HBD: Human Biodiversity

More Evidence of the Heritability of IQ


The group of Paul M. Thompson at UCLA recently published a paper in the Journal of Neuroscience, "Genetics of Brain Fiber Architecture and Intellectual Performance," in which they reach the following conclusions.

We visualized the anatomical profile of correlations between white matter integrity and full-scale, verbal, and performance intelligence quotients (FIQ, VIQ, and PIQ). White matter integrity (FA) was under strong genetic control and was highly heritable in bilateral frontal (a2 = 0.55, p = 0.04, left; a2 = 0.74, p = 0.006, right), bilateral parietal (a2 = 0.85, p < 0.001, left; a2 = 0.84, p < 0.001, right), and left occipital (a2 = 0.76, p = 0.003) lobes, and was correlated with FIQ and PIQ in the cingulum, optic radiations, superior fronto-occipital fasciculus, internal capsule, callosal isthmus, and the corona radiata (p = 0.04 for FIQ and p = 0.01 for PIQ, corrected for multiple comparisons).

Note that for the bilateral parietal lobe, the correlation for heritability was .85, meaning that 85% of the variation seen in white matter integrity among individuals is inherited. This part of the brain is involved with visio-spatial skills, logic, and mathematics.

The paper also states:

In a cross-trait mapping approach, common genetic factors mediated the correlation between IQ and white matter integrity, suggesting a common physiological mechanism for both, and common genetic determination. These genetic brain maps reveal heritable aspects of white matter integrity and should expedite the discovery of single-nucleotide polymorphisms affecting fiber connectivity and cognition.

Arden et al. Recently published a paper that sheds some light on this: "Intelligence and semen quality are positively correlated." They find that, controlling for “age, body mass index, days of sexual abstinence, service in Vietnam, or use of alcohol, tobacco, marijuana, or hard drugs”, sperm concentration, count, and motility were modestly correlated with intelligence in a sample of American military veterans, suggesting that some common factors are involved. Since the variables that they controlled for are in turn correlated with health, it would seem that the correlation between semen quality and intelligence does not arise from the state of health affecting both semen and brain. Rather, the correlation might be genetic, perhaps a “phenotype-wide fitness factor”. A more recent paper, "Why is intelligence correlated with semen quality? Biochemical pathways common to sperm and neuron function, and their vulnerability to pleiotropic mutations," the same group discusses the common biochemical pathways of neurons and sperm.

Potentially, such pleiotropic mutations could produce positive genetic correlations in the functional efficiencies of different organ systems, yielding positive phenotypic correlations in different components of fitness, such as intelligence and fertility.

In short, more evidence from neuroscience is emerging that intelligence is highly heritable and that the mechanism of inheritance may give rise to a general 'fitness factor”, or absence of harmful mutations. These results from biology continue to support the hypothesis of the heritability of intelligence, which has been known from the work of psychologists for a long time now.