Genetic and Environmental Influences of Schizophrenia: Causes and Effects

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  • 0:05 Schizophrenia
  • 1:38 Genetics
  • 3:20 Environment
  • 5:41 Lesson Summary
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Lesson Transcript
Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

For years, scientists have debated which has more influence on people: nature or nurture. In this lesson, we'll look at the genetic and environmental influences on the mental disorder schizophrenia.


What causes people to act the way they do? For years, scientists have debated over which plays a larger role in psychological and physical health: genetics or environment. This is often called the nature versus nurture debate. For example, Jimmy is really good at basketball. Partly, that's because he's tall, but he also has good skills, such as being able to jump and the ability to make a shot. But are his skills the result of his biology? Was he just born with greater-than-average talent for basketball?

Maybe. But consider this: What if, when he was very young, Jimmy was taller than the other kids. Because of that, many people told him that he should play basketball. He practiced a lot and played a lot. When he joined a little league basketball team, the coach gave him extra attention because he was taller, and therefore, assumed he was a better player.

Practice, extra attention from the coach, getting the chance to play… all of these are environmental factors that might make Jimmy a great basketball player. So, which is responsible for Jimmy's talent, genetics or environment? Or, is it a combination of the two? The mixture of nature and nurture goes beyond playing basketball.

Psychological disorders can also be traced back to a combination of genetics and environment. A good example of this is schizophrenia, a psychotic disorder that involves suffering from hallucinations and delusions, among other things. Let's look closer at the role genetics and environment play in schizophrenia.


For a long time, scientists have known that genetics play a role in determining whether or not you develop schizophrenia. Genetics are the biological markers, or genes, that parents pass down to their children. Think back to Jimmy: His genetics made him tall. There wasn't anything he could have done to make himself taller; his height was determined by the genes he got from his parents. Scientists know that schizophrenia is genetic, based on the prevalence of the disorder in the population.

About 1% of the general population has schizophrenia. But if you look at people with blood relatives who have schizophrenia, that number goes way up. For example, someone who has an identical twin with schizophrenia has a 40-65% chance of developing it themselves. And if both biological parents have schizophrenia, a person has almost a 50% chance of developing the disorder. Because those numbers are so much higher than the normal population, it is clear that genetics play some kind of role in schizophrenia.

But notice that having an identical twin with schizophrenia increases your chances of developing it to 40-65%. Identical twins have identical genes, so if it was purely genetics, then someone with a schizophrenic identical twin should have a 100% chance of developing schizophrenia.

Scientists have identified several different combinations of genes and gene mutations that might cause a person to be predisposed to schizophrenia. However, research is ongoing, and they do not know all of the genes that play a part in schizophrenia. They also don't know exactly how genes contribute to the disorder, or how to predict whether a person will develop schizophrenia based on their genes.


So, we know that genetics have something to do with the development of schizophrenia, but that it's not completely genetic. That's where the environmental causes of the disease come into play. There are three main types of environmental causes of schizophrenia: fetal issues, drug use and life experiences.

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