Science in Black and White by Alondra Oubre

Author:Alondra Oubre
Language: eng
Format: epub
Publisher: Prometheus
Published: 2020-02-06T00:00:00+00:00

CHAPTER TEN

Smart Genes, Big Brains, and Civilization

IQ-LINKED GENES: THE SAGA IN A NUTSHELL

IF DNA IS THE BLUEPRINT OF LIFE, THEN MUTATIONS, OR CHANGES WITHIN DNA, are the driving force behind evolution, including adaptation to new niches, as well as the survival of a population or species. In chapter 9, we explored several pivotal genes reportedly linked with IQ. Since the search for the DNA underlying human intelligence began, the last three decades have witnessed the rise and eventual fall of multiple candidate genes purportedly involved in human cognition. Numerous gene variants have been tentatively associated with intelligence, but even when a genetic trait has been shown to contribute to IQ, the strength of that contribution is so small that it is often barely detectable. Variation in DNA comes from multiple sources and includes genetic changes that range from single nucleotide polymorphisms (SNPs), to insertions or deletions of sections of DNA, to movement of one part of DNA to another part, to chromosome mutations.1 A SNP—a variation in a single DNA building block, or chemical letter—is the most common type of mutation and increasingly used to help identify a person’s risk of developing certain diseases. SNPs also play a role in cognitive performance, sometimes either raising or lowering a person’s IQ score, depending on which gene variants have IQ-linked SNPs. Several candidate genes, including multiple SNPs, are thought to influence brain size or cognitive performance, or both. FADS2, a variant of a gene involved in reproduction, initially appeared to increase IQ in people who were breastfed, but later studies have contradicted this finding.2

In the last chapter, we noted that in a recent study on the genetics of cognitive ability, only three out of 69 candidate genes were implicated in increased intelligence. Each of these three variants was responsible for raising an IQ score slightly less than one-third of a point.3 For the majority of genes associated with cognition or social behavior, gene expression—the way in which a trait like smartness manifests—relies to some extent on the interactions between different genes and between genes and environment. Despite notable advances in clarifying the genetic underpinnings of intelligence, experts have yet to demonstrate that specific individual genes are responsible for a substantial portion of a person’s IQ, regardless of whether his score is at, above, or below the norm. Most importantly, to date, no one has pinpointed specific gene variants that are irrefutably responsible for differences in average IQ score across diverse ethnic populations.

The scarcity of SNPs firmly connected to intelligence performance may be comforting to antihereditarian, pronurture supporters who view ethnic differences in IQ through a lens of environment and experience. For some experts, the majority of gene candidates once considered crucial in the race and IQ debate have been debunked and dismissed as unviable prospects for the biology of intelligence. This does not negate the existence of IQ-linked genes, however. As neuropsychologist Christopher Chabris points out, the failure to find genes linked with g, or general intelligence, does not mean that g has no genetic basis.

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