Psychology 101: Intro to Psychology

If the above player doesn't work, try this direct link.

Have you ever wondered if your intelligence is entirely due to genetics or if it's shaped by the environment surrounding you? In this lesson, you'll learn about the factors that affect and influence a person's intelligence.

Do we inherit intelligence from our parents? What are the origins of intelligence? Is there any truth to the claim that genes determine it, or is intelligence solely the result of environmental factors? Many studies suggest that intelligence is influenced by both genetic and environmental factors.

We do know that people who share genes tend to have similar mental capabilities. Identical twins have near-identical genetic codes, and they often score nearly the same on intelligence tests. Biological children and their parents, who are likewise genetically similar, are more likely to have similar IQs than adopted children and their parents.

Measurable physiological factors also support biological and possibly genetic influences that affect intelligence. For one thing, larger brain size is loosely correlated with greater intelligence. So are the brain's glucose metabolic rate, or the speed at which it makes energy, and the speed of brain waves. But none of these things are solely responsible for intelligence.

Still, research shows that we aren't born with a biologically predetermined amount of intelligence that remains fixed for our whole lives. Environmental influences have been shown to impact test results. Both fluid intelligence, or the ability to learn new ways of doing things, and crystallized intelligence, or the stockpile of knowledge we've accumulated throughout our whole lives, have been shown to change over time.

The environments in which we live influence our intelligence. Twins raised in the same environment have IQs that are more similar than twins raised in different homes. Other studies suggest that peer groups, the people you associate with, can impact intelligence. For these reasons, education generally tends to improve intelligence, but poverty seems to harm it.

It's hard to distinguish between the hereditary and environmental factors that affect intelligence. Family members who share similar genetic makeup usually share living environments, too. Twin studies that look at twins separated at birth are one of the few ways for us to understand the impact of genes versus environment on intelligence.

It's unclear which biological and environmental causes contribute to the gradual but persistent increase in intelligence test scores over the years. This increase is known as the Flynn effect, named for psychologist James Flynn, and the exact causes are still unknown. Some psychologists think that improved nutrition and medical care are responsible. But others think it's because of environmental causes, like better and more widespread education.

To summarize, intelligence is affected by both genetic and environmental factors; it's the result of both nature and nurture. Genetic predisposition and environmental influences are often difficult to fully separate. Despite genetic factors, intelligence can be increased or decreased by environmental circumstances.