Small Gray Matters

Jonah Lehrer has a post over at Frontal Cortex today that follows up on his article in Seed a couple of weeks ago arguing that exceptional abilities are the result of extensive practice rather than genetic predisposition. My own view is that they’re probably not; or at least, I’m not sure the question is a coherent one to begin with. At any rate, here’s what Lehrer says:

For one thing, there’s a lot of empirical evidence that suggests I’m right. Virtually every psychological study that investigates expert “performers” - from chess grandmasters to concert pianists to brain surgeons - concludes that what separates these individuals from their peers is the amount of “deliberate practice” they are willing to endure. If there is an innate difference between Yo Yo Ma and a mediocre cellist, or between Tiger Woods and your golfing uncle, it is a willingness to practice, and not an innate aptitude for the cello or the 9 iron. As K. Anders Ericsson, a cognitive psychologist at Florida State University, wrote in his influential article “The Role of Deliberate Practice in the Acquisition of Expert Performance,” “The differences between expert performers and normal adults are not immutable, that is, due to genetically prescribed talent. Instead, these differences reflect a life-long period of deliberate effort to improve performance.”

I incline to disagree with this for several reasons. First, I think it mischaracterizes the notion of heredity. Saying that variance in a behavior is under genetic influence is patently not the same thing as saying it’s immutable. Consider that, in Western societies (where malnutrition isn’t an issue), height is almost entirely under genetic control. Does this mean height is immutable? Of course not. Take a child born to 6’6” parents and deprive it of its basic nutritional needs, and it’ll be lucky to reach average height. Saying that someone has ‘tall genes’ isn’t saying they have a fixed endowment that’ll express itself in the same way regardless of environment. It’s saying that, across a range of environments, a person born to tall parents is more likely to be tall than other people around them exposed to the same basic environment. It’s not clear why this should be at all controversial. Does anyone really believe that if 10 people sampled at random were each forced to practice the piano for exactly 10,000 hours, they’d all attain exactly the same level of skill?

A second problem relates to the false dichotomy between the effects of practice and genetically prescribed talent. These aren’t opposing factors; in fact, they’re completely orthogonal to one another. Saying that someone practices a lot isn’t actually saying anything about whether the contribution to the behavior is under genetic or environmental influence. The reason for this is simple: any number of genetic factors could drive a person to practice an ability to a greater or lesser degree. These include everything from very general factors such as fluid intelligence to specific cognitive abilities to personality factors to creativity to aesthetic sensibilities.

Take the case of prodigious musical ability. It may be comforting to think that we could all be Yo Yo Ma if we really wanted to. But it’s almost certainly not true: the vast majority of the population would never be able to play the cello like Yo Yo Ma no matter how much they practiced or how early they started. And the reason isn’t that there’s something magical about Yo Yo Ma’s brain—some single amorphous genetic talent he possesses that other people just don’t. It’s much more likely that he simply possesses lots of little genetic quirks that virtually no one else happens to have the right combination of (for playing the cello really well, at least).

What does it take to be Yo Yo Ma? Well here’s a very short list of just a few factors that are likely to be under considerable genetic control and undoubtedly make one more likely to be a good cello player: a certain amount of general intelligence; a certain amount of visuospatial ability; good sequencing skills; a liking of music; absolute pitch; long, slender fingers; agility; a tremendous degree of personal motivation; and high levels of conscientiousness. Of course, plenty of people (indeed, the vast majority) will be above average on one or more of these dimensions. But that’s not the point. The point is that being a great cellist isn’t about having a magically different brain. It’s about having a particular combination of abilities, many of which are genetically influenced, that just happens to make one well-suited to playing the cello. That’s not in any way denying that practicing thousands of hours is necessary in order to achieve Yo Yo Ma’s stature. It’s just saying that it’s not sufficient.

Lehrer actually seems to concede this point to some degree when it comes to personality factors:

If there is a genetic element linking Mozart and Jordan it is the talent for practice itself, a willingness to endure the endless hours of sweat and toil required of all great performers.

This is quite clearly true, since about half of the variance in personality traits like conscientiousness is sucked up by additive genetic influences in most twin studies. But there’s no reason to suppose the buck stops with personality. Why should Mozart and Jordan’s relevant genetic endowment differ from other people only when it comes to motivation? Isn’t Jordan’s height under genetic influence? Should we really believe that a 5’3” male with a 12” vertical leap could become the world’s greatest basketball player given enough effort? Or that someone who’s tone deaf and has a congenital hand tremor is as likely to produce virtuoso violin performances after 10,000 hours of practice as someone who has absolute pitch and excellent motor control? These are extreme examples, but they’re only quantitatively and not qualitatively different from the vast majority of individuals, who are likely to be somewhat taller than 5’3” and to be neither tone deaf nor have absolute pitch.

A third problem with the claim that expertise doesn’t depend on innate factors stems from the fact that none of the evidence Lehrer cites, including Ericsson’s line of research, really addresses the fundamental issue. Ericsson’s work, particularly the Psych Review article Lehrer cites, is a textbook case of attacking a straw man (just to be clear, I think it’s excellent research when framed as a study of expertise or of the structure of memory; it’s specifically the claim that expertise isn’t innate thats problematic). The argument has the following form: (a) in virtually all expert populations studied to date, long hours of practice are a defining feature; (b) the number of hours of practice is positively correlated with ability; (c) most people don’t practice a lot and aren’t very good; therefore we can conclude (d) that practice is responsible for expertise and innate factors have little or nothing to do with it.

What’s the problem with this reasoning? Well, consider the following analogue often found in the developmental psychology literature: (a) violent parents tend to abuse their children; (b) those children tend to perpetuate the ‘cycle of violence’ by abusing their own children when they grow up; (c) the amount of violent behavior displayed by children correlates with that displayed by their parents; so (d) we can conclude that parental behavior causes aggression in children.

The problem with the latter chain of reasoning should be obvious: one can’t conclude that parental environmental factors are the key contributors to children’s behaviors without explicitly modeling the shared genetic variance, because correlation doesn’t entail causation. And when you do model the genetic variance, parental influence almost invariably represents a negligible amount of the total variance, whereas additive genetic factors typically account for about half. This may be counterintuitive, but the explanation is simple enough: violent parents pass on violent genes to their kids, and the genetic contribution seems to dwarf the influence of parents’ overt behavior.

The exact same problem applies to correlational studies of expertise. It’s surely not remarkable to note that thousands of hours of practice are necessary to become a world-class expert in almost any field. The very notion of ‘expertise’ practically requires as much: if it could be acquired in a matter of hours, everyone would be an expert, and the term would lose all meaning. The issue isn’t whether or not practice is the proximal cause of expertise. It’s whether or not genetic factors underlie the drive and desire to practice itself. And that’s a question that simply cannot be addressed without explicitly modeling the genetic contribution to a behavior. You simply can’t tell just by studying an individual grandmaster who’s played 60,000 hours of chess whether they’re that good at chess because they’re naturally gifted, or because they were pushed to play chess in spite of a lack of natural ability.

Consider: if you had an IQ of 80 and had trouble learning the rules of chess, would you keep playing the game and making mistakes? Probably not. If you were merely mediocre, and lost to everyone else in your chess club, would you keep plugging away at it for thousands of hours? Possibly, but it’s unlikely. The people who end up practicing a single skill for thousands of hours are almost invariably those who (a) love what they do; (b) have an unusual level of drive; and (c) find it comes naturally to them. People tend not to practice at things they don’t like, can’t keep at, or don’t seem to be any good at. All of these dispositions are, of course, at least partially (and probably substantially) under genetic control.

But there is virtually no evidence that expert performers are born with extraordinary brains. In fact, the average IQ of people at the top of their field - whether they are surgeons or politicians, pianists or painters - equals that of the average college student. In other words, their expertise is very specific, confined to a particular “cognitive domain”.

Two problems here. First, as noted above, expert performers don’t have to differ in some general intellectual domain in order for their skills to be driven by genetic influences. Why shouldn’t we think that oratorical, artistic, or motoric skills are under some amount of genetic control independently of general factors such as fluid intelligence? To argue otherwise would be to disregard any amount of evidence from behavioral genetics. And secondly, the domain specificity argument is also a red herring. The fact that skills acquired in one domain don’t easily generalize to other domains doesn’t say anything about the role of genetics if one grants that genetic predispositions can be highly specialized, or that different domains rely on different combinations of abilities.

But practice doesn’t just change which brain areas are activated by a certain task. It also leads to anatomical changes within those same brain regions. For example, the brains of expert violin players have swollen representations of the fingers of their left hand in the somatosensory cortex. This increase in neural space makes Bach easier to play.

Again, this is true, but says nothing about the role of nature and nurture. The issues has never been whether plasticity occurs as a result of practice (it does!), it’s whether variations in the degree of plasticity across individuals are due to genetic or to environmental factors. Expert violin players are presumably individuals whose somatosensory cortex is capable of adapting to the demands of an instrument over time. It’s entirely possible that the vast majority of humanity doesn’t display the same range of plasticity. Without modeling the genetic variance, there’s no way to tell.

This leads to the gauntlet Lehrer throws down in a comment following the post:

In fact, the only innate talent that talented people seem to contain is a talent for practice. But if there are scientific studies that suggest otherwise, I’d love to hear about them.

Just to reiterate, let’s be clear that none of the data Lehrer discusses in his post offer any support for the notion that innate differences don’t contribute to expert performance and skill acquisition. In the absence of direct evidence, the reasonable position would be to default to estimates of heredity obtained in non-expert domains as an appropriate estimate of the genetic variance. For example, fluid intelligence and most major personality dimensions are around 50-60% heritable in most studies. Given such results, the default hypothesis should probably be that expertise is under substantial genetic control.

That said, there’s a big problem associated with the very notion of estimating heredity for expert populations, which is that the estimate obtained will be highly dependent on the type of sample used. If, for example, you were to recruit a genuinely random sample from the population of, say, American adults, the likely result would be massive overinflation of the environmental contribution to expertise. The reason is that, for any given domain of expertise, there are only a small number of experts, and the vast majority of the population has never so much as attempted to acquire the ability in question. By way of analogy, if you studied the genetic contribution to ice hockey-playing ability in 12 year-olds living in central Arkansas, virtually all of the variance would be environmental, simply because most kids in central Arkansas have probably never laced up skates in their lives. Conduct the same study in Quebec, and a large chunk of the variance will be genetic, because hockey is heavily emphasized in the culture and almost everyone gets the opportunity to try their skills out.

The opposite extreme isn’t very useful either: if you conducted a twin study that only sampled experts with more than, say, 10,000 hours of practice in a given domain, you’d inflate the genetic variance, since there’d be a severe reduction in environmental variance in the sample. Put differently, when everyone gets the same environmental treatment, any differences in behavior must be the result of genes (or just random noise).

What’s the happy medium? Well, there really isn’t one. But probably the best indirect evidence stems from studies that have looked at genetic and environmental contributions to skill learning on a compressed timeframe (i.e., across hours instead of thousands of hours). A study of this kind was reported by Fox et al. in Nature in 1996 (“Genetic and environmental contributions to the acquisition of a motor skill”). In it the authors demonstrated convincingly that a substantial portion of the variance in both levels of performance and rates of skill acquisition was under genetic control. The latter point is particularly compelling given the current context, because it’s easy to forget that people can differ not only in how good they are at something, but in how fast they pick it up. Saying that thousands of hours of practice are required to become an expert is misleading, in that some people might need 12,000 and others only 7,000. These aren’t trivial differences.

In sum, what can we conclude about the heredity of expertise, given available data? The answer is, unfortunately, not much. Virtually all the data promoted as evidence for a practice model is irrelevant, because it attacks a straw man. The issue isn’t whether practice leads to expertise, it’s what gives rise to the tendency to practice a particular skill in the first place. Conversely, there isn’t much hard data that does approach the issue from the appropriate perspective (i.e., that of behavioral genetics). So in the interim, the appropriate position is probably to default to existing estimates obtained in non-expert domains, and maintain that it’s a bit of both: genetic and environmental contributions both influence expert performance. It’s not clear that we’re going to get a more meaningful answer.

Tuesday, August 15th, 2006 at 11:32 pm.
Filed under musings, behavioral genetics.
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