Twin and Adoption Studies: Practices & Findings

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  • 0:02 Genetic Research
  • 0:45 Nature vs Nurture
  • 2:16 Adoption Studies
  • 4:19 Twin Studies
  • 6:07 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.

What is more influential, nature or nurture? How can scientists know for sure? In this lesson, we'll look at studies designed to separate the effects of genetics and environment on people's behavior, twin and adoption studies.

Genetic Research

Eric is interested in why people become addicted to drugs and alcohol. He's heard that a lot of times, children of addicts become addicts themselves. So does that mean that it's something that's inherited, like brown hair or freckles?

Eric is interested in the impact of genetics, or inherited traits, on people's behavior. This is something that psychological research often tries to answer. But it's a very complicated question and one that Eric won't find an easy answer to!

Let's look at why genetic research is complicated and two types of studies that attempt to figure out how genetics influence our behavior, twin studies and adoption studies.

Nature vs. Nurture

So Eric wants to figure out why people become addicts. He knows that children of addicts often become addicts themselves, so he thinks that it could be genetic, like the color of someone's eyes or how tall they will become. In order to show that a person's genes are what make them an addict, Eric figures that he should just find a bunch of addicts whose parents are also addicts. After all, if a parent has red hair and their child has red hair, then we say that red hair is genetic. It should work the same way with addiction, right?

Not so fast! Unlike red hair, addiction can be influenced by many different things. Let's imagine that Eric studies an alcoholic and discovers that her father was also an alcoholic. Does that mean that she inherited a gene that made her an alcoholic? Or did she become an alcoholic because she was raised in an environment where alcoholism was normal?

These questions tap into a debate in psychology. Sometimes referred to as nature versus nurture, this debate tries to figure out whether behavior is more influenced by genetics or environment. A person's nature is their genetic makeup, while their nurture is their environment, or how they are nurtured within that environment.

As with Eric's subject, the answer isn't always easy to figure out. In reality, both nature and nurture influence our behavior. But the question is how much influence do each of them have on us?

Adoption Studies

Eric really wants to figure out what's going on with addiction and genetics. Is addiction all a product of a person's environment? Is it all genetic? Or, like most things, is it a combination?

As we've seen, studying nature and nurture can be complicated. There's no way for Eric to know if his subject is an alcoholic because she inherited the genes for it, or because she was raised in an alcoholic household, or if it's a combination of the two.

There are a couple of ways that Eric can study the effects that nature and nurture have on a person. One popular type of study is an adoption study, which compares an adopted person's behaviors to those of their biological parents and their adoptive parents.

Let's go back to Eric's subject. Her father was an alcoholic, and now she is, too. There's no way for Eric to know if that's due to her nature or her nurture. But imagine for a moment if the subject had been adopted when she was a baby and raised by parents who didn't drink alcohol at all. If she became an alcoholic as an adult, Eric might conclude that there's some sort of genetic influence on alcoholism.

Why would he guess that? In an adoption study, if a person is more like their biological parents, the likelihood of there being a genetic component is high. Their genes, which they share in common with their parents, are helping to shape their behavior. On the other hand, if a person in an adoption study ends up more like their adoptive parents, the environment is probably shaping their behavior more. After all, the environment is what they share with their adoptive parents, not genes.

So, if Eric's subject is adopted as a baby and ends up in a family of teetotalers, and the subject grows up not to be an alcoholic, then Eric might believe that alcoholism is mostly due to the environment, not genes. But if she ends up an alcoholic even though she's raised by people who don't drink, then he might conclude that her genes are influencing her behavior.

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