Chapter 4. How Would You Know If Personality Runs in Our Genes?

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C. Nathan DeWall, University of Kentucky

David G. Myers, Hope College

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Note: You will be guided through the Intro, Design, Measure, Interpret, Conclusion, and Quiz sections of this activity. You can see your progress highlighted in the non-clickable, navigational list at right.

Watch this video from your author, Nathan DeWall, for a helpful, very brief overview of the activity.

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So, how would you know if personality runs in our genes? To study this question effectively in your role as researcher, you need to DESIGN an appropriate study that will lead to meaningful results, MEASURE your participants’ personality traits, and INTERPRET the larger meaning of your results—considering how your findings would apply to the population as a whole.

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Twin Studies:

Experiments:

Case Studies:

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You have chosen Experimental design, which means you need to set up an experimental group and a control group. For example, when testing whether resisting tempting food causes mental fatigue, researchers have had participants in an experimental group resist eating a delicious food. They compared their levels of mental fatigue with those in the control group, who did not have to resist the delicious food. This allowed researchers to determine if exercising self-control by resisting temptation depletes people of their mental energy. (It does!)

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This is kind of difficult, isn’t it? To use an Experimental design, we would need to have an experimental group of people assigned to have high genetic similarity, and a control group of people assigned to have low genetic similarity. But you cannot make such assignments—you can’t assign people to have high or low genetic similarity. It is not biologically feasible!

For more on Research Ethics, click on “Video Hint” below.

So, EXPERIMENTAL IS NOT THE BEST RESEARCH DESIGN for this study. We’d get more helpful results by studying large groups of people who have naturally-occurring high or low levels of genetic similarity.

Click “Next” to go back and try again to select the most effective research design.

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Research Ethics:

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You have chosen Case Study as your design. With a Case Study design, you will choose one person or a small group of people, such as identical twins, who share a fetal environment and are genetically identical, or fraternal twins, who share a fetal environment but are genetically no more similar than ordinary brothers and sisters.

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What could we learn from these participant choices?

A small group of people who are identical twins You would need to compare identical twins with siblings who are not genetically identical. This way, you could compare the degree of personality similarity and determine if it changes with degree of genetic similarity. You would also want to study a large group (not a small group) in order to be able to apply your findings to the broader population.

A small group of people who are fraternal twins You would need to compare genetically similar fraternal twins with siblings who are genetically identical. This way, you could compare the degree of personality similarity and determine if it changes with degree of genetic similarity. You would also want to study a large group (not a small group) in order to be able to apply your findings to the broader population.

A small group of people who are identical twins and are extremely talkative, and another small group of siblings who are identical twins and are extremely withdraw Comparing personality traits in identical twins would not give you the information you need to determine if personality runs in our genes. You would need to compare talkativeness between identical twins and siblings who do not have identical genetic material. You would also want to study a large group (not a small group) in order to be able to apply your findings to the broader population.

A small group of people who are identical twins and another small group of people who are fraternal twins You are right that we would need to compare personality traits between identical twins and fraternal twins. However, you need to study a large group, not a small group of people (as you would in this case study approach), in order to be able to apply your findings to a larger population.

Trying to choose a sample of participants helps us realize that the CASE STUDY IS NOT THE BEST RESEARCH DESIGN to test this question. We’d get more helpful results by studying large groups of identical and fraternal twins, which would allow us to apply our results to the broader population.

Click “Next” to go back and try again to select the most effective research design.

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Nice work! You have correctly chosen to use a Twin Study design to test your research question.

Next, you need to choose the most appropriate participants for your study.

As the name suggests, with a Twin Study design, you will be working with groups of twins. Remember that identical twins share a fetal environment and are genetically identical, and fraternal twins share a fetal environment but are genetically no more similar than ordinary brothers and sisters.

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You chose A group of siblings who are identical twins, but this is NOT THE BEST CHOICE. It would be better to compare identical twins with same-aged siblings who do not have identical genetic material (fraternal twins). This way you could compare the degree of personality similarity in siblings who are genetically identical with those who are only genetically similar.

Click “Next” to try again to choose the most appropriate study participants.

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You chose A group of siblings who are fraternal twins, but this is NOT THE BEST CHOICE. You need to compare fraternal twins with same-aged siblings who have identical genetic material (identical twins). This way, you could compare the degree of personality similarity in siblings who are only genetically similar with those who are genetically identical.

Click “Next” to try again to choose the most appropriate study participants.

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You chose A group of siblings who are identical twins and are extremely talkative, and another group of siblings who are identical twins and are extremely withdrawn, but this is NOT THE BEST CHOICE. Knowing whether people are talkative or withdrawn does not give you the information you need to know whether personality runs in our genes. You would need to compare talkativeness between identical twins and same-aged siblings who do not have identical genetic material (fraternal twins).

Click “Next” to try again to choose the most appropriate study participants.

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Good job! You have correctly chosen to use a Twin Study design with A group of siblings who are identical twins and a group of siblings who are fraternal twins. Now you need to determine how best to MEASURE the relevant behavior or mental process, which in this case is personality—an individual’s characteristic pattern of thinking, feeling, and acting.

People have many personality traits. In your study, we will focus on how to measure two popular personality traits. The first trait is extraversion, or how much someone is sociable, fun-loving, and affectionate. The second trait is agreeableness, which refers to how much someone is soft-hearted, trusting, and helpful.

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You chose (1) Talkative (2) Like going to parties but always argue with others, but that is NOT CORRECT.

This option would tell you whether participants are extraverted (Talkative), but the second part of this option does not focus only on the trait of agreeableness, as it should. It asks participants again about their extraversion (“Like to go to parties”) and also asks about their agreeableness (“always argue with others”), which could confuse your participants’ responses.

Click “Next” to try again to select the best way to measure whether the personality traits extraversion and agreeableness run in our genes.

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You chose (1) Like spending time at zoos (2) Calm, but that is NOT CORRECT.

This option would not give you information about participants’ levels of extraversion or agreeableness. If you want to know whether the personality traits extraversion and agreeableness run in our genes, you need to measure relevant thoughts, feelings, and actions.

Click “Next” to try again to select the best way to measure whether the personality traits extraversion and agreeableness run in our genes.

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You chose (1) Interested in hiking dangerous mountains (2) My parents prefer routines, but that is NOT CORRECT.

Knowing whether participants are interested in hiking dangerous mountains does not give you information related to extraversion or agreeableness. Preferring routines also does not relate to extraversion or agreeableness. And you need to measure your participants’ personality traits, not how they perceive their parents’ personality traits.

Click “Next” to try again to select the best way to measure whether the personality traits extraversion and agreeableness run in our genes.

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Good job! You have correctly chosen to use a Twin Study design, in which you will compare personality scores between siblings who have different levels of genetic similarity. You also chose an appropriate sample of participants—a group of siblings who are identical twins and a group of siblings who are fraternal twins. You chose the following, appropriate questionnaire items for MEASURING two key personality traits—extraversion and agreeableness:

In similar studies, researchers have tested the hypothesis that the personality traits extraversion and agreeableness run in our genes. They have used twin studies like yours to estimate the heritability of these traits—or the extent to which variation among individuals can be attributed to their differing genes. Across numerous studies, extraversion and agreeableness do in fact show a genetic effect. That is, identical twins have more similar scores than fraternal twins do (Bouchard, 2004). So, we have an initial answer to our question. And the answer is Yes, personality does run in our genes.

Knowing this, you need to consider how you can apply what you’ve learned to the larger population—beyond the people you’ve studied. Consider where you might encounter roadblocks to confidence in your results. What factors might keep you from being able to apply what you’ve learned in a broader context?

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You tested whether the personality traits extraversion and agreeableness run in our genes. There are many factors that could affect personality. Nature is important, but doesn’t nurture matter, too? Factors that could interfere with our INTERPRETATION of results are called confounding variables.

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Confounding Variables:

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The confounding variables for your study would include those highlighted below:

The highlighted confounding variables would affect your confidence in your study design and measurement approach. You need to keep track of whether participants had parents who taught them to be talkative and agreeable to make sure your results are due to genetic differences between identical and fraternal twins and not what they learned growing up. You would also need to know whether participants grew up in the same environment or were separated at birth. This way you could determine what influence, if any, a shared environment might have on extraversion and agreeableness.

Neither clothing tastes nor impulsiveness relate to the personality traits you measured, and whether participants enjoy being an identical or fraternal twin also should not affect your study.

Unless you keep track of the highlighted confounding variables, you might draw incorrect conclusions about your study results.

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You may do better on the Quiz if you take notes while watching this video. Feel free to pause the video or re-watch it as often as you like.

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