Similarities Attract

Podcast

Similarities Attract

Transcript

Seeking our genetic soulmates. I’m Bob Hirshon and this is Science Update.

We've all heard that "opposites attract," but in reality, it’s similar people who tend to stick together. That’s according to psychologist J. Phillipe Rushton of the University of Western Ontario in Canada.

He and his colleague found that when it comes to personality and beliefs, people in their study were about as similar to their own spouses and best friends as they were to a fraternal twin. Spouses matched each other more closely on personality traits that were more heritable.

Rushton:
… implying that it is genetic similarity that people are choosing, rather than similarity based on cultural upbringing.

Rushton says we may be biologically driven to seek mates who are just different enough to mix up the gene pool, but similar enough to pass plenty of our own genes to the next generation. I’m Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

This study is cleverly designed, and illustrates the many steps a scientist must often take to answer what looks like a simple question.

In this case, the question is: How similar are people’s personalities to those of their own spouses or close friends, and why? So first, the researchers had to find out just how similar people were. But while this question seems easy to answer on an everyday level (“Zack and Jen are a lot alike”), it’s hard to measure scientifically. What exactly do you measure, anyway? How do you measure it?

In this case, the researchers used a detailed questionnaire about personality and beliefs as their yardstick. They asked sets of twins – some identical, some fraternal – to fill them out, and also asked the twins’ spouses and best friends to do the same. Not surprisingly, they found that identical twins were more similar to each other than to anybody else. Identical twins share the exact same DNA, and it’s well known that they not only look alike, but also have similar personality traits, and even share similar preferences in food, clothes, music, hobbies, and so forth.

But when the researchers looked at pairs of spouses and best friends, they found that they were about as similar to each other as pairs of fraternal twins. Again, it’s not surprising that fraternal twins would be similar: they share half their DNA, like any pair of ordinary siblings, and they’re also usually raised in the same home, attend the same schools, and so forth. But spouses and best friends aren’t related at all, and might come from many different backgrounds. So why are they so similar?

One possible answer is that we choose people who are like ourselves based on environmental factors, like culture, family, education, or religion. In other words, we’re taught, through our upbringing, who to make friends with and who to marry. While this may be true to some extent, the study suggests that there’s more to it than that.

Here’s why: It turns out that some aspects of our personality are more heritable – in other words, influenced by our genes – than others. It’s not necessarily what you would expect, either: for example, enjoying reading is more heritable than wanting to travel the world alone.

Looking at the people in their study, they found that the more heritable a personality trait is, the more likely that a husband and wife (or pair of best friends) would share it. That suggests that we seek out our partners based more on genetically determined personality traits than environmentally determined personality traits. But how is this possible, when we ourselves don’t know – at least consciously – which traits are more genetically influenced and which are less so? And what is the advantage of this?

The answers to these questions remain uncertain. Dr. Rushton believes it may relate to kin selection in other animals. Most animals can recognize their own family members and are more likely to help them, or sacrifice for them, than for unrelated animals. One possible explanation is that by helping relatives with similar genes, one’s own genes are more likely to survive to the next generation. Perhaps that’s why we choose people who are genetically like ourselves to protect, defend, and have families with.

Now try and answer these questions:

1. What questions did this study seek to answer?
   
2. What does it mean to say that one personality trait is more heritable than another?
   
3. Why did the researchers conclude that our genes influence our choice of spouse?
   
4. Suppose that identical twins were exactly as similar to each other as they were to their own spouses. What conclusions would you draw?

Going Further

The Science Netlinks lesson Finger Length discusses a study that found clues to personality in a person’s fingers.

Read more about kin selection in the National Geographic News article Biologists Study Evolution of Animal Cooperation.

Beauty, an article by Australia Broacasting Company's Dr. Karl and featured on ABC's Science Online, delves into the relationship between body symmetry and attractiveness.