correlated with national outcomes. Is this largely due to human capital spillovers? This paper argues that the answer is yes. It presents four different channels through which intelligence may matter more for nations than for individuals: (i) intelligence is associated with patience and hence higher savings rates; (ii) intelligence causes cooperation; (iii) higher group intelligence opens the door to using fragile, high-value production technologies; and (iv) intelligence is associated with supporting market-oriented policies. Abundant evidence from across ADB member countries demonstrates that environmental improvements can raise cognitive skills is reviewed.
Jones places heavy emphasis on the low-hanging fruit hypothesis in the paper, favoring interventions designed to improve infant brain health. One wonders about the strategies we might pursue to drive intelligence gains at the right end of the bell curve.