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- [Voiceover] Let's say that this is you and that these are your friends. What kind of things are you most likely to have in common with these friends? Well, it turns out just about everything, and that's because similarity or how similar someone is to us is a huge predictor of attraction. Compared to any two random people that you might find, close friends and couples are far more likely to share common attitudes, beliefs, and interests, and it doesn't stop there. We tend to befriend and partner up with people who match our age and race and religion, even things like economic status and educational level. We like people who are like ourselves, and this has been demonstrated through a number of surveys and correlational studies, but it's also been demonstrated experimentally as well. In one study, university students were brought into a lab, and they were told that they were going to be playing a game with another student. In reality, the other student was a confederate, meaning that they were in on the study the whole time. Participants were split into one of two conditions. In one condition, they were shown the image of the other player, in this case our confederate. In the second condition, participants also saw a picture of the other player, but unbeknownst to them, that picture had some of their own facial features mapped onto it, and the results of this study showed that the individual was much more likely to cooperate with the other player and to deem them as trustworthy when the picture of the other player had some of their own facial features morphed into it. Other studies have shown similar findings. We're more likely to think that another individual is attractive when their facial features are morphed with our own. We're even more likely to vote for political candidates whose photographs have been changed to include some of our facial features. So, when I say that we like people who are like us, I don't just mean that in terms of attitudes and interests. We are more likely to like people who are similar to us on any level, even if they just share some of our facial features. So, we've noted that similarity can help to bring people together, but does it help them stay together? Do friendships and relationships tend to last longer the more similar we are? And the research has shown that the answer is yes, but it's a little bit complicated, because I think it would be really easy to say that couples who are really similar to each other share a lot of attitudes and share a lot of interests. And it seems fairly obvious how those shared interests could keep two people together over long periods of time, but it could also be the case that couples stay together because of perceptions of similarity. and this could mean one of two things. The first is that as couples stay together and share their interests with each other, their interests tend to become more aligned over time. So, it's not that couples who stay together for a long time are similar in general. More like they become similar as time goes on. Another option would be that perceived similarity could be just that, perceived. Maybe individuals who stay together for long periods of time merely think that the other person is similar to them. After all, the way that this data is collected is typically through surveys. So, it could be that couples who stay together for long periods of time aren't actually that similar at all, they just think that they are. The thing I find to be most interesting about the similarity effect is what it might leave out. Because it's not really hard to see how the similarity effect could actually become a similarity bias, because while on the one hand it predicts that we will like people who are like us, it also kind of implies that we will not befriend people who are different from us. So, the same force that helps pull people together, might cause them to exclude individuals who are physically or culturally different from themselves.