sex differences in nepotism trust in a trust game is associated with sex, exposure to baby’s and...
TRANSCRIPT
Sex differences in Sex differences in nepotismnepotism
Trust in a trust game is associated with sex, Trust in a trust game is associated with sex, exposure to baby’s and facial similarityexposure to baby’s and facial similarity
Katinka Quintelier, Ghent [email protected]
www.themoralbrain.be
June 5, 2008HBES 2008, Kyoto
1 Introduction
The fossil record of the genus The fossil record of the genus HomoHomo (Wood & (Wood & Collard, 1999) versus earlier hominins suggests:Collard, 1999) versus earlier hominins suggests:
Slower maturation, prolonged development of children
Increase in brain size
Obligate bipedalism
Increase in body size
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
1 Introduction
What also evolved since the emergence of the genus What also evolved since the emergence of the genus HomoHomo::
Shorter lactation period & interbirth interval (Aiello & Key, 2002)
Very long dependency of children
Raising several dependent children simultaneously 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.
1. Introduction
Who would assist a mother to decrease the burden of child care? Who would assist a mother to decrease the burden of child care?
C < rB (Hamilton, 1964)C < rB (Hamilton, 1964)
Father Father paternal care paternal care
Kin Kin cooperative breeding cooperative breeding
““Cooperative breeding is a breeding system in which group Cooperative breeding is a breeding system in which group members, other than the genetic parents (alloparents), help one members, other than the genetic parents (alloparents), help one or both parents rear their offspring”.or both parents rear their offspring”.
Hrdy, 2005.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.
•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.
1. Introduction
Mother Maternal
grandmothers Paternal
grandmothers Older siblings
Sear and Mace, 2008.
1. Introduction
Women are expected to be more nepotistic than men. Reproductive Women are expected to be more nepotistic than men. Reproductive succes can be increased by :succes can be increased by :
Increasing survival of offspring (getting help from kin)Increasing survival of offspring (getting help from kin) Increasing inclusive fitness (helping kin)Increasing inclusive fitness (helping kin) Increasing quantity of offspringIncreasing quantity of offspring
Some data support this hypothesis.Some data support this hypothesis.
(LA) Women give more help to and receive more help from wealthy female kin with (LA) Women give more help to and receive more help from wealthy female kin with children. (Essock-Vitale & McGuire, 1985)children. (Essock-Vitale & McGuire, 1985)
(Canadian) Sisters recalled more relatives and refered more to kinship status in (Canadian) Sisters recalled more relatives and refered more to kinship status in characterizing themselves, than their brothers did. (Salmon & Daly, 1996)characterizing themselves, than their brothers did. (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.
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.
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.
Overview
1. Introduction & Predictions
2. Materials and Methods
1. Design2. Participants3. Stimuli4. Procedure
3. Results
4. Discussion & Conclusions
2.1. Design2.1. Design
Subject’s sexSubject’s sex 2 conditions2 conditions
Picture evaluation taskPicture evaluation task 2 conditions: landscape or baby2 conditions: landscape or baby
Trust gameTrust game 2 conditions: resemblance or no resemblance2 conditions: resemblance or no resemblance « Player 2 » was always female!« Player 2 » was always female!
2 x 2 x 2, all between subjects variables2 x 2 x 2, all between subjects variables
The entire program ran in «Presentation 12.1.»The entire program ran in «Presentation 12.1.»
2.1. Design2.1. Design
Subject’s sexSubject’s sex 2 conditions2 conditions
Picture evaluation taskPicture evaluation task 2 conditions: landscape or baby2 conditions: landscape or baby
Trust gameTrust game 2 conditions: resemblance or no resemblance2 conditions: resemblance or no resemblance « Player 2 » was always female!« Player 2 » was always female!
2 x 2 x 2, all between subjects variables2 x 2 x 2, all between subjects variables
The entire program ran in «Presentation 12.1 »The entire program ran in «Presentation 12.1 »
2.1. Design2.1. Design
Subject’s sexSubject’s sex 2 conditions2 conditions
Picture evaluation taskPicture evaluation task 2 conditions: landscape or baby2 conditions: landscape or baby
Trust gameTrust game 2 conditions: resemblance or no resemblance2 conditions: resemblance or no resemblance « Player 2 » was always female!« Player 2 » was always female!
2 x 2 x 2, all between subjects variables2 x 2 x 2, all between subjects variables
The entire program ran in «Presentation 12.1 »The entire program ran in «Presentation 12.1 »
2.2. Stimuli
Trust game
Two conditions
Condition 1: player 2 resembles participant
Condition 2: player 2 does not resemble participant
Player 2 Base face
•Minear & Park, 2004. A lifespan database of adult facial stimuli. Behavior Research Methods, Instruments, & Computers, 36 (4):630-633.
2.2. Stimuli
Facial Stimuli Database
http://agingmind.utdallas.edu/
Player 2 Base face
2.2. Stimuli
•Image manipulation software: Psychomorph (Tiddeman et al., 2005)
•Transformation method cf. DeBruine, 2004.
50% Shape only transformation
Player 2
• 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.
Subject
•DeBruine, 2004. •Tiddeman, Stirrat & Perrett, 2005.•Minear & Park, 2004.
50%
50% Shape only transformation
Player 2 Base face
Shape of subject’s face
Shape ofsame-sex composite face
2.2. Stimuli
Player 2
50%
Player 2 Base face
• DeBruine, 2004.•Tiddeman , Stirratt & Perret, 2005.•Minear & Park, 2004.
2.3. Stimuli
50%
Shape of subject’s face
Shape ofsame-sex composite face
50% Shape only transformation
3. Results
Source Type III Sum of Squares df Mean Square F Sig.
Corrected Model 40.282(a) 7 5.755 2.386 .029 Intercept 1315.307 1 1315.307 545.355 .000 sex 5.079 1 5.079 2.106 .151 contextual_cue 12.061 1 12.061 5.001 .028 similarity 7.111 1 7.111 2.948 .090 sex * contextual_cue 2.095 1 2.095 .868 .354 sex * similarity 1.954 1 1.954 .810 .371 contextual_cue * similarity .821 1 .821 .340 .561 sex * contextual_cue * similarity 10.621 1 10.621 4.404 .039
Error 195.359 81 2.412 Total 1573.000 89 Corrected Total 235.640 88
Overview
1. Introduction & Predictions
2. Materials and Methods
3. Results
4. Discussion & Conclusions
1. Female Subjects2. Male Subjects
4. Discussion & Conclusions
The data seem to support the prediction that extended child dependency shaped cooperative behaviour of related women.
They are consistent with other data (Essock-Vitale & McGuire, 1985).
Proximate mechanisms?
•Essock-Vitale & McGuire, 1985.
4. Discussion & Conclusions
•Key & Aiello, 2000. A Prisoner’s Dilemma Model of the Evolution of Paternal Care. Folia Primatologia, 71:77-92.
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?