Final answer:
Most people choose a spouse based on similarity, best described by the saying "birds of a feather flock together."
Step-by-step explanation:
The saying that best sums up how most people choose a spouse is "birds of a feather flock together." This proverb implies that people are attracted to others who are similar to themselves in various aspects such as background, attitudes, and lifestyle. Research supports this concept, often referred to as homophily, which dictates that similarity plays a crucial role in the formation and maintenance of relationships. It is easier to connect and form a lasting bond with someone who shares common interests, values, and cultural backgrounds.