Is it true that intelligence is inherited from the mother? originally appeared on Quora - the knowledge sharing network where compelling questions are answered by people with unique insights.
Answer by Drew Smith, Ph.D. in Molecular, Cellular and Developmental Biology, on Quora:
The first rule regarding new studies of the inheritance of intelligence is to be very suspicious of all studies of the inheritance of intelligence.
The history of these studies is not a happy one. Stephen Gould wrote a whole book (The Mismeasure of Man) detailing all the ways in which biological research has been co-opted in the service of racism, misogyny, homophobia, and economic repression. Intelligence research, not surprisingly, has always been one of the worst offenders.
The whole field suffers from foundational weaknesses: we cannot really define intelligence, and we cannot separate it from culture. Psychologists do indeed have definitions of intelligence but (surprise!) these definitions tend to emphasize skills at which psychologists excel, like verbal fluency and manipulation of abstract symbols, for example. A cynic might add to this list a willingness to believe that results from experiments on affluent Western undergrads can be generalized to the rest of humanity.
That said, there is little doubt that there is a heritable component of intelligence. Whatever forms intelligence might take, it is ultimately about problem solving, and the best problem solvers are the ones who live to reproduce. Although the idea of genes "for" intelligence is a fallacy, there are many genes that function to affect intelligence. The survival value of different alleles of these genes is highly dependent on environment, not least the societal and cultural environment in which they operate. Few, if any, of these alleles make their bearers more intelligent. They are instead likely to affect the forms that intelligence takes.
It is not remotely plausible that all of the genes that affect intelligence are inherited from the mother, but that is not what the linked research claims--rather, it claims that a preponderance are. There are a few mechanisms by which this could happen:
- A number of genes that affect intelligence could be located on the X-chromosome. Since males have only one X chromosome, which is inherited from their mothers, their intelligence might be more closely linked to their mothers than to their fathers.
- Genetic imprinting can cause genes inherited from one parent to be preferentially suppressed. This seems to be what the new research is claiming. Although this is plausible, I'd wait for a few more confirmatory studies before accepting it as fact.
- Mitochondria are inherited (almost) exclusively from the mother. Though mitochondrial genes might not seem to be genes related to intelligence, brains are voracious consumers of metabolic energy, which is supplied by mitochondria. Better mitochondria are likely to translate to better brain function.
A lot of the research cited in the articles claims to show that children's intelligence is more closely correlated with that of their mothers than with that of their fathers. Well, duh. So long as mothers are the primary caregivers, they are also the primary architects of their child's environment during the period of critical brain development. Of course smart mothers tend to raise smart children. Raising children to be good problem solvers is itself a problem to be solved, and mothers with better brains are likely to do a better job of it.
The genetics of intelligence is one of the LaBrea Tar Pits of science. It is covered with the sticky tar of subjectivity, and is still struggling to climb out of the tar and onto a firm, objective footing.
Photo by Daniel Schwen, own work, CC BY-SA 2.5
Footnotes
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