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Sex differences in nepotism

Sex differences in nepotism. Trust in a trust game is associated with sex , exposure to baby’s and facial similarity. June 5, 2008. HBES 2008, Kyoto. Katinka Quintelier, Ghent University Katinka.Quintelier@UGent.be www.themoralbrain.be. Overview. Introduction & Predictions

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Sex differences in nepotism

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  1. Sexdifferences in nepotism Trust in a trust game is associatedwithsex, exposure to baby’s and facialsimilarity June 5, 2008 HBES 2008, Kyoto Katinka Quintelier, Ghent University Katinka.Quintelier@UGent.be www.themoralbrain.be

  2. Overview • Introduction & Predictions • Materials and Methods • Results • Discussion & Conclusions

  3. Overview • Introduction & Predictions • Materials and Methods • Results • Discussion & Conclusions

  4. The fossil record of the genus Homo (Wood & Collard, 1999) versus earlier hominins suggests: Slower maturation, prolonged development of children Increase in brain size Obligatebipedalism Increase in body size 1 Introduction Lake Turkana, Kenya Homo ergaster; Skull KNM-ER 3733 discovered by Bernard Ngeneo in 1975 (Kenya) • Wood & Collard, 1999. The Human Genus. Science ,284:65-71. • Antón, 2003.Natural History of Homo erectus.Yearbook of Physical Anthropology, 46:126-170. • Pictures: http://commons.wikimedia.org/wiki

  5. What also evolved since the emergence of the genus Homo: Shorter lactation period & interbirthinterval (Aiello & Key, 2002) Very long dependency of children Raisingseveraldependentchildrensimultaneously 1 Introduction Lake Turkana, Kenya Homo ergaster; Skull KNM-ER 3733 discovered by Bernard Ngeneo in 1975 (Kenya)  This could not have evolved without a co-evolving change in social life, i.e. assistance by others than the mother in child care. (Hrdy, 2005) • Aiello & Key, 2002. Energetic Consequences of Being a Homo erectus Female. American Journal of Human Biology, 14:551-565. • Hrdy 2005. Evolutionary Context of Human Development. The Cooperative Breeding Model.

  6. 1. Introduction • Whowouldassist a mother to decrease the burden of child care? • C < rB (Hamilton, 1964) • Father  paternal care • Kin  cooperativebreeding • “Cooperativebreeding is a breeding system in whichgroupmembers, otherthan the geneticparents (alloparents), help oneorbothparentsreartheiroffspring”. • Hrdy, 2005. • Hamilton, 1964. The genetic evolution of social behavior. J Theoretical Biology 7: pp. 17-18 • Geary, 2000. Evolution and Proximate Expression of Human Paternal Investment. Psychological Bulletin 126, 1:55-77. • Hrdy, 2005.

  7. 1. Introduction • Mother • Maternal grandmothers • Paternal grandmothers • Older siblings Sear and Mace, 2008. • Sear and Mace, 2008. Who keeps children alive? A review of the effects of kin on child survival. Evolution and Human Behavior 29:1-18. • E.g. Kramer, 2005. Children’s Help and the Pace of Reproduction: Cooperative Breeding in Humans. Evolutionary Anthropology 14:224-237.

  8. 1. Introduction • Women are expected to be more nepotisticthan men. Reproductive succescanbeincreased by : • Increasingsurvival of offspring (getting help fromkin) • Increasing inclusive fitness (helpingkin) • Increasingquantity of offspring • Some data support thishypothesis. • (LA) Womengive more help to and receive more help fromwealthyfemalekinwithchildren. (Essock-Vitale & McGuire, 1985) • (Canadian) Sistersrecalled more relatives and refered more to kinshipstatus in characterizingthemselves, thantheirbrothersdid. (Salmon & Daly, 1996) Neyer & Lang, 2003. Blood is Thicker Than Water: Kinship Orientation Across Adulthood. J PersSoc Psychol 84, 2:310-321. Salmon & Daly, 1996. On the importance of Kin Relations to Canadian Women and Men. Eth & Soc 17:289-297. Essock-Vitale & McGuire, 1985. Women’s Lives Viewed from an Evolutionary Perspective. II. Patterns of Helping. Eth &Soc 6:155-173.

  9. 1. Predictions • If we elicit a context of cooperative breeding, women will be more cooperative, at least when they are possibly related. • Female students will be more trusting towards another female, • When they are first exposed to pictures of baby’s • And when the other female looks subtly similar to them.

  10. 1. Predictions • Is facial resemblance a possible kinship cue? • Facial resemblance enhances trust (e.g. DeBruine, 2002). • Facial resemblance enhances cooperation (Krupp et al., 2008). • Facial resemblance of other-sex faces increases trust but decreases their attractiveness in the context of a short-term relationship (DeBruine, 2005). • An implicit evaluation of relatedness. • DeBruine, 2002. Facial resemblance enhances trust. Proc. R. Soc. Lond. B. 269: 1307-1312 • DeBruine, 2005b Trustworthy but not lustworthy: context-specific effects of facial resemblance. Proc. R. Soc. B. 272:919-922. • Krupp, DeBruine & Barclay, 2008. A cue of kinship promotes cooperation for the public good. Journal of Evolution and Human Behavior:49-55.

  11. Overview Introduction & Predictions Materials and Methods • Design • Participants • Stimuli • Procedure Results Discussion & Conclusions

  12. 2.1. Design Subject’ssex • 2 conditions Picture evaluationtask • 2 conditions: landscape or baby Trust game • 2 conditions: resemblance or no resemblance • « Player 2 » wasalwaysfemale! 2 x 2 x 2, all betweensubjects variables The entire program ranin «Presentation 12.1.»

  13. 2.1. Design Subject’ssex • 2 conditions Picture evaluationtask • 2 conditions: landscape or baby Trust game • 2 conditions: resemblance or no resemblance • « Player 2 » wasalwaysfemale! 2 x 2 x 2, all betweensubjects variables The entire program ran in «Presentation 12.1 »

  14. 2.1. Design Subject’ssex • 2 conditions Picture evaluationtask • 2 conditions: landscape or baby Trust game • 2 conditions: resemblance or no resemblance • « Player 2 » wasalwaysfemale! 2 x 2 x 2, all betweensubjects variables The entire program ran in «Presentation 12.1 »

  15. 2.1. Participants • 45 male, 47 female undergraduate students • Mean age = 21.54; s.d. = 2.97 • European

  16. 2.2. Stimuli • Trust game • Two conditions • Condition 1: player 2 resembles participant • Condition 2: player 2 does not resemble participant

  17. 2.2. Stimuli Facial Stimuli Database http://agingmind.utdallas.edu/ Player 2 Base face • Minear & Park, 2004. A lifespan database of adult facial stimuli. Behavior Research Methods, Instruments, & Computers, 36 (4):630-633.

  18. 2.2. Stimuli 50% Shape only transformation Player 2 Base face Player 2 Subject • Image manipulation software: Psychomorph (Tiddeman et al., 2005) • Transformation method cf. DeBruine, 2004. • Tiddeman, Stirrat & Perrett, 2005. Towards realism in facial transformation: results of a wavelet MRF method. Computer Graphics Forum, Eurographics conference issue, Vol 24, No 1-5. • DeBruine, 2004. Facial resemblance increases the attractiveness of same-sex face more than other-sex faces. Proc. R. Soc. Lond. B, 271:2085-2090. • Minear & Park, 2004.

  19. 2.2. Stimuli 50% Shape only transformation Player 2 Base face Player 2   50% 50% Shape of same-sex composite face Shape of subject’s face • DeBruine, 2004. • Tiddeman, Stirrat & Perrett, 2005. • Minear & Park, 2004.

  20. 2.3. Stimuli 50% Shape only transformation Player 2 Base face  50% Shape of same-sex composite face Shape of subject’s face • DeBruine, 2004. • Tiddeman , Stirratt & Perret, 2005. • Minear & Park, 2004.

  21. 2.3. Procedure • Trust game Player 2 subject

  22. 2.3. Procedure X 3! Player 2 subject Player 2 subject

  23. 2.3. Procedure Player 2 Subject Player 2 Subject

  24. Overview • Introduction & Predictions • Materials and Methods • Results • Discussion & Conclusions

  25. 3. Results

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  28. Overview • Introduction & Predictions • Materials and Methods • Results • Discussion & Conclusions • Female Subjects • Male Subjects

  29. 4. Discussion & Conclusions • The data seem to support the predictionthatextendedchilddependencyshapedcooperativebehaviour of relatedwomen. • They are consistent withother data (Essock-Vitale & McGuire, 1985). • Proximatemechanisms? • Essock-Vitale & McGuire, 1985.

  30. 4. Discussion & Conclusions • The data seem to be consistent with other data (Key & Aiello, 2000), suggesting that cooperative behavior of men towards women can evolve • When women face a relatively high cost of reproduction. • When there is a link between cooperation and reproduction, e.g. mating effort. • Other explanations? • Proximate mechanisms? • Key & Aiello, 2000. A Prisoner’s Dilemma Model of the Evolution of Paternal Care. Folia Primatologia, 71:77-92.

  31. Thankyou!

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