Abstract

Objectives: In China, the recent replacement of the one-child policy with a twochild

policy could potentially change family ecology—parents may switch investment

from exclusively one child to two. The parent-offspring conflict theory provides

testable hypotheses concerning possible firstborn opposition toward further reproduction

of their mother, and who wins the conflict. We tested the hypotheses that if there

is any opposition, it will differ between sexes, weaken with offspring age and family

resource availability, and affect maternal reproductive decision-making.

Methods: Using survey data of 531 non-pregnant mothers of only one child from

Xi’an (China), logistic regression was used to examine effects of age, family income,

and sex on the attitudes of firstborn children toward having a sibling; ordinal regression

was used to investigate how such attitudes affect maternal intention to reproduce

again.

Results: Firstborns’ unsupportive attitude toward their mothers’ further reproduction

weakened with age and was overall more frequent in low-income families. Sons’

unsupportive tendency displayed a somewhat U-shaped relationship, whereas daughters’

weakened with family income; consequently, sons were more likely than

daughters to be unsupportive in high-income families, suggesting a tendency to be

more demanding. Forty-nine percent of mothers supported by their firstborns

intended to reproduce again, whilst only 9% of mothers not supported by firstborns

had such an intention.

Conclusion: Our study contributes to evolutionary literature on parent-offspring conflict

and its influence on female reproductive strategy in modern human societies, and

has also important implications for understanding fertility patterns and conducting

interventions in family conflict in China.