In this Topic, I will argue that research on race, brain size and IQ constitutes a significant line of evidence that supports a genetic model of racial differences in IQ. But before we turn to that topic directly, we need to differentiate phrenology research from brain size research. Phrenology was largely concerned with predicting people's psychological traits using the bumps and curves of their skulls. Empirically, this has been shown to be invalid (1). In contrast, meta-analyzes consistently show that brain size is positively correlated with IQ.
In addition, a 0.19 correlation between brain volume and fluid intelligence was found in a pre-recorded analysis of 13,608 Britons (7). The fact that this study was pre-registered implies that the publication bias cannot explain the finding.
Other evidence:
1) Several studies have shown a genetic correlation between IQ and brain size (including what I will still cover in the second part of my text). This means that the same genes that explain the variation in IQ also explain the variation in brain size (7, 8 and 9) The simplest explanation for this finding is that some genes influence IQ by influencing brain size.
2) The size of people's brains changes throughout life. Studies looking at the same people over several years show that changes in brain size predict changes in IQ (10). In addition, brain size and IQ follow the same pattern of life expectancy (11), increasing until the age of 20 and decreasing markedly in old age (12). The simplest explanation for these findings is that changes in brain size over time cause changes in IQ over time.
3) Breeding experiments that create animal populations to be more intelligent also end up creating animals with larger brains. For example, one study created mice for 12 generations to be better at finding their way through mazes and said that mice ended up with brains 2.5 standard deviations greater than those of the first generation (13).
and where does the breed come in ?:
In 1994, the first study was carried out (14) comparing the brain size of different racial groups using MRI technology to measure the size of the brain. They confirmed previous findings: blacks have smaller brains than whites.
the case of genes:
The most plausible explanations for this situation are
1) Environmental pressures: people who lived in freezing climates had to have a greater coginitive demand to prepare for severe winters. Brains in a cold climate can lead to a substantial increase in the brain because, in such conditions, a larger brain would be better at maintaining a constant temperature in its core. I believe that cooked meat is also related to a certain degree, but that is a topic for another topic
2) Genetics: currently more than 500 specific alleles linked to intelligence have been discovered, the majority of which are related to the size of the brain, more specifically the CASC5 Gene was found in Asian peoples and the MCHP1 or "microcephaline" in Europeans. A detail is that sub-Saharan African peoples do not have these genes mentioned above, which corroborates the low black IQ. Recent advances in genetics are consistent with this point of view. For example (15) analyzed racial differences in 9 IQ-related gene variants and found that whites were more likely than blacks to have the high IQ-related variants of all 9 genes. East Asians were also more likely than whites to have the high IQ-related gene variant in most cases. In (16) provided more direct genetic evidence when analyzing data in 101 countries and found that the more genetically different two populations, the greater the IQ difference between them. Another variable that predicts regional cognitive ability is the average degree of mixing of White in a population or, in other words, the degree to which the average person is genetically European. (17) found that this is the case in data sets in American nations, states within Latin American nations, such as Colombia, Brazil and Mexico, and in states in the USA. Research has also repeatedly shown that mixed race individuals have IQ scores between their parents' average race scores (18) and (19) a study also found this to be true for mixed race blacks who mistakenly believed they were all black (20)
obvious environmental causes. will be?
at this point, surely you must be asking, and the environmental causes, such as socioeconomic status, education, racism? These questions will be answered here, first of all, I must point out that yes, some things like a poor diet in childhood, or growing up in a dirty environment can indeed influence your IQ making you not use all your genetic potential, but the disparity it's not that big, being -7 points, in the end it doesn't change much. That said, here are the answers to those questions.
1) poverty: Poverty correlates with IQ, but the control of socioeconomic status, whether measured by parental income, education, neighborhood, wealth or otherwise, does not close the IQ gap between blacks and whites. This has been demonstrated in more than 60 studies over the past 100 years (21) In fact, poor whites do better on standardized tests than rich blacks.
2)"What about single motherhood?" Even when just looking at people from two parents' homes, the Black-White IQ gap persists (22) (23) Furthermore, research has shown that the IQ gap between blacks and whites and between whites and East Asians still it exists even when looking only at people raised (through adoption) in white homes (24), that is, two birds in one stone.
3)"What about education?": Another possibility is that differences in access to education cause the IQ gap between blacks and whites. This is not possible because the IQ gap between blacks and whites exists at the age of 3, which is prior to the beginning of formal education (25) In addition, the IQ gap between black and white remains after controlling parental education ( 26) (27) In addition, blacks with graduate degrees score worse than whites without a four-year diploma in cognitive ability tests (28) So clearly education is not the cause of racial cognitive differences.
"4) "What about racism?": Finally, let's look at racism. To affect intelligence, racism must affect blacks through some concrete mechanism. As we have seen, the racism that makes blacks poorer, less educated or more likely to live in homes with only one parent cannot explain the difference in IQ. Another possibility is that racism has led blacks to internalize negative stereotypes about their intellect, which in turn impacts their performance on the tests. This hypothesis is refuted by the fact that blacks have higher scores than whites on measures of general self-esteem and are more likely than whites to describe themselves as more intelligent than the average (29)
Final considerations:
Finally, we can point to the IQ B / W gap as being a genetic and / or partially genetic cause.
