Is Intelligence Inherited? A Genetic Explanation

Do you ever wonder if your child's intelligence was inherited from their super smart parents or if their intelligence has more to do with environmental factors? 

Unsurprisingly, the answer is…both! Human intelligence is a fairly equal mix of genetics and environmental influences. 

Genetic differences in cognition and cognitive ability are more likely to be passed on from mother to child than from father to child (so for all the moms reading this, you were right all along). 

Related: Is Personality Genetic?

What is Intelligence?

An exact definition of intelligence is difficult to pin down, but generally, cognitive ability refers to the ability to learn from experiences and adapt to changing environments. Cognitive function includes reasoning, planning, and problem-solving skills, as well as the ability to think abstractly and understand complex ideas.

Intelligence differences are based on both genetic factors and environmental influences. Actual brain development is a combination of potential and the ability to reach that potential. Human intelligence depends on what a person is capable of achieving and what they actually do achieve.

How is Intelligence Measured?

Geneticists know that cognitive ability is influenced by both genetic factors and environmental factors. To draw such conclusions, they have had to base their studies on an agreed-upon definition of general intelligence.

So how do you measure general intelligence? It isn't easy when there are so many ways to be 'smart'. There are certainly rocket scientists who can't spell to save their lives and artistic virtuosos who can't balance a checkbook.

Most genetic research relies on the Intelligence Quotient (IQ test) to create a baseline for human intelligence studies. Researchers use IQ scores to compare intelligence differences and to ascertain whether and to what extent heritability plays a role.

It is important to note that IQ tests have many critics. Some people argue that traditional IQ tests measure what a person knows, rather than how they think. They also ignore or underestimate important contributions to intelligence, such as social skills, motivation, creativity, curiosity, or empathy (otherwise known as emotional intelligence). 

The Different Types of Intelligence 

In fact, the Theory of Multiple Intelligences claims that we have eight different types of human intelligence, with IQ only measuring two or three (logical-mathematical, linguistic, and possibly spatial). Great dancers and athletes score highly in bodily-kinesthetic; musicians have great musical intelligence and farmers are particularly talented in naturalistic intelligence. 

Another major flaw is the results of an IQ test are only a snapshot, a record of a moment in time that shows how a person performed on a particular test at a particular time. 

Also, consider this – your IQ score is not a fixed number – it can change. The structure and function of children’s brains develop as they grow, which can cause a change in IQ. 

IQ Tests Can Be Biased 

Socioeconomic factors like poverty, stress, and your diet also affect your IQ. In fact, recent studies have shown that children from a lower socioeconomic background adopted into wealthier families often see their IQ scores increase by 15 to 20 points.

One other important factor that some researchers have pointed out, is that IQ tests have “cultural specificity” – they are biased towards people who live in the society in which they were developed – namely white, western society (Ford, 2005). This means they might not give an accurate measurement of a person’s intelligence in culturally diverse settings.

With all these flaws, you might argue that we need to develop a more modern approach to intelligence testing. Robert Plomin, one of the leading behavioral geneticists of our time based at King’s College in London, believes that the future lies in studying our DNA to predict intelligence (Plomin & Stumm, 2018). This could mean that rather than take an IQ test, we would get our genome sequenced to take a closer look at how our genes influence our intelligence.

That begs the question…

Is There an Intelligence Gene?

The short answer is no, there is not a specific gene that determines overall cognitive function. Intelligence does have a genetic basis, but it is a complex trait, which means it is the result of complex interactions between a number of genes.

The heritability of intelligence only tell part of a person's story too. Although genetic variants do play a large role in whether a person has a high IQ, genetic studies show that general cognitive ability is also influenced by socioeconomic status and whether a person has been given the chance to achieve their potential.

Is Intelligence Inherited?

General intelligence definitely runs in the family. Twin studies (on both identical twins and fraternal twins) have found a heritability of IQ between 57% and 73%, and in some cases, even higher. This means that heritability plays a bigger role than the environment in creating IQ differences among individuals.

Interestingly, genetic studies have revealed that a child's IQ score is less affected by intelligence genes than an adult's. This could be because children are still developing their cognition and may be in different stages of brain development. The individual differences between the results in studies on children also indicate that studies on the genetics of intelligence should be based on those which look at teens and adults, rather than those that focus on children.

I Got It From My Mama

​Research shows that parents with higher intelligence generally have intelligent children. (Martinez et al, 2022) This is due partly to the inheritance of genes linked to intelligence but also parents with higher education are more likely to provide a cognitive-rich environment and tend to encourage their children to achieve more highly in education.

Genes controlling cognition are more likely inherited from the mother than from the father, according to studies in genomics. Many of the alleles containing intelligence determinants are carried on the X chromosome. Because women possess two copies of the X chromosome while men carry only one, it is more likely for these alleles to be passed on to the children.

In fact, it could be that general cognitive ability comes only from the mother. Some studies on the genetics of intelligence have found that genes for advanced cognitive functions which are inherited from the father may be automatically deactivated. These genetic determinants are called conditioned genes.

Moms can influence their children’s intelligence in more ways than just the genes they pass on. Research revealed that diet during pregnancy may influence a child’s neurodevelopment. (Freitas-Vilela et al, 2018) 

Scientists carrying out a study on pregnant women gave each group a different diet to follow throughout their pregnancy. Even taking into account differences in socioeconomic status, breastfeeding, and the child’s diet, they found the children of the women who followed a diet high in fruit and vegetables had a higher IQ at age 8.  

Race and Intelligence

Genetic research maintains that there is no correlation between race and general cognitive ability. This is supported by the fact that race is a social construct and not something that exists on the genome. In other words, we are all human. 

You do not inherit a specific race and your race has no bearing on how you perform on intelligence tests. Geneticists maintain that any past studies that claimed the opposite were flawed and did not take socioeconomic status, education inequality, and other environmental influences into consideration. 

Environmental Factors and Intelligence

Genetics plays a role in how a person performs on intelligence tests, but there are also environmental predictors and determinants – intelligence is influenced by both nature and nurture

Not getting a healthy diet (malnutrition) in the early part of life (1-5 years) results not only in a delay in physical growth but also a reduction in IQ by 15 points. Another major environmental factor on intelligence is the amount of cognitive stimulation a child receives at home.

 As a child grows up, the quality of education their receive seems to have quite a large role in determining IQ (Makharia et al., 2016). It is not only these social factors but physical ones too. Studies have shown that physical exercise can affect intelligence. In children, exercise has a role in creating and consolidating memory.

Does Birth Order Affect Intelligence?

If you are not the eldest of your siblings you probably don’t want to read this but studies have shown that first-born children tend to get the brains and have higher IQs than their later-born siblings (Lehmann et al, 2018).

Experts believe that this difference in level of intelligence does not have a genetic influence, but is due to environmental factors. There are multiple theories that explain why. 

First-borns tend to get more attention from their parents, as they typically spend their first few years as an only child, with parents who have time to focus on them alone. They also benefit from teaching their younger siblings, which helps them to build their learning skills.

Reaching Genetic Potential

Socioeconomic status plays a major role in what opportunities are afforded to a person during their life. Chances to develop one’s intellect are necessary to reach one’s full genetic potential.

Think of it this way: A person born with the genetic predisposition for average intelligence might reach an average IQ score if they grow up with a healthy diet and a well-rounded education. 

If they have a parent at home to help make sure they get their homework done, the family can afford healthy meals, and the neighborhood offers the chance to get outside and run around, they're more likely to perform at the maximum cognitive ability genetically afforded to them. 

But, if they don't have these support systems in place, (and these are just a few examples among many), they may reach a lower IQ score than this with the same genetic determinants.

Another way to understand how environmental influences correlate with genetic predictors is to think of an athlete. Inherited traits such as strength, agility, and height clearly influence an athlete's highest potential. 

But if he never learns to play basketball or doesn't have access to the best coaches, he may not be able to reach this potential. On the other hand, a child who has all the best athletic support but just isn't genetically predisposed to success in a certain sport can only go so far.

When it comes to mental ability, environmental factors have the highest influence during childhood. That's why it's so important to promote equity for children.