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Is Intelligence Genetic? - Genes' Influence on Intellectual Abilities

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  • 0:09 Intellectual Ability &…
  • 2:03 Studies
  • 3:09 Misconceptions
  • 4:45 Lesson Summary
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Lesson Transcript
Instructor: Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

What is the role of heritability in determining our intellectual abilities? Is intelligence genetic? Explore what part our genes play and find answers to these questions in the following lesson.

Intellectual Ability and Heritability

Many researchers have studied how our intellectual abilities are affected by genetics. Most believe that a large number of genes each play a small role in our intellectual abilities, but it is difficult to isolate and identify these genes.

Imagine you have a number of necklaces with 20,000-25,000 similar beads strung together. Now imagine you are looking for 3,000 specific beads on each necklace, but you're not sure what they look like or even if they will look the same on each necklace. This is a bit like trying to find the genes that influence our intellectual abilities.

Genetic research in this area can also be challenging because intellectual ability, or intelligence, is considered a complex trait. A complex trait is a trait that is influenced by many different genetic and environmental factors. Because intellectual ability is a complex trait, most researchers recognize that the genetic portion of our intelligence cannot be completely separated from the environmental influences we each experience. Even though researchers acknowledge the important role that environment plays, studies show a significant level of heritability in intellectual ability.

Heritability is the amount of variability that is genetic in origin. Heritability is measured with a value between 0 and 1. A heritability of 1 would indicate that all of the variation is genetic in origin. A heritability of 0 would indicate that none of the variation is genetic in origin. Depending on which research study you examine, intellectual ability has an estimated heritability between .4 and .8. Most researchers agree to a heritability for intellectual ability that is somewhere around .5. This means that evidence suggests our genetic makeup plays a significant role in intelligence.

Twin and Adoption Studies

Some of the most convincing evidence for a genetic component to intellectual ability is provided by twin studies. Researchers have performed many studies comparing the IQ of fraternal twins and the IQ of identical twins. Identical twins come from the same fertilized egg. Because of this, they share 100% of the same DNA. Fraternal twins share only 50% of the same DNA because they come from two separate fertilized eggs.

Identical twins were found to have IQ scores that were more similar than the IQ scores of fraternal twins. This was even true when the identical twins were raised in separate households. This discovery can reasonably be attributed to DNA. This means that we can assume that genetic influences account for the similar intellectual abilities of identical twins.

Researchers have also provided evidence for the heritability of intelligence through adoption studies. The IQ scores of adopted children have been found to be more closely related to their biological parents even though their environment matches that of their adoptive parents.

Misconceptions

There are some misconceptions about genetics and intellectual ability. For instance, a person might be led to believe that two parents with a higher IQ will produce children with equal or higher intelligence. This is not necessarily correct. The theory of regression towards the mean actually suggests that parents who are at the extreme high or low end of a trait will have children who are closer to the average for that trait.

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