The Pew Research Center recently released data on stepfamilies in the U.S. Of the 2,691 respondents, over 40% had at least one step relative in the immediate family:
Note that they include both step- and half-siblings. For readers who might not be familiar with that language, a step-sibling is related to you only through marriage; you don’t share a biological parent. A half-sibling shares one parent with you, but not both. I can see the point of including both categories if you’re interested in seeing the degree to which American family life varies from the culturally-accepted “ideal” nuclear family, but I would think putting both in a single category might hide meaningful differences (such as for the question about obligation, below).
The chances of having a step-relative in the immediate family vary quite a bit based on demographics, reflecting differences in marriage, divorce, and non-marital childbearing rates:
The vast majority (70%) of people with step-relatives said they were very satisfied with their family lives, undermining some of the cultural stereotypes of stepfamilies as inherently filled with conflict. However, the survey also asked participants if they would feel “obligated” to help a family member who was facing serious problems and needed either financial help or caregiving. The results show more feelings of obligation to biological family members than to step-relatives:
I presume perceptions of obligation vary widely based on how old a person was when their parent married their stepparent, the quality of the relationship, and perhaps even whether the stepparent has biological children. The data would seem to have important implications for our ability to draw on family networks for resources. Who is responsible for caring for elderly parents, for instance? Only their biological children? Should someone feel obligated to help a person who they’re related to only because of a parent’s marital choice? Unclear cultural norms about obligations to step-relatives bring up a number of complex issues that many Americans will be forced to grapple with in the future.