Many younger siblings feel at a disadvantage to their older brothers and sisters at times, suffering earlier curfews and hand-me-down clothes, but a new study has found that the configuration of siblings within a family can have long-term socioeconomic effects, even across generations.
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Studies of families in modern, post-industrial societies have examined whether having brothers versus sisters affects children’s success in school, although the results have often been contradictory. Other research has shown that later-born children tend to fare worse in school and on IQ tests. One explanation could be that they receive less investment by parents, as time and resources are “diluted” by older siblings before and after birth; younger siblings contribute only later. A new study [available on MyScienceWork] adds to this research by looking, for the first time, at the sex of siblings and birth order in relation to a person’s socioeconomic situation as an adult—as well as the consequences for later generations.
David Lawson, now at the London School of Hygiene and Tropical Medicine, and colleagues compiled data from birth records and public registers for the city of Uppsala in Sweden. Starting with babies born between 1915 and 1929, they traced the families of these 10,000 or so individuals through their children and grandchildren. The socioeconomic success of each generation was measured according to three indicators: schoolmarks, entering university and family income. In analyzing the data, the researchers adjusted for other factors like parents’ socioeconomic situation and the mother’s age at the birth of the child.
Their results showed that the sex of one’s siblings had no impact on socioeconomic outcomes. On the other hand, the findings supported research on family size in general, showing that the larger the family, the less likely children were to enter university, for example. On top of that, sibling configuration—where a person fell in the birth order—had a significant impact on the level of education they attained: those born later (i.e. having more older siblings) were less likely to obtain a college education. What’s more, their own children were also less likely to attain higher levels of education, regardless of family size in this second generation.
Surprisingly, while it was related to educational attainment, the configuration of siblings in a family did not affect future income for individuals or their children. For the moment, the researchers don’t know why, but Lawson and colleagues speculate that growing up with more older siblings may carry advantages that only become apparent later in life. In a previous study of UK families, Lawson and colleagues found later-born children had better mental health, perhaps due to support from their older brothers and sisters. This could help them avoid certain problems in adulthood. It is also possible that growing up with older siblings somehow improve one’s ability to navigate social relationships, offsetting their educational disadvantage.
While this research does not directly imply a cause-and-effect relationship, understanding how these different factors interact could find important applications. The researchers believe the unequal outcomes seen for children within the same family, due to sibling configuration, could be as significant as the inequalities between families of different social classes. If the mechanisms can be revealed, interventions could be designed to limit the socioeconomic disadvantages, or even enhance the advantages, seen for the later-born.