Brothers delay menarche and the onset of sexual activity in their sisters

The higher costs of sons compared with daughters extends to a negative effect of brothers on the lifetime reproductive success of their siblings in subsistence and preindustrial societies. In societies with fewer resource constraints, one might expect that these effects would be limited or non-exist...

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Bibliographic Details
Published in:Proceedings of the Royal Society. B, Biological sciences Biological sciences, 2011-02, Vol.278 (1704), p.417-423
Main Authors: Milne, Fritha H., Judge, Debra S.
Format: Article
Language:English
Subjects:
Adolescent
Adult
Age Factors
Aged
Birth Order
Brothers
Children
Cohort Studies
Costs Of Brothers
Daughters
Female
Helper-At-The-Nest
Humans
Male
Menarche
Menarche - physiology
Menarche - psychology
Middle Aged
Mothers
Onset Of Sexual Activity
Pregnancy
Proportional Hazards Models
Reproduction
Reproductive success
Retrospective Studies
Sexual Behavior - physiology
Sexual Behavior - psychology
Sexual intercourse
Siblings
Sisters
Sons
Western Australia
Young Adult
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Summary:The higher costs of sons compared with daughters extends to a negative effect of brothers on the lifetime reproductive success of their siblings in subsistence and preindustrial societies. In societies with fewer resource constraints, one might expect that these effects would be limited or non-existent. This study investigates the costs of brothers and sisters in a contemporary western society of adult Australians. Girls with elder brothers had a delayed age at menarche. Younger brothers were associated with delayed onset of sexual activity in sisters, but not in brothers. Neither younger nor elder brothers influenced fitness parameters (number of pregnancies, number of children, age at first pregnancy or age at first birth) in siblings of either sex. This study provides evidence that brothers negatively affect their sisters' onset of reproductive maturity and sexual activity; however, this delay is not associated with a fitness cost in contemporary Australia. We suggest this is due to the long period of independence prior to child bearing.
ISSN:0962-8452
1471-2945
1471-2954
DOI:10.1098/rspb.2010.1377