It is important to understand how homophily changes the way we think
Birds of a feather tend to shop together. That we know. They also tend to talk together and walk together; and who their friends are affects more than just what type of jeans they buy. Their friends have the capacity to affect their tastes, activities, and their lives overall. Sociologists call this phenomenon of being affected by one's friends "homophily" -- the tendency to associate with people similar to you and the people you associate with tend to act like you over time (and vice-versa).
Humans naturally conform to social influence -- to their surroundings, environment, strangers, peers, friends, and the like. People tend to socially conform or mimic their friends' behaviors, attitudes, etc. Besides the need for information, it is understood that people conform so that they will be liked and accepted by other people.
We tend to associate ourselves with those who are similar to us in interests, attitudes, values, background, and personality. The old saying that "opposites attract" doesn't hold much weight; research evidence by Miller McPherson shows that it is similarity that draws people together (imagine starting with another Custom Field 5 on social networks like Custom Field 6 you).
The Effect Your Friends Have Over You
Your peers are very important. Judith Rich Harris's groundbreaking book, The Nurture Assumption, suggests that peers have a much greater influence on child development than parents or teachers. An immigrant 4-year-old boy from Poland (or China) who just moved to St. Louis is more likely to speak perfect English and love baseball within a year because he wants to fit in with the other kids. He might still like traditional Polish food, but he'll also quickly love hamburgers and pizza.
The social psychology phenomenon of "mirroring" -- people that are your friends or people that like you in general, tend to physically mimic or mirror your behavior, vernacular, movements, etc. -- is example of the type of subconscious influence your friends have over you. As a social experiment, try incorporating a new word or phrase into your lexicon and notice how your friends will slowly adopt and use this word or phrase. Or try crossing your arms during a conversation with one of your friends and see if they mimic that behavior.
On a gender basis, women are slightly more prone to be influenced by their female friends than men are by their male friends. In her research Sex Differences in Social Behavior, Alice Eagly hypothesizes that this stems from the social roles men and women are taught in our society.
How Your Friends Affect Your ...
Nick Christakis and James Fowler published a study last year in the New England Journal of Medicine which suggests that your friends greatly affect your health. According to the study:
A person's chances of becoming obese increased by 57% if he or she had a friend who became obese in a given interval. Among pairs of adult siblings, if one sibling became obese, the chance that the other would become obese increased by 40%. If one spouse became obese, the likelihood that the other spouse would become obese increased by 37%. These effects were not seen among neighbors in the immediate geographic location.
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