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Brothers and sisters : How sibling interactions affect optimal parental allocations
1Department of Anthropology, University of California, 95616, Davis, CA, USA. mborgerhoffmulder@ucdavis.edu.
Human Nature (Hawthorne, N.Y.)
|July 22, 2015
Summary
Parental investment in offspring varies by socioeconomic status and sibling composition. Poor families prioritize daughters
Area of Science:
- Anthropology
- Evolutionary Biology
- Human Behavioral Ecology
Background:
- Parental investment strategies are crucial for offspring survival and reproductive success.
- The Trivers-Willard hypothesis and local resource competition/enhancement models offer frameworks for understanding these strategies.
- Previous research has explored parental investment biases across different societies and socioeconomic strata.
Purpose of the Study:
- To test the Trivers-Willard and local resource competition/enhancement hypotheses using Kipsigis data from Kenya.
- To examine how parental investment in offspring (survival, education, inheritance) changes over the period of dependence.
- To investigate the influence of parental wealth and sibship composition on investment biases over time.
Main Methods:
- Analysis of age-specific survival, educational success, marital arrangements, and property inheritance data from the Kipsigis.
- Testing predictions derived from the Trivers-Willard hypothesis regarding parental investment biases based on offspring sex and parental wealth.
- Evaluating the local resource competition/enhancement hypotheses by examining the relationship between sibship size/sex composition and parental investment.
Main Results:
- Parental wealth did not significantly affect the survival rates of sons or daughters.
- A Trivers-Willard effect was observed in educational investment, with poorer families prioritizing daughters' schooling over sons', a trend that has increased over time.
- Parental investment in sons was influenced by the number of brothers (reduced investment) and sisters (increased investment), aligning with resource competition/enhancement models; investment in daughters showed less sensitivity to sibship composition.
Conclusions:
- Socioecological factors significantly shape parental investment biases, necessitating broad considerations in predictive models.
- The timing and nature of investment biases are influenced by the perceived value of children and the costs associated with parental investment.
- Careful selection of investment measures is crucial for accurate cross-sex and cross-class comparisons, explaining muted sex preferences in Africa compared to other regions.
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