Human Nature

, Volume 19, Issue 2, pp 189–210 | Cite as

Lineage, Sex, and Wealth as Moderators of Kin Investment

Evidence from Inheritances
  • Gregory D. WebsterEmail author
  • Angela Bryan
  • Charles B. Crawford
  • Lisa McCarthy
  • Brandy H. Cohen


Supporting Hamilton’s inclusive fitness theory, archival analyses of inheritance patterns in wills have revealed that people invest more of their estates in kin of closer genetic relatedness. Recent classroom experiments have shown that this genetic relatedness effect is stronger for relatives of direct lineage (children, grandchildren) than for relatives of collateral lineage (siblings, nieces, nephews). In the present research, multilevel modeling of more than 1,000 British Columbian wills revealed a positive effect of genetic relatedness on proportions of estates allocated to relatives. This effect was qualified by an interaction with lineage, such that it was stronger for direct than for collateral relatives. Exploratory analyses of the moderating role of benefactors’ sex and estate values showed the genetic relatedness effect was stronger among female and wealthier benefactors. The importance of these moderators to understanding kin investment in modern humans is discussed.


Genetic relatedness Inclusive fitness Inheritance Kin investment Lineage Prosocial behavior Resource allocation Wills 



We thank the staff of the Vancouver Probate Office for their assistance in helping us access the probated wills, and the Canada Manpower Summer Student Works Project, who paid the salaries of the students who worked on this project.

This material is based on work supported by the National Institute of Mental Health under Training Grant Award PHS 2 T32 MH014257 entitled “Quantitative Methods for Behavioral Research” (to M. Regenwetter, Principal Investigator). This research was completed while the first author was a postdoctoral trainee in the Quantitative Methods Program of the Department of Psychology, University of Illinois at Urbana–Champaign. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the National Institute of Mental Health.

This research was previously presented by the first author at the 17th annual meeting of the Human Behavior and Evolution Society in Austin, Texas, in June 2005.


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Copyright information

© Springer Science + Business Media, LLC 2008

Authors and Affiliations

  • Gregory D. Webster
    • 1
    Email author
  • Angela Bryan
    • 2
  • Charles B. Crawford
    • 3
  • Lisa McCarthy
    • 3
  • Brandy H. Cohen
    • 4
  1. 1.Department of PsychologyUniversity of Illinois at Urbana–ChampaignChampaignUSA
  2. 2.Department of Psychology/CASAA, MSC 03-2220University of New MexicoAlbuquerqueUSA
  3. 3.Department of PsychologySimon Fraser UniversityBurnabyCanada
  4. 4.Organizational Performance and Change, Colorado State University, Denver CenterDenverUSA

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