It's a girl: why fathers of daughters may invest more in their relationships

Parents often say a child changes everything about their relationship. A recent study in Personality and Individual Differences suggests one change may track something parents cannot choose, namely whether they have a son or a daughter. Across three datasets, fathers of daughters showed stronger commitment and attachment to their child's mother than fathers of sons did. Mothers showed no comparable difference.

Krystal Duarte, Kristina Durante and colleagues analysed data from 1,694 parents. Study 1 compared the self-reported relationship quality of fathers and mothers raising a daughter or a son. Study 2 followed 587 couples in a long-running US cohort from their child's birth to age nine. Study 3 tracked 168 first-time-parent couples from late pregnancy to two years after the birth.

The pattern held across all three. Fathers of daughters reported higher attachment security, greater commitment and more partner-directed support than fathers of sons, and mothers were more likely to report receiving that support. Importantly, none of these differences appeared for mothers, whose reports did not vary with the sex of their child.

The researchers interpret this through paternal investment theory. Decades of work links low-quality or absent fathering to earlier puberty, earlier sexual activity and less stable relationships, and these effects are particularly pronounced for daughters. Most of that research asks how fathers shape daughters. This study turns the question around and asks whether having a daughter shapes fathers, prompting them to model a stable partnership.

The strongest evidence comes from Study 3, because it measured change within the same men. Before the birth, fathers of sons and fathers of daughters did not differ. After the birth, fathers of daughters became less anxiously attached to their partners and maintained their relationship satisfaction, while fathers of sons did not show the same pattern. Because the shift followed the birth rather than preceding it, it is harder to explain as a pre-existing difference between the two groups of men.

One qualification is worth noting. The bond linked to having a daughter appeared to weaken as children grew older, echoing the broader father-absence literature, in which early childhood seems to be the most consequential window. In the US cohort, the partner support reported by fathers of sons gradually increased over time, narrowing the initial gap.

None of this means that fathers of sons are less devoted to their partners, or that a child's sex sets a relationship's course. The researchers are careful to present this as one plausible signal among many, and personality, circumstance and relationship history all still matter a great deal. The findings are also correlational and drawn from Western samples, so they may not generalise everywhere.

Still, the work adds an intriguing evolutionary dimension to how families form. A child's sex does not determine a relationship's fate. What the study suggests is subtler, that becoming a parent can recalibrate how partners support each other in ways they may not notice at the time.

Duarte, K., Durante, K. M., Gassen, J., Reed, A., Rholes, S., & Simpson, J. A. (2026). Daughters promote pair-bonding in fathers in modern Western cultures. Personality and Individual Differences, 262, Article 113901. https://doi.org/10.1016/j.paid.2026.113901