The Family Scoreboard

THE BELIEF

“Sibling rivalry is something you outgrow once you're an adult with your own family.”

THE DATA

Young adults in their twenties and thirties still report perceiving differential parental treatment, and comparison with siblings continues to be measurable — and to affect wellbeing — into mid- and later life.

THE BELIEF

“If your spouse's siblings compete with or exclude you, it means something is specifically wrong with you.”

THE DATA

Evolutionary kinship theory treats friction between in-laws as a predictable structural feature of blended kin systems — affinal relatives don't automatically share the same stake in each other's welfare that blood relatives do, so rivalry over a shared relative's attention is a system-level pattern, not proof of a personal flaw.

THE BELIEF

“Parents don't really have favorites — that's just how it feels to the less-favored child.”

THE DATA

A 2025 meta-analysis of nearly 19,500 participants across dozens of studies confirms differential parental treatment is real, measurable, and patterned — by the child's gender, birth order, and personality — not a distortion of perception.