Jessica Reyes M 2024-2025
Social psychology 2: relations
HT- 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.
He is the first one to make the theory.
Darwin (1859): “The Origin of Species”
Theory of natural selection: Selection in nature occurs because some organisms
survive better and reproduce better in a certain environment
o survival of the fittest: better adaptation to environment
o better fitness (= transferring next-generation genes)
Primary interest: evolution of physical features
The idea: selection happens because the organism is going to survive according to
how they can adapt and reproduce themselves.
Came over dispute bc people believed in God and their creations (this was
kind of controversial)
Example of giraffe: in Africa you have dry, long trees. Where only the long giraffes
could reach those leaves, and this was crucial for their survival. long neck survived
and those w short neck would die out of hunger
Modern Darwinians:
o Primary interest: evolution of behavior (e.g., altruistic behavior) going way back in
time
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. became the norm
o Bipedalism walks in 2 feet (has so many perks)
o Universal psychological features/characteristics such as….
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?
The universal need to belong Baumeister & Tyce (1990): “social anxiety” as an adaptation to prevent
exclusion from the group
1
, Jessica Reyes M 2024-2025
Because it sits in our DNA, we act how we act for the need of belonging. Imagine you did not try to
help or to have this behaviour, you would get excluded. we act this way then as a form of
prevention of getting excluded.
Look at anxiety the fear of getting excluded, or getting negatively judged.
1.3 Inclusive fitness and kinship
= your personal reproductive success (ur own kids) + the affects you have on the reproduction of your
genetic relatives, weighted by the degree of genetic relatedness
- identical twin: genetic relatedness = - brother/sister: 50%
100% - aunt/uncle - niece/nephew: 25%
- parents - child: 50% - cousins: 12.5%
By saving ur own kind (family member) you save ur own bloodline. I pass them along
Degree of genetic relatedness:
= 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
o Daly & Wilson, 1988
less care by stepparents than biological parents because it isn’t mine
more child abuse by stepfathers (100 x more than biological fathers)
o Burnstein et al., 1994
more help towards genetic relatives in trouble
he tested the fitness theory, who would u help in this case. For example,
house on fire:
age related: we help those that are young and very old
in everyday situations we help less the highly related age, AKA the U-shaped curve. everyday help
people, but in life death, we help more our high But for life or death, we help the younger people who want
related people. still to reproduce and make children.
2
,Jessica Reyes M 2024-2025
Conclusion:
Who we help in different situations is predictable from an evolutionary
perspective
Convincing evidence for the inclusive fitness theory
Under famine conditions (people starving out of hunger) we invert the U- curved
shape.
We see a peak into helping children 10 YO: because their reproductive
organism is more nearby than the babies. However, babies need a lot,
compared to the difficult environment where they are. So, we just give
them up.
1.4 Reciprocal altruism
Why do we help unrelated individuals? “I help you when you help me”
Only 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)
In the end, helping increases fitness!
2. Sexual Selection and Sex Differences in Behavior: An evolutionary
perspective on sex differences
2.1Sexual selection and parental investment
Sexual selection = the selection of –and different access to– sexual partners
- Forms of sexual selection/competition:
o Intrasexual competition: the winner passes on more genes (male competition)
o 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,)
- women invest more in raising offspring
- variation in reproduction between the sexes
o female record: 69 children/ male record: over a 1000
this will result in several sex differences!
Prediction: The sex that invests less in raising offspring will prefer having
more (sexual) partners
- Undergraduates – What’s the desired number of sexual partners?
(Buss & Schmitt, 1993)
o Women: 1 during the next month / 4 to 5 in their whole life
o Men: 2 during the next month / 8 during the next year / on
average 18 in their whole life
3
, Jessica Reyes M 2024-2025
Prediction: The sex that invests less in raising offspring will
be less selective in choosing (sexual) partners
- Undergraduates – “I’ve noticed you around…I find
you very attractive”: (Clark & Hatfield, 1989)
o Would you go out with me tonight? (F: 55% / M: 50%)
o Would you come over to my apartment tonight? (F: 6% / M: 69%)
o Would you go to bed with me tonight? (F: 0% / M: 75%)
- Replication in Austria ~ identical findings (Voracek et al., 2005)
- Attitude towards casual sex: men more positive
o Oliver & Hyde (1993): d = .81
o Petersen & Hyde (2010): d = .45
Probability of consenting to sexual intercourse after having known someone for a certain time (Buss &
Schmitt, 1993)
-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
2.2Mating preferences
Prediction:
Men are looking for partner who is young and physically attractive (~ sign of fertility)
Women are looking for a partner who can provide financial support (good financial prospect)
- Confirmed in 37 cultures (Buss, 1989); Replicated (Walter et al., 2020)
Structural powerlessness hypothesis:
Alternative explanation for the difference / Eagly & Wood (1999): men are associated with the role of
breadwinner / ‘money maker’; women are financially dependent on their man (gender roles)
↔ When women have a higher income/SES (“money is not an issue”), they place even higher
importance to financial means/SES in men (Buss, 1989; Delton et al., 2006; Todosijevic et al., 2003;
Wiederman & Allgeier, 1992)
Buss (1989): 10,047 respondents in 37 cultures:
- women long for a partner who provides - men long for a partner who is younger
financial perspectives - men long for a partner who is physically
- women long for a partner who is attractive
ambitious and industrious
- women long for a partner who is older
Walter et al. (2020):
- Replication study using a new 45-country sample (N = 14,399)
4
Social psychology 2: relations
HT- 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.
He is the first one to make the theory.
Darwin (1859): “The Origin of Species”
Theory of natural selection: Selection in nature occurs because some organisms
survive better and reproduce better in a certain environment
o survival of the fittest: better adaptation to environment
o better fitness (= transferring next-generation genes)
Primary interest: evolution of physical features
The idea: selection happens because the organism is going to survive according to
how they can adapt and reproduce themselves.
Came over dispute bc people believed in God and their creations (this was
kind of controversial)
Example of giraffe: in Africa you have dry, long trees. Where only the long giraffes
could reach those leaves, and this was crucial for their survival. long neck survived
and those w short neck would die out of hunger
Modern Darwinians:
o Primary interest: evolution of behavior (e.g., altruistic behavior) going way back in
time
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. became the norm
o Bipedalism walks in 2 feet (has so many perks)
o Universal psychological features/characteristics such as….
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?
The universal need to belong Baumeister & Tyce (1990): “social anxiety” as an adaptation to prevent
exclusion from the group
1
, Jessica Reyes M 2024-2025
Because it sits in our DNA, we act how we act for the need of belonging. Imagine you did not try to
help or to have this behaviour, you would get excluded. we act this way then as a form of
prevention of getting excluded.
Look at anxiety the fear of getting excluded, or getting negatively judged.
1.3 Inclusive fitness and kinship
= your personal reproductive success (ur own kids) + the affects you have on the reproduction of your
genetic relatives, weighted by the degree of genetic relatedness
- identical twin: genetic relatedness = - brother/sister: 50%
100% - aunt/uncle - niece/nephew: 25%
- parents - child: 50% - cousins: 12.5%
By saving ur own kind (family member) you save ur own bloodline. I pass them along
Degree of genetic relatedness:
= 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
o Daly & Wilson, 1988
less care by stepparents than biological parents because it isn’t mine
more child abuse by stepfathers (100 x more than biological fathers)
o Burnstein et al., 1994
more help towards genetic relatives in trouble
he tested the fitness theory, who would u help in this case. For example,
house on fire:
age related: we help those that are young and very old
in everyday situations we help less the highly related age, AKA the U-shaped curve. everyday help
people, but in life death, we help more our high But for life or death, we help the younger people who want
related people. still to reproduce and make children.
2
,Jessica Reyes M 2024-2025
Conclusion:
Who we help in different situations is predictable from an evolutionary
perspective
Convincing evidence for the inclusive fitness theory
Under famine conditions (people starving out of hunger) we invert the U- curved
shape.
We see a peak into helping children 10 YO: because their reproductive
organism is more nearby than the babies. However, babies need a lot,
compared to the difficult environment where they are. So, we just give
them up.
1.4 Reciprocal altruism
Why do we help unrelated individuals? “I help you when you help me”
Only 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)
In the end, helping increases fitness!
2. Sexual Selection and Sex Differences in Behavior: An evolutionary
perspective on sex differences
2.1Sexual selection and parental investment
Sexual selection = the selection of –and different access to– sexual partners
- Forms of sexual selection/competition:
o Intrasexual competition: the winner passes on more genes (male competition)
o 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,)
- women invest more in raising offspring
- variation in reproduction between the sexes
o female record: 69 children/ male record: over a 1000
this will result in several sex differences!
Prediction: The sex that invests less in raising offspring will prefer having
more (sexual) partners
- Undergraduates – What’s the desired number of sexual partners?
(Buss & Schmitt, 1993)
o Women: 1 during the next month / 4 to 5 in their whole life
o Men: 2 during the next month / 8 during the next year / on
average 18 in their whole life
3
, Jessica Reyes M 2024-2025
Prediction: The sex that invests less in raising offspring will
be less selective in choosing (sexual) partners
- Undergraduates – “I’ve noticed you around…I find
you very attractive”: (Clark & Hatfield, 1989)
o Would you go out with me tonight? (F: 55% / M: 50%)
o Would you come over to my apartment tonight? (F: 6% / M: 69%)
o Would you go to bed with me tonight? (F: 0% / M: 75%)
- Replication in Austria ~ identical findings (Voracek et al., 2005)
- Attitude towards casual sex: men more positive
o Oliver & Hyde (1993): d = .81
o Petersen & Hyde (2010): d = .45
Probability of consenting to sexual intercourse after having known someone for a certain time (Buss &
Schmitt, 1993)
-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
2.2Mating preferences
Prediction:
Men are looking for partner who is young and physically attractive (~ sign of fertility)
Women are looking for a partner who can provide financial support (good financial prospect)
- Confirmed in 37 cultures (Buss, 1989); Replicated (Walter et al., 2020)
Structural powerlessness hypothesis:
Alternative explanation for the difference / Eagly & Wood (1999): men are associated with the role of
breadwinner / ‘money maker’; women are financially dependent on their man (gender roles)
↔ When women have a higher income/SES (“money is not an issue”), they place even higher
importance to financial means/SES in men (Buss, 1989; Delton et al., 2006; Todosijevic et al., 2003;
Wiederman & Allgeier, 1992)
Buss (1989): 10,047 respondents in 37 cultures:
- women long for a partner who provides - men long for a partner who is younger
financial perspectives - men long for a partner who is physically
- women long for a partner who is attractive
ambitious and industrious
- women long for a partner who is older
Walter et al. (2020):
- Replication study using a new 45-country sample (N = 14,399)
4
