"When parents are stricter with older children, it may be because evolution has favored parents who produce well-behaved older siblings who can help raise the younger ones," said lead author Christopher von Rueden, a professor of psychology at Concordia University in Montreal.
The researchers analyzed data from the Fragile Families and Child Wellbeing Study, a long-term study that has followed a diverse group of children and their families in 20 U.S. cities since birth. They found that parents reported being stricter with their firstborn children than their later-born children. This difference was even greater when the firstborn child was a boy.
The researchers speculate that the stricter parenting style with firstborn children may be due to a combination of factors. One possibility is that firstborn children are simply more likely to be exposed to younger siblings, which can lead to more conflict and misbehavior. Another possibility is that parents may have higher expectations for firstborn children, since they are the first child in the family and often seen as setting the standard for the younger siblings.
The researchers also found that parents who reported being stricter with their firstborn children tended to have more positive relationships with their children overall. This suggests that the stricter parenting style may be effective in promoting positive child development, at least in some families.
The findings of this study provide new insights into the role of older siblings in human evolution and development. They suggest that the unique challenges and opportunities of being an older sibling may have a lasting impact on the development of both older and younger siblings.
