(continue from your brain and your life)

Although the concept the race is a social construct which has conveniently been hijacked by naïve people as a “shorthand” to refer to groups originated from different geographical areas (ref. my post on “racism in the genomic era”) . Nevertheless, for the sake of debating, I here succumb myself to this “shorthand”. This does not mean I agree with this definition of race.

The controversy on racial IQ difference practically stigmatizes blacks. They have been labeled as “less intelligent” which is certainly not a pleasing description. But how much “stupidity” they are? Are they really THAT dumb?

The assertion that blacks are less intelligent than whites can be traced back to the time of American founding fathers when black slaves were discounted during the population poll and thought as half-human-half-animals. Early studies showed that the average IQ was 85 in African American and 70 in sub-Saharan African which was at the level of moron. In comparison, the East Asians had an average of 106, and whites had 100 in IQ test. This order was confirmed among different population, at different times, and using different IQ measurements. This pattern of 1.1 standard deviation difference persisted from childhood to adulthood despite IQ increases with physiological growth. Even at highly educated level, blacks on average had lower IQ score than their white peers.

In addition, during last fifty years, the black-white gap in IQ measurements in the United States has narrowed, but the large difference persists. The Head Start program, aiming to improve education for kids from poor family (blacks are disproportionally represented), hasn’t yielded many benefits. Studies found that despite the significant effects on these kids appeared in earlier age, the effects didn’t last long. It seems that blacks are doomed.

Because IQ tests rely on responders’ linguistic skills and are also affected by culture differences, objective measurements are more desirable. Reaction time measures the speed of response on simple questions and presumably reflects the neurophysiological efficiency in the brain, thus providing more accurate assessment of intelligence. Using this measure, blacks still showed far slower reaction time than East Asian and whites. Intelligence scores summarized from different reaction time measurements reached the same conclusion. There is no hope here either.

Brain volume, either measured in old fashion such as size and weight, or using fancy techniques such as magnetic resonance imaging (MRI), suggested that blacks had smaller brains than whites, while East Asians had the largest brains. Larger brain may have more brain cells and nerve connections. It may be more sophisticated to do mental work.

Given numerous consistent findings that blacks are not as smart as whites, it seems that at least there is a racial difference in IQ related intelligence. It is a plain fact, no doubt about it.

Well, I agree that there is a racial difference in IQ. However, how these “objective” measurements relate to intelligence is questionable. The correlation coefficient between IQ and MRI brain volume is about 0.40; and it is even far less between IQ and head circumference measures. The correlation coefficient between IQ and intelligence index from multiple reaction time measurements is at most 0.67. Quantitatively, they are not much.

Further, the logic of the evidence goes like this: IQ is positively related to brain volume; blacks have smaller brains than whites; then it must be true that blacks have lower IQ than whites In fact, the logic is false. Among studies Rushton cited in his review, most are unrelated studies and didn’t measure brain volume and IQ simultaneously among blacks and whites. They are irrelevant to answer whether brain size difference causes IQ difference between blacks and whites. In his study which indeed measured IQ and head circumference among 50,000 children, he only examined the relationship between cranial size and IQ in Asian children, but used the above logic to extrapolate his racial idea. An appropriate analysis should examine whether there is an interaction between cranial size and race in relation to IQ, ADJUSTED for potential confounders such as socio-economic status, family influence, and educational characteristics. Unfortunately, all of his cited studies during above discussion fell into “correlation or exploratory” studies with no careful adjustment. The correlation analysis can’t answer any causal factors.

As I have pointed out in the last post, studies following up people for some time, in particular those experimental studies can shed light on the causes of racial difference in IQ. To answer whether the cause is genetic or not, studies such as twin studies or adoption studies are particularly useful. They not only explore the genetic and environmental interaction, but also follow up the subjects for a long time to trace the IQ changes with education. They are also superior to common family studies in that the twin or adoption studies have an element of “natural experiment” which is desirable in dissecting cause and effect relationship.

To be continued….