Kin

Two demographic trends over the twentieth century, increases in life expectancy and decreases in fertility, have major implications for the number and type of relatives in individuals' kinship networks, as well as for the nature of kin relationships (Bengtson, Rosenthal, and Burton; Uhlenberg). With each successive birth cohort, a higher proportion of people survive to old age, and the duration of time spent in old age is increasing as well. As a result, middle-aged adults may have more older relatives in their kinship networks than was true in the past. As well, kin relationships extend over a longer period of time than they did in the past. For example, many grandparents now live into their grandchildren's adulthood.

Fertility is a key factor affecting the supply of kin. The number of children one has will, obviously, determine family size in later life, and whether one has many, few, or no children to whom to turn for help and emotional support. It will determine, as well, whether one has many, few, or no grandchildren. The number of children one's parents had determines whether one has many, few, or no siblings, as well as whether, in adult life, one will have siblings-in-law, nieces, and nephews. As older relatives—parents, aunts, and uncles—die, individuals with siblings will still have kin beyond their own children and grandchildren, and will thus have a larger kinship network than individuals who have no siblings. The birth rate declined considerably over the twentieth century. However, while the average number of children has declined, the key decline has been in the proportion of women having very large families (five or six children or more). There has been a corresponding increase in the proportion of women having two or three children. Peter Uhlenberg argues that, if we are concerned about the potential support to older parents, the important distinction is between having no children or only one child and having two or more. People now in old age and those who will enter old age in the near future will have two or more children, on average. This means that most middle-aged adults will have siblings as part of their kin group. In the more distant future, as baby boomers enter old age, the percentage of older people with one or no children will increase, although rates of childlessness among the old will still be lower than they were in 1990.