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Genetics and Intelligence: IQ-Influencing Genes and Paths to Optimization

Key takeaways:
~ Researchers have identified hundreds of genes that influence IQ.
~ Intelligence is considered highly heritable.
~ Beyond IQ scores, genes also influence other forms of intelligence, such as musical ability.
~ There are many options for optimizing cognitive function, personalized for your genes.

Members will see their genotype report below, plus additional solutions in the Lifehacks section. Consider joining today 

Defining intelligence

General intelligence is a concept that encompasses abilities such as math ability, memory ability, verbal ability, and reasoning abilities. It is the sum of all of those things, not a single talent. The intelligence quotient, or IQ, is the score on a test that attempts to quantify general intelligence.

One research publication sums it up: “Intelligence can be broadly defined as the ability to learn, reason, and solve problems. It is a latent trait that cannot be directly observed but is inferred from a battery of diverse cognitive test scores, as in widely used ‘intelligence tests’ that yield a so-called ‘IQ score’….”.[ref]

IQ stands for intelligence quotient, and it is simply a test score used to quantify intelligence. Like any quantification of a broad concept, IQ scores have pros and cons and may not be an accurate representation of intelligence for everyone.

Intelligence scores are very stable once you reach adulthood. In children, though, intelligence has been shown to be more flexible, with interventions such as education, diet, and security of home life being shown to positively impact IQ scores at different ages.[ref]

More than just IQ:

Psychologists have proposed other ways of defining intelligence over the years. For example, Howard Gardner’s theory in the 1980s of multiple intelligences defined other ways of looking at intelligence, such as musical ability, kinesthetic intelligence, linguistics, ability to understand nature, and interpersonal or social intelligence.[ref]

Take musical ability as an example: Twin studies show that musical engagement, as well as pitch, melody, and rhythm discrimination, have a genetic component. Researchers have developed polygenic scores incorporating many different genetic variants associated with rhythm or pitch. Interestingly, rhythm, pitch, and musicality all go together when it comes to genetic components.[ref]

What can genetics tell us about intelligence?

Intelligence in adults is strongly genetic. It is estimated to be 60-70% heritable, showing a strong genetic component.

Interestingly, intelligence can change from childhood to adulthood. According to twin studies, genetics is only about 40% -50% responsible for intelligence in childhood, but it increases to about 60%-70% in teens and adults.[ref][ref]

First, let me make it clear that no single gene or even a handful of genes makes a significant difference in IQ. Instead, there are hundreds of genetic variants that make small differences. (The exception is rare mutations that cause genetic diseases with severe intellectual disability.)

Genome-wide association studies (GWAS) use large data sets, looking at the genomes of tens to hundreds of thousands of people. These large, high-powered statistical studies have made significant advances in understanding how genetics impacts intelligence.[ref]

GWAS studies are important for more than just identifying IQ genes. Understanding the genetic and metabolic processes contributing to intelligence can help researchers better understand cognitive decline in aging, temporary cognitive impairments, and social issues within education.

Looking at funding sources for some of the research on intelligence highlights an interesting issue: Some companies are developing apps that use genetics to predict IQ for children and to predict and guide educational outcomes. Personally, I think that is a slippery slope that we, as a society, shouldn’t go down.

Why are intelligence and genetics such controversial topics?

I knew coming into this topic that writing about intelligence and genetics was kind of taboo and controversial, but I really wasn’t completely clear on why… until I read a few of the studies from the 60s and 70s on the topic. They were very rudimentary in terms of understanding the genes involved, but they were also somewhat racist in their wording and conclusions. Those early ‘scientific’ publications were then expanded upon by other writers, claiming certain races were more intelligent than others.

To use a non-scientific term – it was a lot of bunkum.

However, the poor quality and manipulation of the initial studies have led to much higher quality research now. This review article explains how: “During the past century, genetic research on intelligence was in the eye of the storm of the nature-nurture debate in the social sciences. In the 1970s and 1980s, intelligence research and its advocates were vilified. The controversy helped raise the quality and quantity threshold for accepting genetic research on intelligence. As a result, bigger and better family studies, twin studies, and adoption studies amassed a mountain of evidence that consistently showed substantial genetic influence on individual differences in intelligence.”[ref]

Current research into intelligence and genetics still has ethical issues intertwined. There are questions on how intelligence is defined as well as some real issues involving how (or when) the research will end up being applied to children.[ref]

Just as genetics research on intelligence was used for racist or eugenics purposes in the 1960s, I believe there are legitimate concerns about current genetics research, which is light years ahead of what was thought in the 1960s, being used in more subtle, but still insidious, ways in education. I hope that using genetics to define educational pathways for children is never implemented, but I’m afraid it will be.

Genes that impact intelligence:

I’ll list the specific genetic variants below in the genotype report. Here, I want to explain the bigger picture — how the genetic variants linked to intelligence elucidate the pathways involved.

You have what you have when it comes to IQ genes. There is no changing what you were born with there.

However… Understanding the pathways involved is interesting and hopefully applicable to optimize areas where you may not have the optimal genetic combination.

Genome-wide association studies (GWAS) have figured out about half of the variants that explain intelligence. While GWAS studies are a great tool for detecting how common variants relate to a trait (in this case, intelligence), they don’t detect the impact of rare variants.

A recent genetics study determined most of the rest of the genetic components – the other half of intelligence genes – in a pretty cool way. The researchers used large data sets, which included genetic and family data for 20,000 people. The interrelated individuals allowed the researchers to dial in and find rare variants impacting intelligence.[ref]

Thus, as a simplification, about half of the genetic variants related to intelligence are common (found in more than 1% of the population), and the other half are rare (<1%).

We all have rare mutations in our DNA. Sometimes these mutations cause a big change, but most often, the mutations cause either no detectable change or affect some trait in a small way. It is interesting to see that some of these rare variants add to IQ.

Identified pathways:

Unsurprisingly, genes involved in neuronal function have been top hits in GWAS studies. Neurons in the brain use electrical impulses and chemical signals to transmit information. The neurons send signals to other neurons through chemical signals released in the synapse or area between neurons.

Examples of genes identified in GWAS studies on intelligence include:[ref]

  • SHANK3, which is involved in synapse formation in neurons
  • DCC – encodes a receptor involved in the way neuronal axons work
  • ZFHX3, a regulator of neuronal differentiation
  • BMPR2, which is active in embryonic formation

As one study puts it: “We found evidence that neurogenesis and myelination—as well as genes expressed in the synapse, and those involved in the regulation of the nervous system—may explain some of the biological differences in intelligence.”[ref]

Executive Function and Intelligence:

Genetic variants only minorly influence basic cognitive tasks. In other words, there isn’t a lot of genetic variation in everyone’s basic cognitive abilities. However, the higher-order functioning variation is explained by gene changes.

There is a strong overlap in genetic impacts on executive function and intelligence. Psychologists define executive function as the cognitive processes involved in planning, attention control, working memory, and problem solving. These functions originate mainly in the prefrontal cortex region of the brain.[ref]

Researchers have discovered a clear connection between executive function and the same genes that influence intelligence. Executive function is defined as “cognitive processes that coordinate, monitor, maintain, and manipulate more basic processes to give rise to higher-order reasoning, learning, and goal-directed behavior.”[ref]

Much of the genetic variation contributing to intelligence scores does not affect basic comprehension and rote memory. Instead, it is entwined with higher-level executive function genes.

Researchers testing executive function genes are looking at the ability to switch attention to different tasks, being able to delay gratification, working memory, and the ability to update new information.

Brain Volume and Intelligence

Are bigger brains smarter? Not always. However, a new genome-wide association study shows a partial overlap in variants related to intelligence and variants related to brain volume. The overlapping pathways are in the signaling pathways regulating cell growth.[ref]

Nature vs. Nurture: Other factors impacting intelligence

With the heritability of intelligence estimated to be about 60-70%, the remaining portion is environmental.

In the nature vs. nurture argument, there is undeniably an impact of early childhood home life. For example, a preschooler surrounded by loving care, books, quality food, and educational toys is going to thrive compared to one who is neglected or abused.

Let’s look at some of the less obvious impacts on childhood IQ…

Inflammation decreases children’s intelligence

A recent study in Southeast Asia discovered that elevated immune system markers were associated with lower general intelligence in children. The researchers did proteomics testing (checking a bunch of different nutrients, proteins, metabolites, and hormones in the plasma) and found that markers of subclinical inflammation were linked to lower developmental test performance.[ref] I like that the researchers went into this with a testing method that looked at such a wide range of markers. They did not simply assume they needed to look at specific vitamins but instead sampled the complete spectrum.

It makes sense that low-grade, chronic inflammation would affect kids’ cognitive function. Inflammation can cause cognitive dysfunction in adults – from brain fog to chemo brain to neurodegenerative diseases.

A study in Spanish children looked specifically at inflammatory markers. The results showed that higher TNF-alpha levels, an inflammatory cytokine, were associated with lower GPAs and lower math scores.[ref] Another study also linked higher TNF-alpha levels to obesity and lower math scores in school-aged children.[ref]

Nutrient deficiencies, toxin exposures, and Intelligence

Lead exposure during development decreases IQ in children. Genetic variants related to detoxification and inflammation play a role in how much exposure to heavy metals affects IQ.

Exposure in utero to organophosphates is also related to decreased IQ in kids. Organophosphates are commonly used as pesticides and are also found in flame-retardant chemicals.

A study found that the mother’s PON1 genotype made a difference in the decreased IQ levels of their offspring. PON1 is part of how organophosphates are detoxified in the body.[ref]

Ancient Humans and Intelligence

I’ve always just assumed people have gotten a lot smarter over the years… All of our advances are due to modern humans being just a whole lot smarter than our cave-dwelling ancestors. It turns out this isn’t true. (You know what they say about assuming…)

So how smart were our ancient ancestors?

With new sequencing and DNA extraction techniques, scientists have recently been able to sequence genomes from ancient skeletal remains. One study looked at 12,000 genetic variants in individuals from around 4,000 years ago (one from Japan and a family from Russia).

The results found that the IQ based on genetic variants should be very close to modern humans’ average IQ (~100).[ref]

Intelligence Genotype Report

Caveats: Your 23andMe, AncestryDNA, etc., data only covers a portion of your genome. Thus, this report only covers SNPs commonly found in direct-to-consumer testing — and leaves out quite a bit.

Use this as more of a ‘that’s interesting’ report – rather than really telling you anything about intelligence. Keep in mind that the genome-wide tests involve adults, so some of the results may not apply well to children.
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Making the most of your cognitive abilities.

This Lifehacks section is full of research-backed options for improving cognitive function. While there is no Limitless pill to make you super-intelligent, there are a bunch of ways to slightly improve cognitive function. Pick a few, experiment, and see what works for you.

Energy for the brain:

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Why join Genetic Lifehacks?

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~ You'll see your genetic data in the articles and reports.

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About the Author:
Debbie Moon is the founder of Genetic Lifehacks. Fascinated by the connections between genes, diet, and health, her goal is to help you understand how to apply genetics to your diet and lifestyle decisions. Debbie has a BS in engineering from Colorado School of Mines and an MSc in biological sciences from Clemson University. Debbie combines an engineering mindset with a biological systems approach to help you understand how genetic differences impact your optimal health.