Final answer:
Marriage is a legally recognized social contract between two people, traditionally based on a sexual relationship and implying a permanence of the union. It addresses challenges within families and varies across societies with different cultural practices.
Step-by-step explanation:
Marriage is a legally recognized social contract between two people, traditionally based on a sexual relationship and implying a permanence of the union. It serves as an effective means to address challenges within families, such as providing a structure to produce, raise, and nurture offspring, reducing competition, and creating a stable socioeconomic household. The rules of marriage, including endogamy and exogamy, vary across societies. While variations exist, marriage is a universal institution with different cultural practices.