Medical experts argue whether dwarfism justifies aborting a fetus or warrants painful limb-lengthening surgeries, but advocates within the national nonprofit Little People of America argue that their lives are perfectly OK.
Posted by razib at 06:13 PM
Earlier today “Guessedworker” commented on my previous post that offered a reductionistic hypothesis for intra-racial attraction. He seemed to think that I was offering a “Blank Slate” explanation and was being “Oedipal.” In an IM chat with a friend, the same issues of relationshp to Freud came up. This really surprised me and was frustrating, since both are regular readers of GNXP, and I began to wonder how unclear I was being.
The thing is, I never think of Freudianism when I propose anything, because I conceive of it as just another religion! I don’t even notice that I might sound Freudian because I think that paradigm is pretty unscientific, so confusions of terminology don’t register in my mind. So I apologize for the navel-gazing and inability to look beyond my own horizons. My hypothesis was based on this study. I admitted that it was provisional and I was more illustrating a way to think about a problem than offering an air-tight solution to it. Physical attractiveness is such a multi-faceted topic that I approach it with trepidition, though I do broach it in a crass fashion now and then (this is mostly to entertain and lighten the atmosphere).
But back to the general issue, was I being a “Blank Slater”? I pointed to language acquisition as a rebuttal to that assertion. There is a general consensus that language is something that has a deep biological root. Even the neural connectionists agree on that (though they reduce the biological element to very atomic units that “emerge” over time into the complexity that we see [hear]). At this point, a Pinkerian-Chomskyian model seems ascendent, proposing a “Universal Grammar” and “Language Instinct.” So is what language you speak determined by your genes? No!. It is determined by your peers! It is a case where the genes set parameters and constraints, and various factors in your environment come together to “crystallize” your linguistic skills and proficiencies.
Moving even further into generalities, this sort of typology, “Nature vs. Nurture,” needs to really be discarded. If there is something you take away from the blog, that should be essential. I didn’t give the most glowing review to Matt Ridley’s new book Nature via Nurture, because I thought that the central thesis was exceedingly banal. But was it? Our society still uses the term “Nature vs. Nurture” as if the two variables are always at cross-purposes. Ideas like the extended phenotype, which have been around for 20 years have obviously not made it into the public consciousness (the idea that genes can influence your choices of environment, enriching your genetic predispositions and heightening relative genetic fitness, etc.). For a specific example, look at the study of the MAOA gene. While those with high levels of MAOA tended not to become abusers even if abused, what one must note is that even those with low levels of MAOA did not become abusive if not subjected to abuse. This is not a case of environment and genes being at odds, rather, the problem (in this case) is the intersection between gene and environment.
On this blog we tend to focus on genetics. There are many reasons that I do this, speaking for myself.
1) People tend to be less comfortable with biology than they are with psychology and sociology or anthropology, so the default explanations tend to be the latter, and this can be distorted to the most bizarre lengths (ie; the idea that gender is totally socially constructed).
2) I have a strong interest in science, I want to share that and meet like minded people.
3) New technologies and methods are making the genotype a very rich field for study and pointing toward therapy of many diseases that have been relativelly immune to talk therapy or other “environmental” redresses.
4) There are technical issues I’d like to bring to the fore. As an example, I want to make more well known the technical definition of heritability to the lay public. In sum, when we say that a trait is 50% heritable, that does not mean that everyone has a 50% genetic component in phenotype X. Rather, 50% of the variation of a trait within the population is due to genetic variation.
Let me be clear, that does mean I think that environmental factors are irrelevant. Dogmatic hereditarians (who are usually not scientifically trained in any way) try and find genes or biological causes for everything. The on-off tendency in human nature seems to evince itself in the press too, this is not a trait to be found among a narrow sect on the margins. There are constant stories about “genes” for a broad behavioral category. The journalists, let alone the public, seem to believe that we will find the seat of intelligence, anger, anti-sociality and a host other traits in one or two genes. This is almost always not so. Most of these traits that are being “explained” are:
1) Polygenic (many genes impact them).
2) Often additive to the point where one gene contributes to less than 10% of the genetic heritability, and the genetic factor might be the cause of less than 50% of the variation within the population!.
3) Very different genes might lead to the same behavior in the population (follows from 1, but I wanted to be explicit).
The caveats keep on coming.
Solutions? From us:
1) I’ll be clearer and assume less.
2) I’ll be more cautious.
3) I’ll highlight non-genetic factors in phenotype X more strongly so that people don’t cherry pick (can’t).
4) I’ll try to think of the non-intuitive population genetic foundations that underlay some of the principles, which I might take as givens.
5) Instead of linking to definitions of things, I’ll try and define them in the text, so that those who forget to double-check the link will know what I’m talking about in the paragraphs that follow and not misunderstand.
From you:
1) Whenever you think “Nature vs. Nature,” do a “search & replace” with “vs. or and or times” (in other words, there are more operations than subtraction implied, addition in polygenic traits and multiplication in the gene-environment interaction for instance might be appropriate analogs).
2) Outside of highly lethal diseases like Cystic Fibrosis, abandon the simple dominant-recessive Mendellian Model in your head. If it’s a complex behavior, keep in mind that dozens of genes are likely tweaking the overall phenotype, that gene-environment interaction can amplify the magnitude of the expressed phenotype, and that epistasis, the interaction of different genes in the genome itself in producing a phenotype, might also occur.
3) Realize that probabilites are important, genetics is statistical, that the importance of various factors shifts from person to person, dependent on the variables themselves (environment, specific genes, etc.) and we are usually speaking of whole populations.
4) Framing is important, English both under-expresses and over-expresses points (usually depending on personal context). This is partially sloppiness noted above, but the problems are magnified by the filters readers use.
I could go on. The main point is that this isn’t particle physics. A neutron has a mass that equals a proton + an electron. A positron has a positive charge. The zoo of particle physics has precise definitions.
When we speak of “heritability” it can get confusing since there are two main definitions (and the common sense default one tends to cr
eep in without much noise). Many of the models we present or paradigms we are using are first aproximations and rough fits of highly complex phenomena. If we saturated our text with the real number of caveats, notations, etc. that come to mind, you might as well go read PubMed.
Best
Razib
Posted by razib at 02:17 PM
We talk about a lot of complex genetic traits. Many of them are only partially genetic of course, but because of their social importance (intelligence, anti-sociality, etc.) we feel it important to approach all angles, including the genetic one. But one thing seems to show up in the emails that I receive, and the conversations I have with friends who know of my interest in genetics.
Here is a recent email:
I have a question about color of hair , would you like to help me to answer ? Thanks you anyway.
I have seen a family which has 4 members. Father is a American . He’s blond hair.
Mother is a Asian. She ‘s black hair. They has 2 children. They have blue eyes. But they have different colors of hair. The first is a man. He has black hair. The second is woman. She has blond hair. May you expain for me why they have different hair colors, please !
Another (from a friend):
Someone told me that since I had dark hair/eyes that I would be able to get really tan or brown if in the sunlight. So I believed that for years until I tried last summer and i only got burnt and peeled.
Well, I told my hairdresser this and she told me the reason why I cannot tan is because my mother is a red-head. Is that true? Even though someone has really dark hair and eyes, he cannot tan if he has redheaded family? Most blonds tan better than I do. Thanks for your time
What am I to say? When we were kids in high school they showed us Punnett Squares which illustrate simple crosses between parents, like so:
| Mother | |||
| A | A | ||
| Father | a | Aa | Aa |
| a | Aa | Aa | |
Assume that “A” is the gene for dark hair, while “a” is the gene for blonde hair. All the children should then have dark hair, right (thinking back to the capital usually being “dominant”)? You got the test question correct if you said “Yes!” “A” could be converted to many things, but it is “dominant,” while “a” is recessive, end of story….
There are a few problems with this model.
1) More than one gene might influence the phenotype.2) They might not be on-off, but additive.3) The very definition of the phenotype might slant our perspective a bit.
(note that Mendellian genetics does serve as the building block for modelling polygenic traits, but the Punnett Square can get really out of hand when you have many genes)
There isn’t one “blonde” color, it is a range. Similarly, there isn’t one “dark” color (in hair). Rather, in the fashion of a continuous trait, like height or intelligence, where there is a spectrum, you have light blonde and black hair as normal ranges of the phenotype (though getting a aproximate normal distribution might be problematic if you sampled the world’s population and classified their phenotype from visual inspection, assigning a integer value to “how dark” the hair is-but perhaps not as difficult if you used a machine to sample the concentration of pigment). The phenotype is caused by the presence of melanin. To add to the confusion you need to include another dimension with hair color: red. So you have auburn, strawberry blond, etc. thrown into the mix. I have posted several times on coloration in human beings:
Red hair.Hair color in general.And I linked to this PLOS article on skin color.
I think in the near future we’ll get a handle on these genes. There is obviously great interest in this topic, the “skin color” article was the top-viewed on PLOS a few weeks ago.
Back to the emails. I feel uncomfortable about addressing them because I feel they want cut & dried answers, but this isn’t like asking the chance of having a Cystic Fibrosis child if both parents carry the CF recessive gene. They’re asking questions about more complex genetics, filtered through their own perception of the phenotype. What is blonde? What is light? And so on.
But here is what I would say….
1) Children have less melanin than adults
2) Women have less melanin than men3) Environment also affects hair color
Bruce Lee one once said his son Brandon was the only “blonde Chinaman” in the world. If you know what Brandon looked like as an adult, he had dark brown hair (which could be perceived as black). Most European blonde children become non-blonde adults. It stands to reason that a half-Asian “blonde” (again, “blonde” can be relative, I have met many self-described blondes who I would not describe as such) would have dark hair as an adult. A similar pattern can be seen with blue eyes (note that skin, hair and eye color are not tightly linked). The saying that “all babies have blue eyes” is dependent on parental phenotype. In my family, the saying would more appropriately be that “all babies are born white.” Though we have brown eyes at birth, our skin is white until we are 6 months to 1 year old (I once talked to a friend of Korean origin who thought that all babies were born with the Mongoloid blue spot, and I have been told that black babies do not develop kinky hair for a few months). Additionally, there are also other eye colors besides blue and brown. Hazel and green for instance can be confusingly classified sometimes. I have known a few people who are half-Asian (of various kinds, east and south) who have hazel and green eyes. If that is classified as “non-blue,” then blue can be confirmed to be recessive. If it is interpreted as a more continuous trait, it gets complicated. If it is interpreted as a color caused by a different gene, well….
You get the point. People look different at different ages. Men and women are affected by the different levels of testerone and estrogen. The coloration of South Asian field-workers is often black, that of the Brahmin caste is lighter, some of this is genetic, but some of it is environment. Gay men often have blonde tips (thank you fashion!). Surfers are often very blonde (thank you sun & chemicals).
As to my friend with the red-haired mother, the abstract linked in the red hair post indicated that heterozygotes for the “red hair” locii are more prone to sun-burns. Score one for genetics + experience.
To sum, we have a case here where people want cut & dried answers, like physics. All I can present are the odds. I can tell you how the whole population should behave, but individual cases are … individual cases. The term educated guess is very appropriate.
Finally, the abiding interesting in this topic is pretty interesting. Free time in the consumer class and preoccupation with aesthetics is surely part of it. But theories about sexual selection for blondism are really interesting in light of contemporary concerns. I think it is safe to say that “the substance of style” has always been around (in biology it might be re-termed the function of style)…. Posted by razib at 04:08 PM
Gay Jewish writer gives up sex with men. Here are some money quotes:
But Benkof concluded that being gay is a social construct not intended by God, thus ruling out his justification for man-on-man sex.
“Historians all agree that there is no evidence of a gay minority,” he said. “If that’s true, it means that God doesn’t make people gay. That doesn’t mean it is a choice, but a social construct.”
…
But he identifies as a bisexual who refrains from his desire for men.
Though the ex-gay profiled in the article is only marginally a conservative (note his policy positions), his conservatization on his homosexuality freely makes use of traditionally Ivory Tower terminology like “social construct.”
On bisexuality: Here is a quote from psychologist Michael Bailey (the page being quoted can be found via the link):
Although there are clearly men who call themselves “bisexual” and who have sex with both men and women, both scientists and laypeople have long been skeptical that men with bisexual arousal patterns exist. Kurt Freund, who invented penile plethysmoography, related that he was never able to find a subset of men who appeared bisexual in the lab.
I remained agnostic on this particular issue until confronted by the penile data point. After all, the cock does not lie.
Personally, I don’t understand why religious gays assume that if they are hard-wired that way than God must think that it’s OK, do they live in Leibniz’s best-of-all worlds or what? Some people are born with far more severe social and physical problems than a particular behavioral orientation-and no one assumes that God must approve of kids who are dwarfs, have missing limbs or a fatal disease.
Posted by razib at 08:34 PM
One thing that I’ve always noted, Communism was anti-racist and anti-religious. Today Russia is rather irreligious ("control-f" Russia), despite the modest religious revival during the post-Communist era. But articles about Russian racism abound (some of the stuff is reminiscent of pre-Civil Rights United States). I know this might be journalistic hyperbole, but I also recall that one reason the Afghans hated the Russians so much was because of rather unconcealed racism that many of the soldiers evinced[1]. The same pattern of low religious belief and racialist feeling seems to be found in many regions of Eastern Europe.
Addendum: Peter’s comments have made to revaluate how I presented the above point, I should have emphasized nationalism rather than racialism, the latter being an extreme subset of the former.
fn1. In college the manifestations of racism from European international students that I encountered, though rare, did have a strong relationship to longitude.
Posted by razib at 04:05 PM
One thing that sometimes annoys me is that humans have a tendency (and something I have to resist it myself) to have a “vitalistic” conception of things, that traits have some mystical holistic residence in human nature. To clarify, I will bring up something that often comes up in the message boards.
When we post on attractiveness, the fact that many people seem to be most attracted to “their own kind” is noted. Some people (mostly explicit racialists) will assert that this is “natural” and “inborne,” but don’t elaborate a model. Rather, it is as if each human being has a vital essence of “whiteness” or “brownness” that attracts the essences of other beings who are like.
Let us ignore the impact of the broader culture and what not. There is a string of logic that I think can illustrate why people have an “inborne” attraction to their own race, without implying a metaphysical “race soul.”
1) People are attracted to their opposite sex parent
2) People tend to have parents of the same race
3) If you parents have of the same race, you will be of their race
4) Your opposite sex parent is your own race, ergo, you will tend to be attracted to your own race.
The following assertions are open to dispute (I can think of plenty of other factors that contribute to this tendency, mostly to do with the past history of sexual selection within one’s lineage), but I wanted to be explicit in showing how we don’t need to appeal to mystical vitalism, like Steve Sailer’s definition of race, we can construct the chain of reasoning and evidence behind trends and patterns we see without too much mental taxation.
Posted by razib at 04:19 PM
I don’t post on politics that much. Frankly, I admit I know very little that most of our readers don’t, while I do read a large number of books & monographs on history, science and social science, my political knowledge is mostly from newspapers, websites, etc. In short, not much value added for me to blather. But….
godless does post on politics, so I realize this site’s political orientation is more determined by him, so I’ll offer some opinions & perspectives here so that people know where I stand. After all, though godless & I tend to be generally concordant on scientific issues, on politics we have our differences (example: he likes US-style first-past-the-post, I like post-World-War II German-style proportional representation).
I’m a libertarianish sort of fellow. The gov. governs best that governs least. But I’m also (now) a realist. I think there are certain cultural preconditions that libertarianism can flourish in. So I’m no longer a universalist libertarian. I don’t think revoking gun control in Africa will lead to peace as Jeffersonian Democrats rise up to take their liberties. No do I think that it is an accident of history that post-World-War II Japan has developed its own political path that has emphasized consensus and de facto one party rule.
Culture matters. So does theory. This might be obvious to many of you, but back when I was an evangelical libertarian, a few key premises ruled my universe, and those Rights of men were inviolable.
My personal political preference is to aim for smaller government. Recently this meant voting Republican, but I am starting to wonder if this is the proper move, seeing as how Bush seems disinclined to aggressively push this course (unlike the 94 Congress). The fact is libertarians are a small faction, and something like the Free State Project is probably the best we can aim for in the short term-while in the long term transhumanism (gods willing) will make it irrelevant.
On the other hand, socialism is very popular. In the United States it is a very mild form. It tends to take the form of redistributionism and government overseeing of certain benefits programs. In much of Europe it takes two forms, the "commanding heights" (gov. controls industries) and high taxation welfare states. The former seems to be in decline, while the latter is still strong.
Many Americans on the Right detest Europeans in their adherence to socialism. Some commentators argue that socialism was foisted on the masses by self-interested managerial elites. While on some issues, like immigration and the death penalty, there does seem to be some dictation by fiat from above, on the issue of socialism, I think today the term social democratic is very apt (the laissez faire of post-World War II German ordo-Liberalism was imposed from above from what I have read). The spirit of Thatcherism is weak in most of Europe. Those be the facts. Old style classical liberalism was a strong force (in my reading of history) only in the transition between the ancien regimes and universal sufferage, when the educated bourgeoisie pulled more weight than they do today (though the living standards of Europeans today far exceed those of 100 years ago, I still recall that many are still self-consciously "working class," despite their participation in the consumer class).
Socialism is popular[1]. Rightists in the United States should get used to it. In Japan it takes the form of crony capitalism and subsidies to local economies. Income distribution in Japan is levelled by enormous transfers of wealth from the center out to rural areas (as well as maintenance of rural rice farmers). South Korea has its chaebol system. Perhaps Taiwan, and especially Hong Kong can be seen as models based more on the United States (and Hong Kong has never had a real democracy for any period of time!). So, in the First World, socialism is popular. The people are always right…right?
But…it does not follow that we (Americans) should shed our self-conception as the shining exception. Instead of fulminating about Euro-socialism, we should focus on preventing our own nation’s decline into dirigiste. American is a special country. I do not believe in God, so I don’t think this has religious roots, but rather, special circumstances of geography & history came together to create a peculiar republic with peculiar institutions.
To each their own. Liberal democracy, the combination of democracy and sacrosanct individual rights, is precious and comes in various forms. We (Westerners, broadly speaking from Japan to Finland) should accept our differences as the products of different national histories and local circumstances.
We should all look to our own backyards, that’s what we know best! As for Sweden, they should definitely start tackling their own problems with their black skulls. Perhaps they’ll be a little more understanding of the foibles, fumbles and injustices that have characterized this multiracial nation for centuries (hell, Gunnar Myrdal can write a book on how to integrate the black skulls!).
fn1. It seems least popular in Europe in the east, for obvious reasons. Estonia and to a lesser extent the Czech Republic have had aggressively economically liberal governments.
Posted by razib at 03:32 PM
While we’re giving props to PLOS (and there are some good articles for this month up), check out BioMed Central, which also has a lot of open access material. This is a great time to be alive if you are interested in cutting-edge science!
Posted by razib at 04:27 PM
Deep breath…
In my last musings on the subject of IQ comparisons, I said (threatened?) that I might return to the subject of the Flynn Effect.
The political scientist James R. Flynn was the first to draw attention to the fact that average intelligence test scores in most industrialised countries have increased substantially over a period of decades (Flynn [1], [2] – see the references below). Before Flynn, psychologists had occasionally mentioned that IQs had risen (e.g. Vernon, p. 207), but showed remarkably little curiosity about the phenomenon, so Flynn deserves the credit for highlighting it.
Here I am interested in the questions: how large is the cumulative Flynn Effect? How long has it been going on? And is it still continuing?
A rise in mean IQ scores has been found in almost every period in every industrialised country where the question has been studied (for a few exceptions see Storfer p. 97). The rate of increase is usually between 2 and 4 IQ points per decade, but rates as low as 1 and as high as 8 points per decade have been found. The largest increases are usually on non-verbal tests like Raven’s Progressive Matrices, the lowest on individually administered general tests of the Binet type.
Related interjection from Razib: Matthew Yglesias has a post on the black-white IQ gap.
The largest cumulative increases I can find in the literature are as follows:
West Germany 1954-1981: a 20-point gain by children on the German form of WISC [Storfer, p. 96]
France 1949-1974: 20-25 points gain on Raven’s among military recruits Storfer, p. 96]
Netherlands 1952-1982: 20 points gain on Raven’s among military recruits [Storfer, p. 97, cumulating the growth rates for three periods]
Japan post-WWII: 20 points gain over a 24 year period on Japanese version of WISC [Storfer, p. 99. From Storfer’s account I infer that the period was from the early 1950s to the mid 1970s.]
USA 1918-1995: Flynn, in Neisser (ed.), p. 37, gives a figure of 25 points for the increase in Binet-type (Stanford Binet or Terman-Merrill) test scores over this period.
UK 1900-1992: Flynn, in Neisser (ed.), p. 33, estimates that most Britons born in the late 19th century would have scored below an IQ of 75 on modern norms for Raven’s, implying an increase of 25 points or more over this period (see below.)
How far back does the Flynn Effect go? IQ tests only began around 1905 (Binet-Simon) and adequate national standardisation samples are not found until the 1930s. However, Flynn (Neisser, p. 36) gives evidence that the rising trend in the USA started no later than 1918. He also presents intriguing data from the Raven’s standardisation samples in the UK. The 1942 standardisation sample included adults aged up to 65 (and thus born from 1877 onwards), and Flynn concludes that even after allowing for decline of IQ with age, 70 per cent of Britons born in the late 19th century would have scored below an IQ of 75 on current (1990s) norms. This implies a mean IQ of not more than 70 on current norms [see note 1].
Is the increase still continuing? There is conflicting evidence on this. Lynn and Pagliari found that in the USA the rise continued unabated at least until 1989. However, Teasdale and Owen’s [2] study of Danish army recruits suggests that the rate of increase is slowing down, and is now ‘modest’.
If we assume that gains have continued in recent years at a rate of 2 points per decade, then the cumulative figures given above can be updated to give total gains up to 2002 as follows:
West Germany 1954-2002: 24 points
France 1949-2002: over 25 points
Netherlands 1952-2002: 24 points
Japan 1950-2002: 26 points
USA 1918-2002: 26 points
UK 1900-2002: 30 points or more.
I’m sure you can guess where this is leading to! By subtracting the cumulative ‘Flynn Effect’ from today’s IQ levels we can estimate the average IQ levels (by today’s norms) of these countries at relevant dates in the past. These levels can then be inserted for comparison into the table of national IQs provided by Lynn and Vanhanen. Here is the result, for selected industrialised and other countries (historic figures are in bold, the others are current figures as given by Lynn and Vanhanen [see note 2]).
Japan……………………105
Germany……………….102
Netherlands…………..102
UK………………………..100
USA (white)…………..100
France…………………….98
USA (all races)………..98
Czech Republic……….97
Greece…………………….92
Malaysia…………………..92
Indonesia………………….89
Iraq…………………………..87
Mexico……………………..87
USA (blacks)…………….85
Egypt………………………..83
India………………………….81
Guatemala………………..79
Japan (1950)……………79
Netherlands (1952)…..78
Zambia……………………..77
Germany (1954)……….76
USA (white, 1918)…….74
Uganda…………………….73
Congo (Braz.)……………73
France (1949)…………..73 or below
Jamaica……………………72
UK (1900)…………………70 or below
Nigeria………………………67
Sierra Leone……………..64
Equatorial Guinea………59.
I won’t consider in detail the causes of the Flynn Effect, which are discussed in detail by the contributors to Neisser (ed.). Personally, I like the argument of Richard Lynn that the main factor is improved nutrition during development and early childhood. Over the last 100 years, industrialised countries have seen three striking trends: (a) average height has increased; (b) the average age of puberty has fallen; and (c) average IQ scores have risen. Improved nutrition is the major reason for (a) and (b), so it would be a parsimonious explanation if it is also responsible for (c). But whatever the causes, they are likely to be environmental factors which vary between populations separated in space as well as in time.
Some of the cumulative increases in IQ (up to 30 points, or 2 standard deviations) may seem very large. Flynn himself describes them as ‘massive gains’. This may be somewhat misleading. We usually have no basis for judging the ‘size’ of an IQ interval other than the proportions of the target population who achieve the scores defining the interval. This is quite different from the measurement of physical qualities such as height, where (barring scruples about relativity) one inch is the same as any other inch. Nor is a difference of one standard deviation necessarily ‘large’ in relation to the total range of intelligence. Consider the analogy with height. In the late C19 the average height of mature males in England was about 5 feet 7 1/2 inches, with an s.d. of about 2 1/2 inches. Since then the average height has increased to 5 feet 10 inches, i.e. by about one s.d. of the C19 level. This is a noteworthy increase, but I don’t think anyone would be tempted to call it ‘massive’, since we can see (literally) that it is only a small proportion of total height. It should also be noted that a ‘large’ increase in IQ may boil down to a small number of items passed in a test. Each correct answer on Raven’s Matrices accounts for two IQ points, so an increase of 20 points corresponds to an additional 10 correct answers, out of a maximum of 60 items. Or in the Danish military tests, the total increase of 10 IQ points between 1958 and 1998 corresponds to a raw score increase of about 6 items out of 78 (Teasdale and Owen [1]). Is this ‘
massive’? What do such terms mean in this context?
Finally, an increase in mean scores does not necessarily mean that the whole distribution of scores has shifted upwards, retaining the same ‘shape’. Unfortunately the literature on the Flynn Effect tends not to say much about distributions. The studies by Teasdale and Owen are an exception. T & O [1] shows a marked change in the distribution. There is a reduction in the number of low scores and an increase in the number of moderately high scores, but no marked increase in very high scores. The distribution changes from symmetrical to negatively skewed, with a ‘pile-up’ of moderately high scores. T & O consider, but reject, the possibility that this is an artificial ‘ceiling’ effect. If this pattern is representative of the changing pattern of IQ scores generally, it might explain why we do not seem to be living in a golden age of genius.
Note 1: here I assume an approximately normal distribution (small departures from normality do not matter for this purpose) and a standard deviation of at least 10 points. Since the upper 30 per cent of a normal distribution are at least half a standard deviation above the mean, on these assumptions the mean must be at least 5 points below the boundary of the upper 30 per cent, hence if this boundary is 75 points the mean is not more than 70 points .
Note 2: I have simply subtracted the cumulative Flynn Effect from the ‘current’ IQ levels shown for these countries in Lynn and Vanhanen. In fact, L & V’s data are not all recent; e.g. their IQ of 72 for Jamaica is based on data from 1962. L & V’s procedure (p. 197-8 of their book) is to express each country’s mean IQ by reference to a mean IQ of 100 for the UK. If the test concerned was standardised for the UK substantially earlier or later than the date of the test in the other country, then L & V assume that mean IQ in the UK has increased by 2 points per decade, and adjust the data accordingly. For example, if country A had a mean IQ of 105 in 1970, on a test standardised with a UK mean of 100 in 1960, then L & V would estimate the UK mean as 102 in 1970. As this is 3 points below country A at that date, their table would state the IQ of country A as 103 against a notional UK mean of 100, preserving the differential of 3 points. Bizarre though L & V’s approach may seem, it is probably legitimate for combining data from different time periods, if you are going to do this at all. Provided that the mean IQs in country A and in the UK have increased at roughly the same rate since the date of the tests, the rank order of national IQs will be unchanged, and the numerical intervals will not be badly distorted (across the range of difference likely to be encountered in practice). If on the other hand mean IQs have increased at very different rates, then the figures in the table could be misleading with respect to current (2002) relative levels. However, this is unlikely to be the case for the industrialised countries considered here, because (a) most of the test data for these countries are quite recent, and (b) the rates of change in recent decades are unlikely to have been widely different in different industrialised countries.
References:
James R. Flynn [1] ‘The mean IQ of Americans: Massive gains 1932 to 1978’. Psychological Bulletin, 95, 1984, 29-51.
James R. Flynn [2] ‘Massive IQ gains in 14 nations: what IQ tests really mean’. Psychological Bulletin, 101, 1987, 171-91.
R. Lynn and C. Pagliari ‘The intelligence of American children is still rising’.
J. Biosocial Science, 26, 1994, 65-67.
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