SV: Social psychology II: Relations
Chapter 1: evolutionary psychology
1. Altruism and natural selection: an evolutionary perspective on human
nature
1.1 Natural selection and behavior
• Evolutionary psychology investigates the evolutionary origin of behavior and
consequences for current psychological mechanisms.
• Darwin (1859): “The Origin of Species”
o Theory of natural selection: Selection in nature occurs because some
organisms survive better and reproduce better in a certain environment
▪ → survival of the fittest: better adaptation to environment
▪ → better fitness (= transferring next-generation genes)
• higher change to transfer your genes to the next generation
o Primary interest: evolution of physical features
• Modern Darwinians:
o Primary interest: evolution of behavior (e.g., altruistic behavior)
o Evolutionary perspective on human nature:
▪ Universal characteristics: These successful characteristics provide such an
evolutionary advantage, that they spread throughout the population and become
typical for all mankind
• Bipedalism (moving on two feet)
• Universal psychological features/characteristics
1
,1.2 Altruistic behavior
• Altruistic behavior = helping others although it may be detrimental to your own fitness
• ? <--> Natural selection = seemingly selfish process
• How to explain this?
o The universal need to belong
o Baumeister & Tyce (1990): “social anxiety” as an adaptation to prevent exclusion from the
group
▪ Being excluded from the group was the worst thing that could happen
▪ People that didn’t behave altruistically where excluded from the group and died
1.3 Inclusive fitness and kinship (= verwantschap) (Hamilton, 1964)
• = your personal reproductive success + the effects you have on the reproduction of your
genetic relatives, weighted by the degree of genetic relatedness
o identical twin: genetic relatedness = 100%
o parents - child: 50%
o brother/sister: 50%
o aunt/uncle - niece/nephew: 25%
o cousins: 12.5%
o → helping out related people also save a part of your own genes!
• Degree of genetic relatedness:
• = better fitness (of next generation) by helping (genetic) relatives
• This implies…
o One takes risks for genetic relatives
o The higher the genetic relatedness, the higher the risk one takes
▪ Daly & Wilson, 1988
• less care by step-parents than biological parents
• more child abuse by step-fathers (100 x more than biological fathers)
▪ Burnstein et al., 1994
• more help towards genetic relatives in trouble
2
,• The higher genetic related the higher change that
people will help (it is a bit more strong with life or
death)
• Here we see it is the young and the old ones: the
younger over the older ones because the younger
ones have higher reproductive changes
• U-shape
• Famine = hongersnood
o Inverted u-shape with a peak of the age of ten
o Children of the age of ten are not that far away from reproductive
age
o Better chance of survival than the baby’s
• Conclusion:
o Who we help in different situations is predictable from an
evolutionary perspective
o Strong evidence for the inclusive fitness theory
3
, 1.4 Reciprocal altruism (Trivers 1971)
• Why do we help unrelated individuals?
• “I help you when you help me” (bidirectional altruism)
o Only possible if
▪ the person being helped can be recognized later
▪ deceivers can be punished: cheaters are excluded
▪ → only in intelligent species (primates, humans)
▪ → only with acquaintances and small groups / tribes (guarantees reciprocity)
o In the end, helping increases fitness!
2. Sexual selection and sex differences in behavior: an evolutionary
perspective on sex differences
2.1 Sexual selection and parental investment
• Sexual selection = the selection of –and different access to– sexual partners
o Forms of sexual selection/competition:
▪ Intrasexual competition: the winner passes on more genes (male competition)
▪ Intersexual competition: choosing a mate based on their preferences (female choice)
o Parental investment theory (Trivers, 1972):
▪ Sexes differ in terms of time and effort spent in raising offspring (pregnancy, feeding,
protecting,…)
• Women invest more in raising offspring
→ variation in reproduction between the sexes
▪ female record: 69 children/ male record: over a 1000
→ this will result in several sex differences!
o Prediction: The sex that invests less in raising offspring will
prefer having more (sexual) partners
o Undergraduates – What’s the desired number of sexual
partners? (Buss & Schmitt, 1993)
▪ Women: 1 during the next month / 4 to 5 in their whole life
▪ Men: 2 during the next month / 8 during the next year / on
average 18 in their whole life
▪ Conclusion: men choose more partners
4
Chapter 1: evolutionary psychology
1. Altruism and natural selection: an evolutionary perspective on human
nature
1.1 Natural selection and behavior
• Evolutionary psychology investigates the evolutionary origin of behavior and
consequences for current psychological mechanisms.
• Darwin (1859): “The Origin of Species”
o Theory of natural selection: Selection in nature occurs because some
organisms survive better and reproduce better in a certain environment
▪ → survival of the fittest: better adaptation to environment
▪ → better fitness (= transferring next-generation genes)
• higher change to transfer your genes to the next generation
o Primary interest: evolution of physical features
• Modern Darwinians:
o Primary interest: evolution of behavior (e.g., altruistic behavior)
o Evolutionary perspective on human nature:
▪ Universal characteristics: These successful characteristics provide such an
evolutionary advantage, that they spread throughout the population and become
typical for all mankind
• Bipedalism (moving on two feet)
• Universal psychological features/characteristics
1
,1.2 Altruistic behavior
• Altruistic behavior = helping others although it may be detrimental to your own fitness
• ? <--> Natural selection = seemingly selfish process
• How to explain this?
o The universal need to belong
o Baumeister & Tyce (1990): “social anxiety” as an adaptation to prevent exclusion from the
group
▪ Being excluded from the group was the worst thing that could happen
▪ People that didn’t behave altruistically where excluded from the group and died
1.3 Inclusive fitness and kinship (= verwantschap) (Hamilton, 1964)
• = your personal reproductive success + the effects you have on the reproduction of your
genetic relatives, weighted by the degree of genetic relatedness
o identical twin: genetic relatedness = 100%
o parents - child: 50%
o brother/sister: 50%
o aunt/uncle - niece/nephew: 25%
o cousins: 12.5%
o → helping out related people also save a part of your own genes!
• Degree of genetic relatedness:
• = better fitness (of next generation) by helping (genetic) relatives
• This implies…
o One takes risks for genetic relatives
o The higher the genetic relatedness, the higher the risk one takes
▪ Daly & Wilson, 1988
• less care by step-parents than biological parents
• more child abuse by step-fathers (100 x more than biological fathers)
▪ Burnstein et al., 1994
• more help towards genetic relatives in trouble
2
,• The higher genetic related the higher change that
people will help (it is a bit more strong with life or
death)
• Here we see it is the young and the old ones: the
younger over the older ones because the younger
ones have higher reproductive changes
• U-shape
• Famine = hongersnood
o Inverted u-shape with a peak of the age of ten
o Children of the age of ten are not that far away from reproductive
age
o Better chance of survival than the baby’s
• Conclusion:
o Who we help in different situations is predictable from an
evolutionary perspective
o Strong evidence for the inclusive fitness theory
3
, 1.4 Reciprocal altruism (Trivers 1971)
• Why do we help unrelated individuals?
• “I help you when you help me” (bidirectional altruism)
o Only possible if
▪ the person being helped can be recognized later
▪ deceivers can be punished: cheaters are excluded
▪ → only in intelligent species (primates, humans)
▪ → only with acquaintances and small groups / tribes (guarantees reciprocity)
o In the end, helping increases fitness!
2. Sexual selection and sex differences in behavior: an evolutionary
perspective on sex differences
2.1 Sexual selection and parental investment
• Sexual selection = the selection of –and different access to– sexual partners
o Forms of sexual selection/competition:
▪ Intrasexual competition: the winner passes on more genes (male competition)
▪ Intersexual competition: choosing a mate based on their preferences (female choice)
o Parental investment theory (Trivers, 1972):
▪ Sexes differ in terms of time and effort spent in raising offspring (pregnancy, feeding,
protecting,…)
• Women invest more in raising offspring
→ variation in reproduction between the sexes
▪ female record: 69 children/ male record: over a 1000
→ this will result in several sex differences!
o Prediction: The sex that invests less in raising offspring will
prefer having more (sexual) partners
o Undergraduates – What’s the desired number of sexual
partners? (Buss & Schmitt, 1993)
▪ Women: 1 during the next month / 4 to 5 in their whole life
▪ Men: 2 during the next month / 8 during the next year / on
average 18 in their whole life
▪ Conclusion: men choose more partners
4
