Toward a Molecular Biology of Human Intelligence: Psychometrics Meets Gene Expressions and Brain Metabolism

IQ Research
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The ICA Journal has a new article by Richard Haier about the connections between IQ scores, genes, and brain functioning (with some evolutionary biology and environmental influence thrown in, too).

Article 1
Article 1973×811 95.9 KB

It’s an information-packed article that connects findings from different branches of psychology, neuroscience, and biology to show (1) how humans evolved such smart brains and (2) the biological process that connects each individual’s genetic blueprint to brains that show individual differences in intelligence.

Here are some highlights:

:right_arrow: Regions of the brain that have experienced large changes in recent evolutionary history seem to be more important for intelligence.
:right_arrow: There has been a evolutionary tradeoff: in exchange for a larger, smarter brain (and enhanced regions of the brain), the brain has been more hungry for energy. Balancing these two conflicting demands has been an evolutionary tightrope that humans seem to have walked.
:right_arrow: There are specific genes (discussed in the paper) with common variants that are very likely to have biological functions that result in smarter brains. The function of these genes are understood, and though their relationship with IQ is modest, they give us important clues into how genes result in smarter brains. (After all, the genes don’t whisper the answer to an IQ test question into your ear. Any impact they have on IQ must be via biology.)
:right_arrow: Fetal development seems to be fine tuned for building a smart brain (under normal conditions), especially in the timing of uptake of polyunsaturated fatty acids during the third trimester.

There is a lot more in the article. It doesn’t answer every question about how intelligence develops (either in the species at large or in individual humans), but it pulls together a great deal of interesting evidence in one place.

Link to original post: https://x.com/RiotIQ/status/1986804835132330077?s=20

Full article: https://doi.org/10.65550/001c.146520

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Haier’s doing important work bridging the gap between psychometric g and actual biological mechanisms. The evolutionary tradeoff angle is particularly compelling - brains got smarter but became metabolically expensive, so we’re walking a tight energy budget. The focus on HARs (Human Accelerated Regions) and precuneus involvement gives concrete targets for understanding how genes → biology → cognition. This kind of integrative framework is what the field needs to move beyond just describing correlations.

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This is the kind of synthesis work that moves intelligence research forward. Rather than staying siloed in psychometrics or molecular biology, it connects evolutionary pressures, specific genetic variants, brain metabolism, and developmental timing. The third-trimester PUFA uptake detail is fascinating - it suggests critical windows where environmental factors could matter most. The challenge now is translating these insights into testable predictions about individual differences that go beyond what we already know from behavioral genetics.