Tag Archives: IQ

IQ Population Genetics: It’s not as Simple as You Think

IQ Population Genetics: It’s not as Simple as You Think

A paper I came across while blog surfing. While the IQ stuff is interesting, what really caught my attention was the section on the out of Africa date.

Both genetic evidence (Ingman et al., 2000; Underhill et al., 2001; Zhivotovsky et al., 2003) and the fossil record (White et al., 2003) point to Africa as the likely homeland of our species. According to the most widely accepted scenario, one or more subgroups of early modern humans left Africa between 120,000 and 100,000 years ago to become the ancestors of the non- African populations

Which makes a pleasant change after reading an idiot paper earlier today that was hitting the 40k date. Again.

 And something I didn’t know..

Genes, like drugs, have many side effects. This is called pleiotropy. For example, the average IQ of nearsighted people is 6 to 8 points higher than the average for normal-sighted people.

Although I am familiar with a medical condition called torsion dystonia that raises the IQ of the sufferer by an average of 10 points. An interesting read.

Brain size, relative intelligence, sex and fat.

After re-reading the ludicrous (and I’ll explain why it’s ludicrous) assertion that women have an average IQ five points lower than the male claims from Lynn, I thought I’d dig up some of the facts and figures surrounding this flawed work.

First of all I’m going to put a link to this paper on relative brain size and intelligence by Tom Schoenemann, a professor whose specialist field is the evolution of the human brain. It has several numbers relevant to this subject:

Male:          (55.5 kg body weight, 1361 g brain weight)
Female:    (51.5 kg body weight, 1228 g brain weight)

As you can see, the human male appears to have a brain size proportionally slightly larger than the female. However, one thing  routinely ignored in all these measurements is fat. The average human male  (Western) carries a body fat of about 16%, women carry about 22%. Which means you need to calculate the relative brain size compared to non-fat mass, as fat is a null factor and as far as anyone can tell requires no processing power to control. My IQ at nine stone would be exactly the same if I weighed ten stone, although my relative brain size would have decreased due to the extra fat I now carried. This does not apply to long-term obesity which affects the brain, but the mere gaining of a few pounds has no known effect on IQ.

So from the numbers above the  you would have 25.52 g of brain per kg of body mass (male) vs 23.84 g (female). The female comes out as 93.4% the relative size of the male from this.

Factoring in the difference in body fat… 

 male       55.5- 8.88 (16% fat)  =  46.62  for 1361g, or 29.19g/kg

female    51.5 – 11.33 (22% fat) = 40.17 for 1228g, or  30.57g/kg

And all of a sudden the ‘large relative difference’ (16.6% here) between male and female brain size does a vanishing act. Here women actually seem to have a slightly larger relative brain size, although this may well be from the body fat percentages I used here being slightly askew. I’m not claiming that the percentage for body fat is 100% accurate, and if anyone reading this can link me to a study with the exact figures I’d be grateful, but you get the ballpark idea here.

In the Lynn study he comments how women seem to be doing better than men in spite of having a lower IQ; which suggests to me that the tests he and his colleagues were using were hinky. One of the main uses for IQ tests is to predict academic ability, and really all that Lynn’s test did was establish that his did not measure academic ability well in women or men, which pretty much proved it was slightly biased in favour of the male, and therefore not an accurate measure of intelligence. Gender biasing an IQ test is easy to do if you put in a few extra maths questions and remove a few language questions (in favour of the male). Something similar happened in the early days of IQ testing when a series of IQ tests found women to have a notably higher IQ, until they ‘balanced’ the test out.

This really goes towards ‘what are IQ tests and do they measure general intellegence’ debate. So far (poll a few psychologists) the consensus is that IQ tests are a real indicator of your general intelligence level and are a good predictor of your life outcome. If they weren’t relevant to real life/academic success, the only thing an IQ test would indicate would be how good you are at IQ tests, and your score wouldn’t be even remotely related to how smart you are (see earlier point about the tests Lynn used).

Going back to the Schoenemann paper, he makes it very clear that so far relative brain size and IQ are very strongly correlated:

“It is quite simply a myth that brain size and  IQ are empirically unrelated in modern populations.”

So far all the studies I’ve seen show a correlation between general brain size and IQ of about .4, which is statistically significant. I’m wondering if a more focused MRI/IQ brain size study vs non-fat body mass would reveal a much higher correlation for humans than this.

But essentially, functionally identical relative brain size (when fat is factored in) for male and female makes Lynn’s claims for a 5 point difference extremely hard to support, even more so when he admits that the tests used did not accurately predict academic outcome for the women who took them. In fact, he himself has commented on how racial difference in IQ are supported by the difference in relative brain mass. So how, with no quantitive difference between sexes in relative brain mass, can his claims for a lower average female IQ be correct?

It can’t.

Shame on you for bad science, Dr Lynn.

Intelligence and birth order in boys and girls

Intelligence and birth order in boys and girls

 The relation between intelligence and birth order was shown in a recent publication [Bjerkedal, T., Kristensen, P., Skjeret, G. A. & Brevik, J. I. (2007). Intelligence test scores and birth order among young Norwegian men (conscripts) analyzed within and between families. Intelligence, 35, 503–514] to be negative. Subjects in this and in an influential earlier study [Belmont, L. & Marolla F. A. (1973). Birth order, family size, and intelligence. Science, 182, 1096–1101] were all men. We tested if the association of IQ and birth order is the same in men and women. Longitudinal IQ data were available from 626 Dutch twin pairs at ages 5, 12 and 18 years. The number of older siblings in these twin families was between zero and five, and was recoded into 3 categories (0, 1 and 2, or more). IQ data were analyzed with a model in which age cohort, number of older sibs, sex and all interactions were included as fixed effects. The dependency between twins was modeled as a function of additive genetic effects (A) and common environment (C) shared by children from the same family. Effects of A, C and unique environment (E) were allowed to differ as a function of age. The correlation across time between IQ scores was modeled a function of genetic and environmental factors. The test for the effect of N of older sibs was significant [F(2,827)=6.51 (p=0.0016)], while the interaction of N of older sibs with sex was not significant [F(2,933)=1.93, p=0.15]. Heritability for IQ was estimated at 37% at age 5 (C explained 34% of the variance). At ages 12 and 18 heritability for IQ was 81% and 82%, respectively. At these ages C did not contribute to IQ variation. We conclude that the dependency of IQ scores on birth order does not differ for boys and girls. We discuss these results in the context of the general findings of the absence of common environmental influences on IQ scores in the genetic analyses of adolescent and adult twin data.

On the quite I’m quite interested in IQ testing and studies. This has some information on the Hereditability on IQ with age; 37% at age 5, 82% at age 18. And as I recall it gets higher the older you get, in the 90% once you are a full adult living your own life. Which makes a lot of the IQ studies that have been carried out on children pretty much pointless, as their IQ’s are so plastic at that age.

Did nutrition cause the Flynn effect on IQ?

What has caused the Flynn effect? Secular increases in the Development Quotients of infants

Richard Lynn

aUniversity of Ulster, Coleraine, Northern Ireland, BT52 1SA, UK

Received 23 March 2008;  revised 17 July 2008;  accepted 17 July 2008.  Available online 21 September 2008.
Results of five studies show that during the second half of the twentieth century there were increases in the Development Quotients (DQs) of infants in the first two years of life. These gains were obtained for the Bayley Scales in the United States and Australia, and for the Griffiths Test in Britain. The average of 19 data points is a DQ gain of approximately 3.7 DQ points per decade. Similar gains of approximately 3.9 IQ points per decade have been present among pre-school children aged 4–6 years. These gains are about the same as the IQ gains of school age students and adults on the Wechsler and Binet tests. This suggests that the same factor has been responsible for all these secular gains. This rules out improvements in education, greater test sophistication, etc. and most of the other factors that have been proposed to explain the Flynn effect. It is proposed that the most probable factor has been improvements in pre-natal and early post-natal nutrition

More from professor Lynn; a bit of an ass at times, but not stupid. This suggests that most of the IQ gains made through the 20th century a mainly attributable to better nutrition (we are about 30 points smarter than we used to be in the Victorian era).

This would also be another kick in the teeth for the ‘environment only’ supporters who believe we are all born the same, but our IQ’s vary solely from environmental factors. Generally malnutrition isn’t common even among the poorest groups in the West, so this makes most IQ differences you see between individuals due to genetics. The current estimate of heritability is 70% ish, with most of the 30% being nutrition and infantile stimulation. I’d like to see a study of vegetarian/vegan children to see if they compare well to omnivores.

IQ and gender.

Hmm I’ve been reading up on IQ and gender on Wikipedia. Pretty funny really. If you know a lot about IQ tests and life outcome, it’s laughably simple to see how some of the mooks of this world will read SAT scores and university IQ tests as proof that women have a lower IQ, as the male average on all of these is a bit higher than female. The reason for the higher score is…drumr0ll… That most of the really low IQ people won’t be taking those test, and they are mostly men!It’s very simple, the lower the IQ, the more likely you are to drop out of school and not get around to sitting an exam that you know you’ll fail abysmally. If your IQ is less than 70 there is a 55% chance that you’ll drop out of high school, at 80 to 70 it’s 35%, at IQs above 120 it’s statistically insignificant (just me then). And the majority people with learning difficulties are male (about twice the number of women). It skews the numbers to make male IQ look higher. If you want to test a population to find the mean, you have to test ALL OF THEM. Anyone who understands statistics even a bit can see the bias.