回答下列各题： Marriage emerged as the most popular institution throughout history primarily because it was an effective arrangement to improve the care and upbringing of children. Marriage is not necessary to have children, but it has been of enormous importance in the rearing of children. With the sharp declines in birth rates since 1970 in Western and other rich countries, including much larger fractions of adults who do not have any children, both men and women have significantly increased their ages marriage, and sharply raised their tendencies to divorce. In 1950, a typical woman and man married at ages 20.3 and 22.8 respectively, whereas now the typical marital ages are 26.0 and 27.7. These changes in age at mariage are related to reduced demand for many children, increased college education of both men and women but especially of women, much greater labor force participation of married and divorced women, and the narrowing of the gender gap in earnings. The most important economic and social concerns due to low marriage rates are the effects on roaring of children. These effects are not due to lower marriage rates alone, but rather to the close connection between these low rates and high divorce rates, and to the greater tendency of women to have children without being married, or without living with the fathers of their children. Although many single mothers do an absolutely wonderful job in raising their children, common sense and most academic findings suggest that having a father present during the raising of children generally has a positive effect on the development of non-cognitive ( 非认知性) traits of children, These include a general respect for authority and reduced rebelliousness in school, and the avoidance of gangs and other criminal activities. It also appears that the absence of fathers has a greater effect, on the non-cognitive traits of sons than daughters, although that is a less well-established finding. I am not claiming that children are worst oft' when their parents divorce if their parents were fighting a lot, or ff they bad abusive (粗暴的) fathers. Rather, it, appears that up to a significant point, children are, better off in intact families even when their families are not ideal. What do we learn from the first paragraph about marriage?