The Effects of Heredity on Intellectual Development

Updated November 21, 2016

There has long been a debate over nature versus nurture and which is more important when it comes to influencing a child's intellect as well as his overall behaviour. Many researchers believe that both heredity and environment play an important role in determining a child's intelligence, but nature may play the more important role.


Heredity refers to the nature or the genetic make-up that a person consists of from the moment he is conceived until death. Nurture means the environmental and external factors that a person is exposed to, which include social and physical environments.

Twin Studies

Studies show when identical twins are separated at birth and live with different families and in different environments their IQs nevertheless remain quite similar, which indicates that heredity has a strong bearing on a person's intelligence. Usually identical twins have an even more similar IQ than fraternal twins because identical twins are genetically equivalent having come from the same fertilised egg that divided into two. Fraternal twins come from two separately fertilised eggs.

IQ Relationship to Biological Parents

According to, adoptive children tend to have an IQ that more closely correlates to their biological parents' IQs than their adoptive parents'. In fact, the correlation between children who are adopted and their biological parents' IQs become stronger as they age and the correlation between these children and their adoptive parents' IQ becomes weaker in late adolescence. This strongly points to the influence of genetics and heredity.

Biological and Adopted Children

When a couple has biological children and then adopts a child, studies have proven there is no significant relationship between the IQ of the biological children and the IQ of the adopted child, although they have been raised by the same parents in the same environment, which lends support to the hereditary argument.

Social Experiences

A child's social experience, however, has a more important role in brain development than scientists used to believe, and this role includes the formation of a child's intellectual capabilities. Environment, or the "nurture" part, of the equation is therefore very important in intellectual development.

Before Birth

Paul Thompson of the UCLA Department of Neurology explains that the way a brain is wired is decided before birth and this determines brain signalling speed and intelligence. However, nutrition, exercise, diet and nutrition also impact the brain and a person's intellect.

Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Cindi Pearce is a graduate of Ohio University, where she received her bachelor’s degree in journalism. She completed both the undergraduate and graduate courses offered by the Institute of Children’s Literature. Pearce has been writing professionally for over 30 years.