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In spring 1998, Robert Plomin claimed to have discovered a gene linked with intelligence. More recently, the Human Genome Project was cautious when approaching areas implying racial differences since research actually shows greater genetic differences within races than between races. However, not all individuals are endowed with the same intelligence and many believe this must have something to do with our genes and the way they interact with the environment. Identical twins are more likely to obtain the same score in an IQ test than twins from two separate eggs that have a different genetic make- up.

It is important to remember that genes work by interacting with the environment, so social factors will also infl uence intelligence. Intelligence tests may be more of an assessment of social factors, such as your educational background. Black children adopted into white middle-class families score signifi cantly higher on average than those in working-class families – implying a cultural slant to tests.

My classmate thinks that this article suggests that race is suggested as determining intelligence, because race is mentioned several times in the article as being linked to intelligence, whether genetically or through social factors. I want to check this before confronting her, but I think not. Who's right?

In my view, the first bolded sentence dismisses race as a determinant, because there are 'greater genetic differences within' each race than between different races.

The second bolded sentence also rejects race, because it only shows a cultural slant to tests and the first sentence of the last para states 'social factors will also infl uence intelligence.'

Source: ‘Are you born brainy?’, 17 November 2004, from BBC News at www.bbcnews.com

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    $\begingroup$ This is kind of like when you compare men and women: in almost all cases, any statistically significant differences between the groups are rendered utterly insignificant when you consider variability within the groups. So yes, both bold sentences are what you should emphasize in your discussions with your friend. $\endgroup$ – user6682 Sep 26 '14 at 20:57
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    $\begingroup$ "Identical twins are more likely to obtain the same score in an IQ test than twins from two separate eggs that have a different genetic make- up." That's an amusingly convoluted way of saying "Twin's IQ scores are highly correlated". $\endgroup$ – jona Sep 28 '14 at 9:13
  • $\begingroup$ There is greater variation of height within the set of men and the set of women, than between the average of the two sets. Yet, the average height of women is lower than the average height of men... When will we wake up and realize that every single person is simply different from every other person, despite having things in common with many of them? Why must this be a problem for anyone? Why do we need an explanation for observed tendencies? What is the point of seeking the explanation? For height, well, people survived better when men got bigger. For intelligence... (over to you) $\endgroup$ – user9634 Sep 30 '16 at 13:20
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The relationships between race and IQ is a sensitive topic for many good reasons. It also raises a lot of deep questions about how to assess the role of genetics and environment.

A good summary of the literature on Intelligence with a discussion of racial differences can be found in the article "Intelligence: Knowns and Unknowns" (FREE PDF).

Within-group versus between-group variance

You write:

In my view, the first bolded sentence dismisses race as a determinant, because there are > 'greater genetic differences within' each race than between different races.

Group differences can be quantified. They are often quantified in psychology in terms of cohen's d (i.e., the size of group differences in terms of the standard deviation). You sometimes hear the claim that within group differences are larger than between group differences. This point is often highlights that just because a group on average is higher on a variable, there is a large proportion of people in the lower group than are higher than people in the higher group. The claim is often made to remind people not to stereotype. However, from a scientific perspective, we are often quite interested in the size of the difference between group means and the causes of such differences.

Importantly, group differences need to be very large before between-group variance is larger than within group variance. A grouping variable can have an effect of an outcome variable without needing to achieve this degree of group difference.

The size of the group differences says very little about whether the effect is causal.

Race as cultural slant

The second bolded sentence also rejects race, because it only shows a cultural slant to tests and the first sentence of the last para states 'social factors will also influence intelligence.'

I don't think the second bolded sentence entirely rejects race. However, the wording "cultural slant" does go some way towards this argument.

However, I'd challenge the "cultural slant" argument. In particular, if some environments lead to higher IQ, I would be more inclined to interpret that as an effect of environment on IQ rather than saying that IQ tests have a cultural bias. You might argue that the kind of intellectual functioning represented by IQ tests is more valued by some cultures, but that's quite different. Once you operationalise IQ in terms of a general factor that emerges from a wide range of cognitive ability measures, then it makes sense to proceed with this. This is the variable that has been validated (i.e., predicts educational attainment; entry into prestigious professions; job performance particularly in cognitively demanding job; future income; etc.)

Also, to show that environment influences IQ is interesting, but it does not refute the role of genetics. Researchers in this space (e.g., looking at twin studies) often aim to estimate the proportion of variance in IQ due to environment and genetics. To show an effect of $A$ does not mean that there is not an effect of $B$.

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  • $\begingroup$ Which causes what? that's what I want to know. Which, is never going to get resolved, because it is all entangled anyhow. $\endgroup$ – user9634 Sep 30 '16 at 13:21

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