Sociale psychologie II
SEM2 BA2
Juliet Scales
,1. Evolutionary psychology
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” (book)
→ 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 (= higher chance that your genes will be given to the next generation)
→ Primary interest: evolution of physical features vb. het lichaam van dieren verandert (vb. lange
nekken van giraffen) tot ze passen in hun omgeving
Modern Darwinians:
● Primary interest: evolution of behavior (e.g., altruistic behavior) (>< physical features)
● Evolutionary psychologists go back in time to search for explanations → universal
characteristics
● 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
⇒ vb. Bipedalism = humans started moving on two feet for evolutionary purposes
> they also go looking for: universal psychological features/characteristics
1.2. Altruistic behavior
How did humans become so social? Even though natural selection actually is quite selfish….
Altruistic behavior = helping others although it may be detrimental to your own fitness
><?
Natural selection = seemingly selfish process
How to explain this?: The universal need to belong
= people who didn’t behave altruistically, eventually died
Baumeister & Tyce: “social anxiety” as an adaptation, functional to prevent social exclusion
1.2.1 Inclusive fitness and kinship
= your personal reproductive success* + the effects you have on the reproduction of your genetic
relatives, weighted by the degree of genetic relatedness
*basically the number of children you have
• identical twin: genetic relatedness = 100%
• parents - child: 50%
• brother/sister: 50%
• aunt/uncle - niece/nephew: 25%
• cousins: 12.5%
> by helping out your own relatives, your own genes also are able to pass along, ergo; this is in your
advantage
= better fitness (of next generation) by helping (genetic) relatives
,This implies…
- One takes risks for genetic relatives
- The higher the genetic relatedness, the higher the risk one takes
Evidence:
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
Conclusion:
> Who we help in different situations is predictable from an evolutionary perspective
> Strong evidence for the inclusive fitness theory
> the higher genetically related you are, the more inclined you are to help them
> this is even more the case in life or death situations!
> you tend to help people who are in the most need of help (babies & elderly)
> in life or death situations people choose to save babies over elderly because of their
possibility to reproduce (evolutionary)
> famine conditions (longterm issue (>< life or death)): in this situation people choose the children
who are (almost) able to reproduce over babies
1.2.2 Reciprocal altruism (Trivers)
Why do we help unrelated individuals?
“I help you when you help me”
Reciprocal altruism = an organism temporarily sacrifices its own fitness to benefit another, with the
expectation that the favor will be returned later
Only possible if
1. the person being helped can be recognized later
2. deceivers can be punished (ex. excluded from future cooperation)
○ only possible in intelligent species (primates, humans)
○ only with acquaintances and small groups / tribes (guarantees reciprocity)
● In the end, helping increases fitness (ex. Receiving help from others in the future)
1.2. Sexual selection and parental investment
Sex: 2 categories: male and female (biological component counts) (≠ gender)
Sexual selection = the selection of –and different access to– sexual partners
Forms of sexual selection/competition:
● Intrasexual competition: the winner passes on more genes (male vs. male competition)
○ Ex. the reason why human penises are relatively massive
● Intersexual competition: choosing a mate based on their preferences (female choice)
Parental investment theory (Trivers, 1972):
, Sexes differ in terms of time and effort spent in raising offspring (pregnancy, feeding, protecting,…)
Core idea: Women invest more in raising offspring
⇒ variation in reproduction between the sexes: men can reproduce way more than women
female record: 69 children/ male record: over a 1000
⇒ this will result in several sex differences!
This raises several predictions:
Prediction 1: The sex that invests less in raising offspring will prefer having more (sexual)
partners
What’s the desired number of sexual partners?:
- Women: 1 in next month / 4 to 5 in their whole life
- Men: 2 in next month / 8 during the next year / on average 18 in their whole life
Conclusion:
> Men choose more partners: (d = .87) (!)
Prediction 2: The sex that invests less in raising offspring will be less selective in choosing
(sexual) partners
“I’ve noticed you around…I find you very attractive” experiment:
● Would you go out with me tonight? (F: 55% / M: 50%)
● Would you come over to my apartment tonight? (F: 6% / M: 69%)
● Would you go to bed with me tonight? (F: 0% / M: 75%)
> very big sex difference!
Replication studies ~ identical findings
Conclusion:
> Attitude towards casual sex: men more positive
• Oliver & Hyde: d = .81
• Petersen & Hyde: d = .45
Probability of consenting to sexual intercourse after
having known someone for a certain time
-3 = definitely not
0 = neutral
3 = definitely yes
Women: highly unlikely to have sex after knowing
someone for 1 week
Conclusion:
> Men are less selective in choosing sexual partners
1.3. Mating preferences
Prediction:
● What do men and women find most important in a potential partner?:
○ Men: youth and physically attractiveness (~ sign of fertility)
○ Women: financial support (good financial prospect)
⇒ Confirmed in 37 cultures
SEM2 BA2
Juliet Scales
,1. Evolutionary psychology
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” (book)
→ 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 (= higher chance that your genes will be given to the next generation)
→ Primary interest: evolution of physical features vb. het lichaam van dieren verandert (vb. lange
nekken van giraffen) tot ze passen in hun omgeving
Modern Darwinians:
● Primary interest: evolution of behavior (e.g., altruistic behavior) (>< physical features)
● Evolutionary psychologists go back in time to search for explanations → universal
characteristics
● 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
⇒ vb. Bipedalism = humans started moving on two feet for evolutionary purposes
> they also go looking for: universal psychological features/characteristics
1.2. Altruistic behavior
How did humans become so social? Even though natural selection actually is quite selfish….
Altruistic behavior = helping others although it may be detrimental to your own fitness
><?
Natural selection = seemingly selfish process
How to explain this?: The universal need to belong
= people who didn’t behave altruistically, eventually died
Baumeister & Tyce: “social anxiety” as an adaptation, functional to prevent social exclusion
1.2.1 Inclusive fitness and kinship
= your personal reproductive success* + the effects you have on the reproduction of your genetic
relatives, weighted by the degree of genetic relatedness
*basically the number of children you have
• identical twin: genetic relatedness = 100%
• parents - child: 50%
• brother/sister: 50%
• aunt/uncle - niece/nephew: 25%
• cousins: 12.5%
> by helping out your own relatives, your own genes also are able to pass along, ergo; this is in your
advantage
= better fitness (of next generation) by helping (genetic) relatives
,This implies…
- One takes risks for genetic relatives
- The higher the genetic relatedness, the higher the risk one takes
Evidence:
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
Conclusion:
> Who we help in different situations is predictable from an evolutionary perspective
> Strong evidence for the inclusive fitness theory
> the higher genetically related you are, the more inclined you are to help them
> this is even more the case in life or death situations!
> you tend to help people who are in the most need of help (babies & elderly)
> in life or death situations people choose to save babies over elderly because of their
possibility to reproduce (evolutionary)
> famine conditions (longterm issue (>< life or death)): in this situation people choose the children
who are (almost) able to reproduce over babies
1.2.2 Reciprocal altruism (Trivers)
Why do we help unrelated individuals?
“I help you when you help me”
Reciprocal altruism = an organism temporarily sacrifices its own fitness to benefit another, with the
expectation that the favor will be returned later
Only possible if
1. the person being helped can be recognized later
2. deceivers can be punished (ex. excluded from future cooperation)
○ only possible in intelligent species (primates, humans)
○ only with acquaintances and small groups / tribes (guarantees reciprocity)
● In the end, helping increases fitness (ex. Receiving help from others in the future)
1.2. Sexual selection and parental investment
Sex: 2 categories: male and female (biological component counts) (≠ gender)
Sexual selection = the selection of –and different access to– sexual partners
Forms of sexual selection/competition:
● Intrasexual competition: the winner passes on more genes (male vs. male competition)
○ Ex. the reason why human penises are relatively massive
● Intersexual competition: choosing a mate based on their preferences (female choice)
Parental investment theory (Trivers, 1972):
, Sexes differ in terms of time and effort spent in raising offspring (pregnancy, feeding, protecting,…)
Core idea: Women invest more in raising offspring
⇒ variation in reproduction between the sexes: men can reproduce way more than women
female record: 69 children/ male record: over a 1000
⇒ this will result in several sex differences!
This raises several predictions:
Prediction 1: The sex that invests less in raising offspring will prefer having more (sexual)
partners
What’s the desired number of sexual partners?:
- Women: 1 in next month / 4 to 5 in their whole life
- Men: 2 in next month / 8 during the next year / on average 18 in their whole life
Conclusion:
> Men choose more partners: (d = .87) (!)
Prediction 2: The sex that invests less in raising offspring will be less selective in choosing
(sexual) partners
“I’ve noticed you around…I find you very attractive” experiment:
● Would you go out with me tonight? (F: 55% / M: 50%)
● Would you come over to my apartment tonight? (F: 6% / M: 69%)
● Would you go to bed with me tonight? (F: 0% / M: 75%)
> very big sex difference!
Replication studies ~ identical findings
Conclusion:
> Attitude towards casual sex: men more positive
• Oliver & Hyde: d = .81
• Petersen & Hyde: d = .45
Probability of consenting to sexual intercourse after
having known someone for a certain time
-3 = definitely not
0 = neutral
3 = definitely yes
Women: highly unlikely to have sex after knowing
someone for 1 week
Conclusion:
> Men are less selective in choosing sexual partners
1.3. Mating preferences
Prediction:
● What do men and women find most important in a potential partner?:
○ Men: youth and physically attractiveness (~ sign of fertility)
○ Women: financial support (good financial prospect)
⇒ Confirmed in 37 cultures
