Homophily () is a concept in sociology describing the tendency of individuals to associate and bond with similar others, as in the proverb "". The presence of homophily has been discovered in a vast array of network studies: over have observed homophily in some form or another, and they establish that similarity is associated with connection. The categories on which homophily occurs include age, gender, class, and organizational role. The opposite of homophily is heterophily or intermingling. Individuals in homophilic relationships share common characteristics (beliefs, values, education, etc.) that make communication and relationship formation easier. Homophily between mated pairs in animals has been extensively studied in the field of evolutionary biology, where it is known as assortative mating. Homophily between mated pairs is common within natural animal mating populations. Homophily has a variety of consequences for social and economic outcomes. Types and dimensions Baseline vs. inbreeding To test the relevance of homophily, researchers have distinguished between two types: Baseline homophily: simply the amount of homophily that would be expected by chance given an existing uneven distribution of people with varying characteristics; and Inbreeding homophily: the amount of homophily over and above this expected value, typically due to personal preferences and choices. Status vs. value In their original formulation of homophily, Paul Lazarsfeld and Robert K. Merton (1954) distinguished between status homophily and value homophily; individuals with similar social status characteristics were more likely to associate with each other than by chance: Status homophily: includes both society-ascribed characteristics (e.g. race, ethnicity, sex, and age) and acquired characteristics (e.g., religion, occupation, behavior patterns, and education). Value homophily: involves association with others who have similar values, attitudes, and beliefs, regardless of differences in status characteristics. Dimensions Race and ethnicity Social networks in the United States today are strongly divided by race and ethnicity, which account for a large proportion of inbreeding homophily (though classification by these criteria can be problematic in sociology due to fuzzy boundaries and different definitions of race). Smaller groups have lower diversity simply due to the number of members. This tends to give racial and ethnic minority groups a higher baseline homophily. Race and ethnicity also correlates with educational attainment and occupation, which further increase baseline homophily. Sex and gender In terms of sex and gender, the baseline homophily networks were relatively low compared to race and ethnicity. In this form of homophily men and women frequently live together