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Birth order and fluctuating asymmetry: a first look
M L Lalumière1, G T Harris, M E Rice
1Mental Health Centre Penetanguishene, Ontario, Canada. martin_lalumiere@camh.net
Proceedings. Biological Sciences
|January 22, 2000
Summary
Maternal immune responses to male fetuses may increase developmental instability. More older brothers correlated with higher fluctuating asymmetry in adult males, suggesting a link between prenatal exposure and physical development.
Area of Science:
- Evolutionary biology
- Developmental biology
- Human reproduction
Background:
- Maternal immune responses during pregnancy are crucial for fetal development.
- Prenatal exposure to maternal hormones and immune factors can influence offspring development.
- Fluctuating asymmetry (FA) is a measure of developmental instability.
Purpose of the Study:
- To test the hypothesis that maternal immunoreactivity to male-specific fetal antigens increases developmental instability.
- To investigate the relationship between the number of older brothers and fluctuating asymmetry in adult males.
Main Methods:
- Assessed fluctuating asymmetry in ten bilateral morphological traits in adult males.
- Collected data on the number of older and younger siblings (brothers and sisters).
- Compared FA scores and sibling data between psychiatric patients and hospital employees.
Main Results:
- A positive association was found between the number of older brothers and fluctuating asymmetry.
- This relationship was consistent across both psychiatric patients and hospital employees.
- Psychiatric patients exhibited higher FA scores and a tendency for more older brothers than controls.
Conclusions:
- Maternal exposure to male-specific antigens may contribute to developmental instability.
- The number of older brothers serves as a proxy for cumulative prenatal exposure to male-specific factors.
- Findings suggest a potential biological basis for observed differences in developmental stability.
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