Evolutionary Forces on Evolutionary Forces on personalitypersonalitySociobiology = the study of biological bases of Sociobiology = the study of biological bases of

social behaviorsocial behavior**psychological qualities have been retained in **psychological qualities have been retained in people over many years because they are people over many years because they are adaptiveadaptive

3 important points:3 important points:1.1. Reproductive successReproductive success2.2. Adaptive value pertains to early life Adaptive value pertains to early life 3.3. Adaptive value in terms of specific tasks in specific Adaptive value in terms of specific tasks in specific

situationssituations

What psychological What psychological mechanisms have evolved?mechanisms have evolved?

Male/female mate preferencesMale/female mate preferences• Females will have stronger preferencesFemales will have stronger preferences• Females focus on mates’ ability to Females focus on mates’ ability to

provide resourcesprovide resources• Males focus on reproductive potentialMales focus on reproductive potential

Sex objects vs. success objectsSex objects vs. success objects

Evolutionary theory and attractionEvolutionary theory and attraction  Genetic similarity theoryGenetic similarity theory (Rushton, 1989; Rushton, Russell & Wells, (Rushton, 1989; Rushton, Russell & Wells,

1984):1984):• more attracted to strangers who resemble you than who more attracted to strangers who resemble you than who

don’tdon’t• leads to offspring with not only your genes but genes like leads to offspring with not only your genes but genes like

themselvesthemselves• Rushton’s research shows that people are more attracted to Rushton’s research shows that people are more attracted to

genetically similar peoplegenetically similar people• People who go on to have children together are more alike People who go on to have children together are more alike

than those who don’t. Thus among sexually active couples, than those who don’t. Thus among sexually active couples, those most genetically similar are those most likely to have those most genetically similar are those most likely to have reproduced.reproduced.

• Attraction not limited to the opposite sex. We tend to be Attraction not limited to the opposite sex. We tend to be friends with people who are genetically similar. Why? From friends with people who are genetically similar. Why? From an evolutionary perspective it’s because you are more likely an evolutionary perspective it’s because you are more likely to be altruistic to a friend than a stranger, making it more to be altruistic to a friend than a stranger, making it more likely that the friend will go onto reproduce (similar genes to likely that the friend will go onto reproduce (similar genes to your own) and you may n\meet the friend’s opposite sex your own) and you may n\meet the friend’s opposite sex sibling - close genes again!sibling - close genes again!

• How do we detect this genetic similarity: either drawn to How do we detect this genetic similarity: either drawn to those with similar facial and bodily features OR via smell.those with similar facial and bodily features OR via smell.

Please think of a serious committed relationshipPlease think of a serious committed relationshipyou have had in the past, that you currently have,you have had in the past, that you currently have,or that you would like to have. Imagine that theor that you would like to have. Imagine that theperson with whom you’ve become seriouslyperson with whom you’ve become seriouslyinvolved became interested in someone else. involved became interested in someone else.

WhatWhatwould distress or upset you more?would distress or upset you more?

– (a) Imagining your partner forming a deep emotional (a) Imagining your partner forming a deep emotional attachment to that person ORattachment to that person OR

– (b) Imagining your partner enjoying passionate (b) Imagining your partner enjoying passionate sexual intercourse with that personsexual intercourse with that person

Sexual/relationship jealousySexual/relationship jealousy

Based on evolutionary forces, men and women Based on evolutionary forces, men and women approachapproach

sexual jealousy differentlysexual jealousy differently

Buss, Larsen, Westen, and Semmelroth (1992) men andBuss, Larsen, Westen, and Semmelroth (1992) men andwomen were asked to respond to the previous vignette:women were asked to respond to the previous vignette:  

FEMALES = 82% option (a) 18% option (b)FEMALES = 82% option (a) 18% option (b)MALES = 40% option (a); 60% option (b)MALES = 40% option (a); 60% option (b)

Males jealous of sexual fidelityMales jealous of sexual fidelityFemales jealous of emotional fidelityFemales jealous of emotional fidelity

Brain function and Brain function and personalitypersonality1.1. Behavioral approach system (BAS)Behavioral approach system (BAS)

• IncentivesIncentives• Left frontal lobeLeft frontal lobe• dopaminedopamine

2.2. Behavioral inhibition system (BIS)Behavioral inhibition system (BIS)• withdrawalwithdrawal• Right frontal lobeRight frontal lobe• Serotonin?Serotonin?• Anxiety/cues of threatAnxiety/cues of threat

BAS and BIS act independentlyBAS and BIS act independently

Link to temperamentLink to temperament

1.1. BIS sensitivity and emotional BIS sensitivity and emotional instability/neuroticisminstability/neuroticism

2.2. BAS sensitivity related to BAS sensitivity related to extraversionextraversion

3.3. Role of impulsivityRole of impulsivity

4.4. Zuckerman – sensation seekingZuckerman – sensation seeking

Role of hormonesRole of hormones

Sex hormones important:Sex hormones important:•weeks 8 – 24 prenatally, in months 1-5 after weeks 8 – 24 prenatally, in months 1-5 after

birth, and after pubertybirth, and after puberty

•changes to nervous systemchanges to nervous system

Link to behavior in childrenLink to behavior in childrenReinisch, 1981Reinisch, 1981

sex differencesex differenceeffect of prenatal exposureeffect of prenatal exposurefilter by cognitionsfilter by cognitions

Hormonal links to behavior in Hormonal links to behavior in children continuedchildren continued

Berenbaum & Hines (1992)Berenbaum & Hines (1992)1.1. Androgen exposed girls played with Androgen exposed girls played with

boys’ toysboys’ toys2.2. No difference in boysNo difference in boys

Jacklin, Maccoby, & Doering (1983)Jacklin, Maccoby, & Doering (1983)1.1. Boldness or timidity of infant boysBoldness or timidity of infant boys2.2. No effect for girlsNo effect for girls

• Testosterone and adult personalityTestosterone and adult personality