How much of intelligence is genetic?

Whether it is genetics or environment that plays a role in determining intelligence has always remained an important question.

This is a controversial topic in the history of psychology, and to date, new studies have come up trying to understand the relationship between genetics, environment, and human Intelligence Quotient (IQ).

Many such studies conclude that a significant part of human intelligence is genetically influenced.

However, the same studies suggest that the environment may still play a role in molding the genetic trait. 

Genetic Influences on Intelligence/IQ

One of the earliest studies that attempted to understand genetic influences on IQ was the twin studies by professor Sir Cyril Burt. 

His studies, published between 1943 and 1966, concluded that genetics might significantly influence IQ levels. 

Other recent studies claim that the heritability of intelligence could be as high as 0.8 (on a scale of 0.0 to 1.0). 

Some of these studies examined the IQ scores of monozygotic (identical) twins and dizygotic (fraternal) twins. 

Monozygotic twins share 100% of their genetic material, while dizygotic twins may share an average of 50% of their genetic material.

These studies reported that the IQ scores of monozygotic twins are more similar than that of dizygotic twins. 

In a household with biological and adopted siblings, the IQ levels of biological siblings may be more similar to that of adopted siblings. 

This also points to the fact that genetics may play a more prominent role in influencing IQ levels. 

Learn more about how genes affect your personality and behavioral traits

Is There An Intelligence Gene?

There is no single gene that controls intelligence levels. Instead, a person’s intelligence may depend on interactions between multiple genes.

A UK-based study analyzed the DNA variants from more than 240,000 people and reported that up to 538 genes might be associated with intelligence. 

That is why intelligence is called a polygenic trait. 

Is Intelligence Inherited?/Heritability of IQ

Studies ascertain that 30-75% of variations in people’s IQ levels could be genetically driven.

However, environmental influences may help or prevent a person from achieving the genetic potential of IQ levels. 

Environmental Influences on Intelligence/IQ

Socioeconomic Status (SES)

Socioeconomic status refers to the family or individual’s access to economic resources like money and their position in society.

According to experts, poverty or lack of financial stability may prevent a child from reaching their full genetic potential of intelligence. 

A research paper analyzed the IQ levels of children from different SESs.

According to the results, children of the highest and lowest SES backgrounds were, on average, separated by 6 IQ points at the age of 2 years. 

Further, by the age of 16, the IQ gap had almost tripled.

Malnutrition

Lack of nutrition affects IQ levels, especially in the initial few years of a child’s life. According to a study, malnutrition between the ages of 1 and 5 may reduce IQ levels by up to 15 points. 

Cognitive Stimulation At Home

Cognitive stimulation includes a variety of experiences the child has at home. Here are some cognitive influences affecting IQ levels.

• Encouraging comments and feedback at home improve IQ levels as a child grows.
• Children who face reprimands and negative criticism at home seem to grow with lower IQ levels.
• Mother-child interactions and relationships affect IQ levels. Children who grow up with involved and healthy mothers may have higher IQ levels as they grow.

Education

A study states that educational duration and IQ levels could be closely related. 

According to it, intelligence increases by 1 to 5 IQ points for every additional year of education. 

Is Intelligence Genetic or Environmental: The Verdict

A significant part of a person’s intelligence is inherited by birth. 

30-75% of variations in IQ levels could be due to genes, and multiple genes play a role in determining the intelligence potential of the individual. 

However, environmental factors may influence how much of the genetic potential the person achieves during the lifetime. 

For instance, a child could be born with high intelligence. However, environmental factors like low SES, malnutrition, or lack of right education may affect the child’s IQ. 

For a person to have high IQ levels, genetics and the environment must be favorable. 

Summary

1. The question of whether intelligence is inherited or environmentally determined remains a puzzle to date.
2. Latest studies show that 30-75% of intelligence could be genetically influenced. 
3. More than 500 genes work together to determine the IQ levels of an individual. That is why intelligence is called a polygenic trait.
4. Environmental factors like socioeconomic status, nutritional levels, educational duration, and cognitive stimulation can help or prevent a person from achieving the genetic potential of IQ levels. 

References

• https://medlineplus.gov/genetics/understanding/traits/intelligence/
• https://www.mensa.org/iq/genes-and-environment
• https://en.wikipedia.org/wiki/Heritability_of_IQ
• https://www.verywellmind.com/what-factors-determine-intelligence-2795285
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5754247/
• https://www.familyeducation.com/is-intelligence-inherited-a-genetic-explanation
• https://www.scientificamerican.com/store/subscribe/scientific-american-magazine/
• https://www.weforum.org/agenda/2017/06/scientists-just-found-40-new-genes-that-affect-your-iq/
• https://www.nature.com/articles/s41562-017-0135.pdf?origin=ppub
• https://www.intelltheory.com/burtaffair.shtml