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Key points
- Many couples look similar to one another.
- Reasons for this phenomenon may include in-group bias, implicit egotism, the familiarity effect, and sexual imprinting.
- However, there are individual differences in attraction to self-resembling partners.
- What's more, couples can grow to resemble each other over time through empathic mimicry or similarities in lifestyle.
Most of us have marveled at the uncanny resemblance between a couple. While sometimes famous couples look alike (e.g., Tom Brady and Gisele Bündchen, or Vincent Kartheiser and Alexis Bledel), many times the couples in question are friends, acquaintances, or random strangers. This phenomenon has gained so much attention that people now play “Siblings or Dating” games on various social media channels including Instagram, Reddit, and YouTube.
But why is it that people tend to date those who look like themselves? Some explanations are obvious, but others are lesser-known. Below are 9 reasons that couples can sometimes look like siblings:
1. Ingroup biases. One of the most obvious reasons that couples look similar is ingroup biases, such as same-race preferences in dating. Same-race preferences in dating are motivated by a variety of factors, research has found, including social network approval, perceptions of similarity, and perceived physical attractiveness.
In the U.S., ingroup biases in dating are found among many racial groups, including Whites, Black, Latinxs, and Asians, but to different extents. In a study of heterosexual college students, all four groups gave same-race members of the other sex higher attractiveness ratings than did outgroup members, but Latinx and Asian Americans rated Whites of the other sex as more attractive.
Among same-sex daters, White men as well as White, Black, and Latinx women have a strong tendency to prefer dating only their own race. Despite their relatively diverse upbringing, biracial individuals also show same-race preferences in partners.
2. Implicit egotism. While same-race preferences significantly narrow the dating pool and increase the likelihood that a partner will have similar features, they are clearly not enough to explain why many couples look like close relatives. After all, there is considerable diversity in appearance within racial groups.
Amusingly, studies have found that people are actually attracted to morphs of their own faces. In an experiment, researchers blended the faces of heterosexual participants with the face of their partners to create a "self-based morph." They also blended the faces of participants’ partners with a same-sex "prototype" to create a "partner-based morph." Although others rated the partner-based morph as more attractive, participants rated their self-based morph as more attractive than the partner-based morph.
The morph that was the most attractive to participants contained 22 percent of their own faces. Importantly, this preference did not operate at a conscious level—participants did not recognize their own faces in the image.
Another study also found that attraction to self-based morphs operates at an unconscious level. Again, participants found self-based morphs more sexually attractive. However, in a subsequent experiment, researchers informed participants in the experimental condition that “We are interested in studying incest. We want to know how attractive people find faces that are designed to resemble genetic relatives such as parents, brothers, and sisters” (p. 1207-1208). Participants who received this prompt rated self-based morphs as less sexually attractive, indicating that this phenomenon operates at an implicit level—individuals are not knowingly attracted to people who look like themselves.
3. Familiarity effect. People may prefer those who look like them due to the familiarity effect, or the tendency to like familiar stimuli. When we are exposed to a particular stimulus over and over, we will tend to like it more due to ease of processing. To our brains, easy means pleasant.
A study tested the role of the familiarity effect in the perceived attractiveness of faces. In support of the familiarity effect, researchers found that more distinctive faces were rated as less attractive and more familiar faces were rated as more attractive. Furthermore, increased exposure to faces led to higher ratings of attractiveness for both distinctive and familiar faces.
4. Game theory. Recall the famous scene in "The Beautiful Mind" during which mathematician John Nash (played by Russell Crowe) applies game theory to dating. John Nash and his friends all found the same blonde woman to be the most beautiful. However, Nash came to the conclusion that no one would “win” if they all went for her, so they must each go for her brunette friends instead.
Real life doesn’t work quite the same way, but perhaps “equilibrium” or an optimal outcome for all parties can be reached through another method. Researchers sought to examine two forces of human mate selection—selection of “good genes” (e.g., preference for the best) and “self-seeking like” (e.g., preference for self-resemblance).
Through a randomly selected sample of 36 couples, they found evidence of both forces. First of all, more attractive men and women were more likely to be together. Second of all, couples resembled each other in facial features. Therefore, people may achieve the best of both worlds by going for someone who looks like them, as self-morphs are uniquely attractive.
5. Sexual imprinting. In addition to preferring one’s own face, people may be unknowingly seeking the face of their parent. Researchers suggest that young children may learn what a desirable partner should look like through a process called sexual imprinting—that is, parents may model for their children what their future partner should look like.
To test this idea, researchers subliminally primed heterosexual men and women with a photo of their other-sex parent. Then they showed participants photographs of other-sex faces. In support of sexual imprinting, participants who were primed with an image of their own parent (vs. someone else’s parent) rated other-sex faces as more sexually attractive.
6. Emotional closeness with parents. Importantly, not everyone prefers partners who look like themselves or their parents. Studies have found individual differences in these preferences.
Researchers exposed heterosexual women to self-resembling male and female faces. Women who reported greater emotional closeness with their fathers were more likely to prefer self-resembling male faces (but not female faces). Self-reported emotional closeness with mothers did not influence preferences for self-resembling male or female faces. Earlier studies had found the same effects on women’s preferences for partners who look like their fathers. So although effects among men still need more investigation, individuals who are close to their parents may be prone to sexual imprinting (with the parent as the model) when it comes to their partners’ looks.
7. Similar social judgments. There may be more than what meets the eye when it comes to attraction to physically similar partners. Researchers found that the perceived personality of faces predicted both facial resemblance and the likelihood that a pair was an actual couple. The researchers suggest that couples may be similar in personality as a result of social cognitive judgments by others. In other words, people may pair with those who look like them because they have similar personalities due to others’ judgment of them. For instance, a person may grow to confirm others’ expectations of them (due to their looks) through the self-fulfilling prophecy.
8. Matching body type. While many studies have focused on facial similarities between couples, body type is another important factor in resemblance. Studies have in fact found that spouses are similar in their body mass index, weight, and height. This resemblance in body type may result from preferences for those who are similar or from shared lifestyles (in the case of weight).
9. Empathic mimicry. Sometimes couples don’t really look like each other—until later in life. Researchers collected images of spouses as newlyweds and 25 years later. They found that spouses became more similar in looks over time, and that this increase in similarity predicted greater relationship quality.
They proposed that spouses (especially those who are close to each other) may converge in facial features through empathic mimicry. That is, through empathy for one another, couples may feel similar emotions and make similar facial expressions, leading to similar facial musculature (and wrinkles/aging patterns) over a long period of time together.
Overall, although people make light of the phenomenon, the finding that couples look alike is robust and reflective of complex psychological processes. Pairing up with someone with similar physical features might be a way to be with someone uniquely attractive to us—as long as we don't realize it, that is.
Yet research suggests that there is more than what meets the eye. Couples who look similar may also be similar in their personality, lifestyle, emotions, and facial expressions—and they may be happier together, too.
Facebook image: Aleksey Boyko/Shutterstock
