Final answer:
The principle shown in people forming romantic relationships with those of similar social classes and racial-ethnic backgrounds is homogamy. Homogamy entails connecting with those who share similar backgrounds and life experiences, while homophily refers to the general inclination to form social networks with similar individuals.
Step-by-step explanation:
The phenomenon where people of similar racial-ethnic backgrounds and social classes tend to have more contact with one another and are more likely to enter into romantic relationships is an example of the principle of homogamy. Homogamy is the tendency for individuals to form connections, including friendships, marriage, and other types of relationships, with others who are similar to themselves. It is based on shared interests, values, social standing, and practices.
Homophily is a related concept and refers to the broader tendency for people to form social networks with others who are like them. This can lead to homogenous groups and limit exposure to diverse perspectives and experiences. In contrast, exogamous marriages are unions of spouses from different social categories and rely more on values such as love and compatibility rather than shared social characteristics.