Intelligence Inheritance

Through the ages parents have argued about their children’s intelligence – has it been inherited from the mother or the father?

In recent decades, some older studies have suggested that genes related to intelligence are passed down from the mother to the child, as women have two X chromosomes compare to men having one X chromosome.   Having two X chromosomes was regarded as potentially increasing the likelihood of children inheriting intelligence-related genes from the mother. 

A study conducted by the University of Cambridge in 1984 identified a significant relationship between maternal genes and the development of higher brain function in babies and children, with the scientific basis lying in the existence of so-called “imprinted genes”.

However, more recent genetic studies have indicated that intelligence is a complex trait with contributions from both parents.  Intelligence is influenced by both parents’ genes and linked to a wide variety of genes.

Earlier studies, which suggested that children’s intelligence is more closely related to that of the mother, probably didn’t allow for the effect that the mother, as the primary caregiver, has on their children’s environment during the period of critical brain development.  Smart mothers tend to raise smart children!

So where does inherited intelligence really come from?  And how do you determine intelligence?

What is intelligence?

Intelligence is a very challenging and complex field of study, partly because it can be defined and measured in different ways.  A simple definition of intelligence from the Oxford dictionary states, “the ability to acquire and apply knowledge and skills”, while the Brittanica dictionary defines human intelligence as “mental quality that consists of the abilities to learn from experience, adapt to new situations, understand and handle abstract concepts, and to use knowledge to manipulate one’s environment.”

Intelligence is a complex trait which includes various cognitive abilities, such as:

• Learning, which refers to the ability to acquire new knowledge, understanding, and skills.
• Problem-solving, which refers to the ability to use critical thinking and creativity in order to identify and resolve complex problems.
• Reasoning, which refers to the capacity to analyze information and draw logical conclusions, and to make informed decisions.
• Adaptability, which refers to the capacity to adjust to new situations, environments, and challenges.
• Memory, which refers to the ability to retain and recall information, experiences, and skills.

Intelligence is just one of the terms used to describe the differences in people’s thinking skills.  Other terminology refers to cognitive ability, cognitive performance, cognitive functioning, and mental ability.  IQ (intelligence quotient) is sometimes used, although it has a very specific meaning in the field of psychometrics, where it is used to quantify intelligence and is measured through cognitive tests.

Some scientists argue that there is no single quality of intelligence, but rather multiple forms of intelligence.  American cognitive psychologist, Howard Gardner, Research Professor of Cognition and Education at Harvard University, developed a series of eight inclusion criteria that based on scientific principles.  We all have these intelligences, but people’s profiles of these intelligences may differ, based on genetics and experience.

Intelligence is obviously a complex trait, but how much of it comes from the genes we inherited, or the environment we have been exposed to?

How much does genetics contribute to intelligence?

There is little doubt that there is a heritable component of intelligence.  Scientists say the idea of specific genes for intelligence is a fallacy, as there are many different genes whose function affect intelligence, each making a small contribution to a person’s intelligence.  Studies conducted in 2018 attained DNA samples of over 200 000 participants and found hundreds of genetic loci that are significantly associated with intelligence.  (A genetic locus (plural loci) refers to the specific physical location of a gene on a chromosome.  It is essentially the “address” of a gene on the DNA.)

The complex interplay of many genes working in concert shows that it is not remotely possible that the genes that affect intelligence are inherited from the mother only. 

Findings of studies of family pedigrees, studies of twins, and recent advances in molecular genetics indicate that between 40% and 80% of the variance in IQ is attributed to genetics, which highlights a significant hereditary component.

Identical twins, which develop from a single ovum (egg), (while fraternal twins develop from two separate ova), share the same genetic makeup and often show remarkably similar IQ levels, even when raised apart.   A 2024 study found that identical twins raised apart showed an increasing trend towards similar IQ’s as they aged.  The researchers noted that this could indicate that the environment plays a more prominent part in IQ for younger children, but genetics start to play a bigger role as the children grow up.

Studies have shown that IQ scores of identical twins are more strongly correlated and are mor similar than those of fraternal twins. 

Other research has also shown that the heritability of intelligence increases with age.  During infancy, genetic factors account for about 20% of variances in intelligence, but this figure can increase to as much as 80% in later adulthood.  These findings suggest that genetic factors start to play a more significant role in determining intelligence as people age.

Studies of adopted children show that their intellectual abilities were more closely related to those of their biological parents than to those of their adoptive parents.  Studies also found that siblings who were raised together in the same environment have more similar IQ’s than those of adopted children, raised in the same household.

How much does the environment contribute to intelligence?

Genetics provides a foundation for potential, but it is not the sole determinant of one’s intelligence, as environmental and individual experiences also shape cognitive development.  Genetics can be viewed as the blueprint or starting point of intelligence, while the environment can significantly influence the development of intelligence.   Stimulation from the environment during critical periods of cognitive development can either strengthen or hamper intellectual growth.   

The environment includes factors such as home environment, parenting, education and availability of learning resources, access to nutritious food, and healthcare.

The development of children’s intelligence is influenced by the environment in which they grow up, especially the socio-economic status of the family, which can affect the availability and quality of early educational interventions, such as educational resources, books, challenging problems, and intellectual discussions.  Stimulation in this regard is likely to aid the development of improved IQ scores, while encouragement and emotional support contribute to a learning environment and to promoting intellectual curiosity.

Studies have found that first-born children tend to have higher IQ’s than younger siblings.  It may be attributed to first-born children receiving more attention from their parents, but research also suggests that first-born children are expected to perform better on a variety of tasks, while younger siblings face less task-focused expectations from their parents.

Access to nutritious food is an important environmental factor, as malnutrition can severely deter brain development as well as cognitive function.

The educational environment plays a vital role in the development of intelligence, as a well-rounded and challenging education system not only provides information, but it challenges students to think critically, to understand abstract concepts, and to solve complex problems.  Including arts in the curriculum fosters creativity, which is an often-overlooked aspect of intelligence.  A robust education system enables students to reach the upper limits of their intellectual capabilities.

Environmental influences start from the womb, where maternal nutrition and health play a role, and continue throughout life.

Conclusion:

The age-old debate about where our intelligence comes from – nature or nurture – has resulted in a significant number of studies, especially in the field of genetics over the past two decades.  Although research is ongoing, the answer seems to be not nature or nurture, but both.

We are created and changed both by what we are (referring to our genes) and what we experience (referring to our environment).  Our every trait has a genetic component and an environmental component. 

While our genetics may provide our intellectual capacity, our environment determines whether we reach our full intellectual potential.  Both appear to be equally important.

References:

Is intelligence inherited from the mother or the father?  Published online during 2017.  TRT World.   Turkish Radio and Television Corporation.  Turkey.  (www.trtworld.com)

Is intelligence determined by genetics?  Published online and updated on 1 August 2023.  Medline Plus.  National Library of Medicine.  USA.  (www.medline.gov)

Exploring origins: Where does high IQ truly come from?  Published 14 February 2024.  Vanguard Gifted Academy.  School in Batavia, Illinois.  USA.  (www.vanguardgiftedacademy.org)

Genetic variation, brain, and intelligence differences.  Published 2 February 2021 in Molecular Psychiatry.   Nature.  (www.nature.com)

Intelligence and genetics.  Published online, 2024.  EBSCO.  (Provider of research databases.)  USA.  (www.ebsco.com)

Genetic and environmental influences on intelligence.  Published online and updated on 28 January 2024.  Verywellmind.  (www.verywellmind.com)

Theories of intelligence in psychology.  Published online and updated on 17 July 2024.  Verywellmind.  (www.verywellmind.com)

From father or mother: Science finally clarifies from whom children inherit intelligence.  Published online.  MSN.  USA.  (www.msn.com)

Gardner’s theory of multiple intelligences.  Published online and updated on 26 March 2025 in Simple Psychology.  Prof Howard Gardner is an American cognitive psychologist, and Research Professor of Cognition and Education at Harvard University.  USA.  (www.simplepsychology.org)

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