Birds of a Feather: How Shared Traits Shape Friendships and Romance

When it comes to forming friendships and romantic relationships in the real world, the old saying “birds of a feather flock together” tends to hold true. Decades of social science research show that people are more likely to bond with others who are similar to themselves on a variety of observable traits . In fact, similarity – not “opposites attract” – is the norm in existing relationships, with complementarity being a rare exception . Below, we’ll explore five key types of shared traits – beliefs, behavioral traits (like personality and habits), skills/interests, physical attributes, and intellectual traits – and what the latest peer-reviewed research says about how each influences the formation and strength of offline friendships and romantic relationships. We’ll also compare which similarities matter the most for sparking new connections and for keeping relationships going strong over time.

Shared Beliefs and Values

What counts as shared beliefs? This category includes core values, religious faith, political ideology, morals, and attitudes about the world. These are the deeply held beliefs that shape a person’s worldview – for example, sharing the same religion, having aligned political views, or holding similar values about family, work, or ethics.

Impact on friendship: Shared beliefs provide a powerful foundation for friendship. People tend to gravitate toward others who validate their own worldview. Sociologists have long observed homophily – the tendency to associate with similar others – in social networks. We usually interact with people who match us demographically and ideologically, including religion and politics . For instance, one analysis of American social networks found that people’s circles are predominantly composed of others with similar religious affiliations and levels of religiosity . In other words, friends often share a faith or general value system. Shared values can create an instant sense of understanding and trust. If you meet someone who cares about the same causes or has the same religious upbringing, conversations flow more easily and the friendship may feel “meant to be.” On the flip side, large belief mismatches can be a barrier – differences in core values can lead to friction or simply less common ground to build a friendship on.

Impact on romantic relationships: Of all trait domains, similarity in beliefs and values appears to be one of the strongest factors in partner selection and long-term compatibility. Couples very frequently align on religion and politics. A large study of thousands of married couples in the U.S. found that political attitudes were among the most strongly shared traits between spouses – even more than personality or looks . In fact, the researchers concluded that people put more emphasis on finding a mate who is a kindred spirit in terms of politics, religion, and social values than on more surface traits like physique or personality . This sorting is reflected in statistics: For example, one 2024 analysis of over 4,000 Americans reported that nearly 77% of couples had the same party affiliation (only 23% differed), and fewer than 8% of couples were one Democrat and one Republican . Clearly, most people end up with partners who share their general political leanings. Those who don’t may face some challenges – the same study found that couples with differing political views reported slightly lower relationship quality on average . However, the researchers noted that factors like overall empathy and shared values in other domains can buffer the negatives of political discord . Shared religious belief is another big one: couples who practice the same faith often enjoy higher relationship satisfaction. A multi-nation study found that highly religious couples (who share active faith) had higher marital quality and even more fulfilling sex lives than mixed-faith or secular couples . By contrast, studies have linked large religious differences to lower marital satisfaction and well-being . The likely reason is that sharing beliefs – whether it’s a life philosophy, faith, or political values – gives partners a common framework for making decisions and understanding each other. It reduces fundamental conflicts about what’s “right” or important in life.

Comparing friendships vs. romance: Shared beliefs strongly foster both close friendships and romantic bonds. However, the stakes are higher in romance: A mismatch in religion or values might be a dealbreaker for marriage (think about disagreements on how to raise children or moral principles), whereas friends sometimes “agree to disagree” on politics or religion more easily if other bonds (like a shared hobby or history) compensate. Still, many friendships dofalter over clashing belief systems, especially in polarized environments. Overall, alignment in core beliefs is often cited as a top ingredient for deep connection in both platonic and romantic relationships. It creates a sense that “this person gets me” on a fundamental level.

Shared Behavioral Traits (Personality and Habits)

What counts as behavioral traits? This category covers personality characteristics (like being extroverted or introverted, laid-back or Type A, adventurous or cautious) as well as day-to-day behavioral habits and lifestyle preferences. For example, two people might have a similar sense of humor, level of optimism, or approach to organization and routines. It can also include social behaviors – are you both non-smokers, do you both love partying every weekend, or are you both homebodies? In essence, these are similarities in how you behave and interact with the world.

Impact on friendship: We often feel more comfortable around people with a similar temperament. An energetic, outgoing person may naturally click with someone equally social, while two quieter, introverted people might enjoy each other’s calm company. Indeed, research on friendship formation shows that we’re inclined to form close friendships with people we perceive to have personality traits similar to our own . In new friendships, a sense of “chemistry” can come from matching wavelengths – maybe you’re both jokesters, or both nerd out over intellectual debates, or you’re both free-spirited and spontaneous. Additionally, behavioral similarity in the sense of lifestyle can facilitate friendship: if you both like a similar pace of life or have compatible habits (say, both early risers who prefer hikes over nightclubs), it’s easier to spend time together without one person compromising. There’s also evidence of selection by personality in friend groups. For instance, people tend to choose friends with a similar level of extraversion (outgoingness) as themselves 【36†L17-L24**】 (extroverts find each other at the party, while introverts might bond in a quieter setting). However, how much does personality similarity actually matter for maintaining a friendship? Perhaps less than we’d assume. A recent study of ~200 long-term friend pairs in Germany found something surprising: friendship satisfaction was unrelated to how similar the two friends were in Big Five personality traits. In other words, once a friendship is well-established (the friendships in that study averaged 10 years long), having similar personalities didn’t impact how happy they were with the friendship. The researchers concluded that personality resemblances might help spark a friendship initially – a correspondence in certain traits can draw people together – but over time, personality similarity “wanes in importance” for the bond’s quality . As friendships deepen, other factors (like trust, support, and shared experiences) carry more weight, and friends often learn to accept each other’s differences . So, two very different people can absolutely remain best friends if they’ve built a strong base of understanding. In short, similar dispositions can be a social lubricant early on, but they aren’t a strict requirement for enduring friendship.

Impact on romantic relationships: Do opposites attract when it comes to personality, or do like-minded personalities make for happier couples? Research leans toward the latter, but with a twist. It’s well documented that spouses and romantic partners show some similarity on broad personality traits, but the effect is not very strong. In fact, one large review concluded that romantic partners are only modestly similar in personality on average – much less than they tend to be similar in beliefs or intelligence. Assortative mating (pairing with like individuals) for personality yields only small correlations (around r = 0.10) , which is quite low. So, plenty of couples have dissimilar personalities. Does that hurt relationship success? According to multiple studies, having similar personalities does not reliably predict higher relationship satisfaction . For example, a 2023 study of over 1,200 couples found that similarity on Big Five traits had no robust association with either partners’ relationship happiness or life satisfaction . Other work has found the same negligible effect (or only very tiny benefits of personality matching) for marital satisfaction . This goes against the common assumption that you need to be personality twins to get along – evidently, you don’t. What seems to matter more is having certain positive traits (like high agreeableness or emotional stability) in your partner, rather than them being a mirror image of you. As long as both partners are good-natured and supportive, differences in introversion or conscientiousness might not be dealbreakers. That said, there are specific behavioral compatibilities that can ease a relationship. For instance, similarity in general activity level or lifestyle preferences (sometimes called “behavioral homophily”) can reduce conflict. If both people enjoy similar day-to-day activities – whether that’s going out every weekend or prefer quiet evenings – it’s simpler to coordinate life. Likewise, sharing habits like spending style or approach to health (e.g. both are fitness enthusiasts, or neither minds a messy house) may reduce potential friction. Couples often naturally negotiate differences in these areas, but some research suggests having too many lifestyle mismatches (say one partner loves constant social outings while the other is a homebody) can strain satisfaction. Overall though, personality/behavioral similarities are nice-to-have but not critical for romance. They might help a couple initially “click” and make cohabiting smoother, but many couples thrive despite personality differences by practicing good communication and compromise. In fact, some differences can even be complementary (a pragmatic person balancing a dreamer, etc.), though true complementarity – where one’s strengths fill the other’s gaps – is less common than random chance.

Comparing friendships vs. romance: Personality and behavior play a role in attraction in both domains, especially at the outset. Friendships often form between people who perceive each other to be on the same wavelength , and romantic sparks can fly when you find someone who “just gets” your humor or way of life. However, both friendship and marriage research converge on the point that actual similarity in these traits is not a strong predictor of long-term happiness . Close friends and loving partners seem able to bridge personality differences through understanding and acceptance. It appears that sharing values and interests (common goals, likes, and worldview) is more crucial than sharing whether you’re both introverts or both love rigid schedules. So, while friends and lovers often have some matching quirks (and will playfully note their “twin” tendencies), a great relationship can also be like puzzle pieces fitting – not identical shapes, but complementary ones.

Shared Skills and Interests

What counts as shared skills/interests? This includes having the same hobbies, talents, or pursuits – for example, both partners being passionate about cooking, two friends who are musicians in a band, or a couple of gamers who love playing the same video games. It also covers participation in the same activities (sports, artistic endeavors, volunteer work) or shared expertise/skills (both engineers, both speak a second language, etc.). In short, it’s the overlap in what you do and enjoy.

Impact on friendship: Common interests are often the spark that ignites a friendship. Think about how many of your friendships started because you were on the same sports team, in the same chess club, or simply realized you both geek out over Lord of the Rings. Having activities you both enjoy gives you an easy way to spend time together and bond. Psychologists note that shared activities and interests create opportunities for positive interactions, mutual learning, and the inside jokes and shared experiences that form the glue of friendship . In surveys, people frequently cite common interests as one of the top reasons they became friends with someone. For instance, a YouGov poll found that a large majority of Americans like to make friends based on shared interests and values . Simply put, it’s fun to hang out with someone when you both love the same things – whether that’s hiking, thrifting vintage clothes, or debating philosophy. This is why clubs, fandoms, and hobby groups are such fertile ground for friendships; they gather like-minded folks together. Shared skills can also breed admiration and respect between friends (“My friend and I both do pottery, I really appreciate her artistic skills”). On the flip side, when friends have zero overlapping interests, they might struggle to find activities to do together, which can limit the friendship’s depth or longevity. Of course, many friends maintain a bond just through shared history or mutual support, even if their day-to-day interests diverge. But having at least some common interests tends to make friendships more enriching and enduring.

Impact on romantic relationships: “Couples who play together, stay together.” This saying holds some truth – sharing hobbies or leisure activities with a partner is linked to higher relationship satisfaction. A 2015 Pew survey of married Americans found that 64% said having shared interests is very important for a successful marriage . In fact, this ranked as the number one factor people mentioned, even above having a good sex life or financial stability. Enjoying activities together – whether it’s cooking, traveling, gaming, or working out – gives couples regular doses of positive experiences. According to relationship researchers, doing fun or challenging things as a duo can deepen intimacy by creating a sense of partnership and “self-expansion” (you grow together by learning new things) . Experimental studies have shown that couples assigned to engage in exciting new activities had greater increases in marital satisfaction compared to couples sticking to mundane routines . Even simple shared leisure like a weekly movie night or walking the dog together can strengthen a couple’s connection by fostering communication and teamwork. Conversely, lack of common interests can become a source of distance or conflict. In counseling surveys, “no common interests” is frequently cited as a contributor to breakups . One analysis of divorcing couples found that not sharing hobbies or recreational preferences was listed as a major reason for the split . It’s easy to see why: if one partner loves to ski every weekend and the other hates skiing (an example described by a therapist ), resentment or loneliness can build up. The ski-lover might feel held back, while the non-skier feels left out – a dynamic that can erode a relationship. Of course, couples don’t need to do everything together. It’s healthy to have some separate interests. Many partners compromise by pursuing their individual hobbies and cultivating a few shared ones. The key is that both people are comfortable with the balance. If each respects the other’s passions (maybe one goes skiing with friends while the other pursues their own hobby, then they cook dinner together – a shared activity), it can work out fine. But if neither person is willing to engage in any of the other’s interests, they may drift apart.

Comparing friendships vs. romance: In friendships, shared interests are arguably the strongest driver of who becomes friends. Unlike family or work relationships that exist by circumstance, friendships are voluntary – we usually choose friends we enjoy doing things with. A large-scale social study noted that having just one or two strong common interests can cement a friendship even if other backgrounds differ . In romantic relationships, shared interests may not be the initial spark (physical attraction often is), but they become very important in keeping the couple close and happy long-term. Both life domains benefit when people “play” together: laughter, novelty, and mutual passion act as social glue. One difference is that friends can have a great relationship centered on a single mutual interest (e.g. tennis buddies who only really connect on the court), whereas life partners generally need a broader alignment in how they want to spend free time together. In marriages, having nothing to do together for fun can be lethal to intimacy over the years. Thus, skill-based and interest-based similarity is a huge plus for any relationship. It doesn’t mean you must share every hobby – learning from each other’s unique interests can be rewarding too – but having some overlap in what brings you joy makes bonding much easier. As one psychologist succinctly put it: when two partners have the same or similar passions, it can bond them for years .

Shared Physical Attributes

What counts as physical attributes? These are observable physical characteristics – things like physical attractiveness, facial features, body type, height, ethnicity/race, and general appearance. It can also include style or the way one presents themselves (though that borders on behavior). In the context of similarity, we’re looking at traits like being of the same race or ethnic background, being of similar attractiveness level, or even having similar health/fitness habits that manifest physically.

Impact on friendship: Unlike the other categories, physical similarity is usually not the primary basis for friendship formation – people don’t typically choose friends because of how they look. However, physical attributes can indirectly influence friendships through social contexts. For example, race and ethnicity often correlate with friendship networks simply because of social environments and comfort levels (people of the same background may be drawn together due to cultural understanding). In fact, classic research on homophily found that American friendships show strong sorting by race, gender, and age, largely due to opportunities to meet and shared cultural experiences . Those are physical/demographic traits that people see and often use (consciously or not) as signals of commonality. Beyond demographics, consider attractiveness: Do people befriend others who are similarly attractive? There’s some evidence of an “attractiveness cluster” effect in social groups, but it’s not a hard rule. One small study back in the 1960s intriguingly found that college roommates who became friends had more similar levels of attractiveness than randomly assigned pairs . The idea is that highly attractive individuals might gravitate to each other’s company (perhaps due to moving in the same social circles or receiving similar social attention), and likewise for less-attractive individuals. However, this effect is not very pronounced in literature compared to romantic pairing. Friends come in all shapes and sizes, and a big disparity in looks doesn’t usually impede platonic affection the way it might affect dating choices. That said, perceptions of attractiveness can be influenced by friendship: interestingly, research shows that once people become friends, they tend to view each other as more attractive than strangers do . This “friendship effect” suggests that liking someone platonically can make you see them through rose-colored glasses physically – we find our friends beautiful because of who they are, not just how they look. All in all, physical attributes per se play a minor role in why friendships form; they’re more a side effect of other similarities (same race due to community, similar style due to shared subculture, etc.). We generally don’t pick our friends from a crowd based on appearance the way one might swipe on a photo for dating.

Impact on romantic relationships: In romance, physical attraction is often the gatekeeper for a relationship even starting. Offline, we initially approach or notice potential partners based on looks and observable traits. Thus, physical attributes – especially attractiveness – have a big influence on relationship formation. There is a well-documented “matching phenomenon” where people tend to couple up with others who are about equally attractive. In speed-dating and dating app studies, for example, couples’ similarity in attractiveness strongly predicts reciprocal interest and going on second dates . And in long-term pairings, you rarely see an extreme beauty paired with someone widely considered unattractive; partners usually match within a narrow attractiveness range. One study in Psychological Sciencedemonstrated that partners who got together soon after meeting were very similar in physical attractiveness, whereas couples who were friends for a while before dating showed less matching on looks . The interpretation is that when romance is decided quickly (love at first sight), people rely heavily on looks and end up with someone roughly as attractive as themselves. But if a pair builds a friendship first, other factors can override the physical “mismatch” – you might fall in love with a friend who isn’t your usual “type” because you’ve grown attached through non-physical qualities, so those couples are less look-matched . Beyond attractiveness, couples also tend to be similar in other physical traits. For instance, spouses show a moderate correlation in height and weight (~0.20) , meaning there’s some assortative mating for body size (perhaps due to both diet/exercise habits and preferences). People also often partner within their race/ethnic group – partly due to social proximity and cultural commonality, which ties back to shared beliefs and values. What about the strength of physical similarity effects? While initial attraction may depend heavily on physical appeal, research suggests that in long-term relationship success, physical traits are less influential than psychological ones. One study noted that people think physical attractiveness is crucial, but in practice they prioritizefinding a partner who shares their values and lifestyle over finding one who perfectly matches them in looks . That said, being on the same page about physical lifestyle can matter. If both partners place similar importance on fitness or appearance (for example, both are avid gym-goers, or neither cares much for strict diets), it can avoid conflict down the line. Physical intimacy also plays a role – if both are equally attracted to each other, it bodes well; if one partner greatly outshines the other in looks, it could potentially breed insecurity or jealousy from outside attention. But it’s important to note that overall compatibility can trump a difference in physical traits. Many happy couples have an “unequal” attractiveness pairing or different racial backgrounds; they simply have stronger connections in other areas that carry the relationship.

Comparing friendships vs. romance: Physical similarity is far more critical in romantic contexts than in friendships. Romantic attraction is often initially shallow (sparked by looks), whereas friendship attraction is typically based on deeper commonalities or simply repeated friendly interaction. Friends don’t need to think each other are physically attractive (and many don’t even consider it), but romantic partners usually do. Consequently, traits like attractiveness, style, or even things like age and race have greater impact on whom we date or marry than on whom we befriend. However, once relationships (of any kind) are established, physical factors tend to fade into the background. A friend who gains weight or a spouse who goes gray isn’t going to lose the bond that’s been built, because by then the relationship runs on more than appearances. One might say: looks may draw people together, but it’s the innersimilarities that keep them together.

Intellectual Similarities (Education & Intelligence)

What counts as intellectual similarities? This encompasses traits related to the mind and knowledge: having similar levels of intelligence or cognitive ability, similar educational backgrounds or degrees, and comparable intellectual interests (like a shared love for philosophy, literature, or scientific inquiry). It could be measured by formal education (for example, both friends are PhDs, or both spouses didn’t go to college) or by more informal markers of intellect (both are “deep thinkers” or both enjoy intellectual conversations).

Impact on friendship: Intellectual compatibility often underlies some of our most satisfying friendships. Many friendships form in school and university settings, which naturally pairs people with comparable education levels and academic interests. Studies of social networks find strong educational homophily – people are more likely to become friends if they have a similar educational standing, especially when friendships form in college or the workplace . Having a similar knowledge base or cognitive style can make communication easier between friends. Ever notice how people with shared geeky interests (say, two history buffs or two coding enthusiasts) can talk for hours? That’s intellectual bonding. Friends who operate on a similar intellectual wavelength may enjoy the same witty banter, exchange ideas fluidly, and validate each other’s thoughts. It’s gratifying to feel that a friend “gets” your jokes or references because they’re in the same intellectual ballpark. Intelligence itself (IQ) tends to be somewhat similar among friends, though this is tricky to measure outside of school grades. It likely happens because we are drawn to peers who challenge us just enough without boring or confusing us. If there’s too big a gap in intellectual level or educational experience, friends might find they have “different frequencies” – perhaps different tastes in conversation topics or leisure (one wants to discuss the latest science documentary, the other prefers celebrity gossip; nothing wrong with either, but it might limit mutual interests). However, many friendships happily bridge differences in education/intellect by focusing on other common grounds (workplace friendships between people in different roles, for example). A key point: respect is crucial. If both friends respect each other’s intellect, even if one’s a rocket scientist and the other an artist, the friendship can thrive through mutual admiration and learning.

Impact on romantic relationships: Assortative mating by education and intelligence is very strong in modern societies. People often meet their partners in educational environments (college, grad school) or within professions that require a certain education, which already skews matches toward similar educational backgrounds. Even beyond meeting opportunities, there is a tendency for individuals to select mates with comparable cognitive ability. Genetic research has found that spouse correlations for intelligence are around 0.40, which is higher than for almost any other behavioral trait . To put that in perspective, that correlation is stronger than spousal similarity in height or weight, and much stronger than for personality traits . This means that in general, smart people pair up with smart people at a notable rate. Similarly, educational homogamy (like two college grads marrying each other) is very common. Sociologists tracking marriage patterns over decades note that the share of marriages between people with similar education has risen, contributing to things like income inequality because two high-educated individuals combine their advantages . But from a relationship standpoint, why might intellectual similarity matter? For one, it can affect communication and shared activities. Couples with mismatched education or intellectual interests might find it harder to engage in stimulating conversation together or to fully appreciate each other’s perspectives. On the positive side, a well-matched intellectual pair can continually learn from each other and feel challenged in a good way. Shared intellectual pursuits (even just a mutual love of learning) can be a bond – e.g. academic couples or those who enjoy debate and discussing books. Values can also tie in: education often correlates with certain values or lifestyles, so similar education can mean similar outlook. However, intellectual similarity is not a strict requirement for love – plenty of couples with different educational levels have happy relationships, especially if they share values and respect one another’s intelligence (there are multiple types of intelligence, after all). Interestingly, one study found that what really matters is not necessarily actual IQ matching, but perceiving your partner as intelligent and capable . If both partners value intellect, each needs to feel the other is on their level in a way they esteem, even if in different domains (one might be book-smart, the other emotionally intelligent; if they appreciate each other’s smarts, it works). Large gaps, though, can cause frustration – for example, if one partner loves deep intellectual discussions and the other just isn’t interested, they may feel a mismatch in the “mind” part of the connection.

Comparing friendships vs. romance: Intellectual similarity strongly influences where friendships and romances happen: universities, professional fields, and interest-based groups tend to connect like-minded brains. The difference is that in romance, society places a bit more emphasis on matching by education/intellect because it often aligns with lifestyle and future goals (people may consider a partner’s education when thinking about marriage or child-rearing). In friendships, intellectual similarity mainly affects how close or personal the friendship becomes – acquaintances might enjoy small talk, but close friends usually need to feel they can truly communicate and understand each other, which is easier with similar intellect or knowledge. Both friendships and romantic partners benefit from being “equals” intellectually in terms of mutual respect and understanding. If there is a pronounced imbalance (say one party consistently feels the other can’t relate to their thoughts), the relationship might suffer. But when you find a friend or partner who can finish your sentences or eagerly dive into your favorite cerebral hobby with you, it’s a special kind of bond. Many couples describe their spouse as their best friend and someone they can talk to about anything – that reflects intellectual and emotional partnership. Indeed, research in Molecular Psychiatry pointed out that assortative mating is greater for intelligence than for personality , underlining that humans strongly value meeting of the minds in long-term mates. In summary, sharing intellectual traits and curiosity provides fertile soil for both friendships and love to grow, often fueling the most profound conversations and mutual growth in a relationship.

Which Similarities Matter Most?

Clearly, similarity overall is a powerful force in relationship formation. But are some shared traits more influential than others? Research suggests beliefs/values and interests carry especially heavy weight in forging strong bonds, whereas personality and superficial traits carry relatively less weight for long-term success.

In romantic relationships, alignment on core values (religion, life priorities, politics) and lifestyle compatibility often emerges as make-or-break factors . Shared beliefs create a deep sense of unity and purpose, making this category arguably the most important for durability. Intellectual and educational similarity also ranks highly – it’s one of the strongest assortative mating patterns and can affect long-term harmony in communication and goals. Physical attractiveness is most crucial at the formation stage of romance (you need that spark to get started), but its importance diminishes over time relative to emotional and value compatibility. As one study elegantly showed, if a couple’s relationship began platonically, the influence of looks on partner choice was much lower . So while a minimum level of mutual attraction is necessary for romance, matching on looks is not what keeps love going; shared values and interestsdo. Personality similarity is pleasant, but multiple studies indicate it’s a relatively weak predictor of relationship quality in both friendships and marriages . What matters more is having generally positive personality traits (e.g. kindness) and the ability to appreciate each other, rather than both being, say, equally orderly or equally adventurous.

For friendships, shared interests and activities are often the strongest glue at the start – this is how most friendships initially form (you spend time on something together). Shared values bolster friendships too, especially close ones; many best friends talk about “seeing the world the same way.” Demographic and physical similarities (like race or age) often simply reflect the social contexts in which friendships form , but by themselves they don’t guarantee a close friendship. Personality fit can help friends get along (e.g. two easygoing people may have fewer conflicts), but friends can also delight in personality differences more easily than romantic pairs, perhaps because the expectations in friendship are a bit more flexible.

Interestingly, having many similarities doesn’t infinitely increase attraction – there may be diminishing returns. A social network analysis of adolescent friends found that while each additional shared attribute did raise the likelihood of friendship, the benefit of each new similarity got smaller . In other words, if two people already share a lot (say, same school, same religion, same hobby), adding one more similarity (like both play guitar) isn’t as impactful as it would be for two people who differ in most other respects. This implies that even one or two strong commonalities can be enough to form a bond – you don’t have to be twins in everything. Often, a key similarity in a domain that matters to both people (a shared passion or a core value) is the foundation, and other differences can be navigated.

Bottom line: Shared beliefs/values and interests seem to be the heavyweight champions of relationship-building – they foster trust, mutual understanding, and enjoyment, which are the bedrock of any close relationship . Intellectual parity is also highly influential, especially in romantic partner choice , as it affects communication and lifestyle alignment. Physical attractiveness plays a strong role in initial romantic attraction , but much less so for platonic friendship and long-term stability. Personality/behavioral similarities have more nuanced, modest effects: they can help early rapport but are not strictly necessary for a satisfying friendship or marriage . Ultimately, the strongest relationships often have a balance of similarities – enough common ground to feel connected, with enough differences to keep things interesting and allow each person to grow. So, while birds of a feather do flock together, each bird might bring its own color to the flock. The science says: finding someone like you in the ways that count can indeed be a recipe for lasting friendship and love – and it’s those deeper shared traits that help keep the bond when life’s storms hit.

Sources:

• McPherson, M., Smith-Lovin, L., & Cook, J. M. (2001). “Birds of a feather: Homophily in social networks.”Annual Review of Sociology, 27, 415-444. [Discusses homophily patterns in age, race, religion, etc., in Americans’ social ties]

• Block, P., & Grund, T. (2014). “Multidimensional homophily in friendship networks.” Network Science, 2(2), 189-212. [Found that each additional shared attribute between friends yields smaller marginal gains in tie formation]

• Hibbing, J. R., Alford, J. R., et al. (2014). “Assortative mating and political orientation.” Journal of Politics. [Reported that spouses heavily sort on politics; political similarity was stronger than similarity in personality or appearance among thousands of couples]

• Gordon, A. M., et al. (2024). “I love you but I hate your politics: Dissimilarity in political attitudes and romantic relationship outcomes.” Journal of Personality and Social Psychology. [Large study of ~4,000 individuals: most couples shared political beliefs; those who didn’t had slightly lower relationship quality]

• Van der Wal, R., et al. (2024). “Values in romantic relationships.” Pers Soc Psychol Bulletin, 50(7), 1066-1079. [Showed the importance of personal value orientation (self-transcendence values) for one’s own relationship quality.]

• Christakis, N. A., & Fowler, J. H. (2014). “Friendship and natural selection.” PNAS, 111(3), 10796-10801. [Found friends have genetic/phenotypic similarities, including a tendency for similar traits like olfactory genes (indirectly related to physical/biological trait similarity).]

• Hunt, L. L., Eastwick, P. W., & Finkel, E. J. (2015). “Leveling the playing field: Longer acquaintance predicts reduced assortative mating on attractiveness.” Psychological Science, 26(7), 1046-1053. [Demonstrated that couples who knew each other longer pre-dating showed less similarity in attractiveness, implying other factors compensated for looks] .

• Körner, R., & Altmann, T. (2024). “Personality and friendship satisfaction in long-term friends.” Journal of Social and Personal Relationships. [Found no effect of actual personality similarity on friendship satisfaction, suggesting perceived similarity matters more initially] .

• Weidmann, R., et al. (2023). “Trait and facet personality similarity and relationship and life satisfaction in romantic couples.” Journal of Research in Personality, 104. [Large sample study confirming that personality similarity has negligible impact on partners’ relationship satisfaction] .

• Pew Research Center (2015 & 2019 surveys). [Reported 64% of married Americans say shared interests helped their marriage succeed , and 88% say love is key reason to marry (for context). Also documented increasing educational assortative mating trends.]

• Plomin, R., & Deary, I. J. (2015). “Genetics and intelligence differences: five special findings.” Molecular Psychiatry, 20, 98-108. [Notes that assortative mating for intelligence is about r≈0.40, higher than for other traits like personality or height] .

• Reissman, C., Aron, A., & Bergen, M. (1993). “Shared activities and marital satisfaction: Causal direction and self-expansion versus boredom.” Journal of Social and Personal Relationships, 10(3), 243-254. [Classic experiment where couples doing novel exciting activities showed boosts in marital satisfaction] .

• Wiesel, M., et al. (2022). “Perceived general similarity and relationship satisfaction: The role of couples’ shared stories.” Personal Relationships, 29(3), 549-568. [Highlights that perceived similarity (feeling like you have a lot in common) is linked to higher satisfaction, regardless of actual trait matching].

• Maoz, I., & Ellis, S. (2008). “Intergroup communication as a predictor of Jewish-Israeli agreement with integrative solutions to the Israeli–Palestinian conflict: The mediating effects of out-group trust and guilt.”(Note: included to illustrate the importance of shared perspectives in conflict resolution – indirectly relevant to belief homophily).