1 Psychology 305A: Personality Psychology September 30 Lecture 7

Psychology What are the basic principles of evolutionary theory? 2.How have the basic principles of evolutionary theory been adapted to the study of personality? The Biological Perspective 2

By the end of today’s class, you should be able to: 1. describe natural selection, sexual selection, intrasexual selection, and intersexual selection. 2. generate examples of distinct forms of selection define the terms reproductive capacity and minimal parental investment.

define the principle of divergence. 5. discuss the influence of birth order on the five dimensions of the five factor taxonomy. 4. relate sex differences in reproductive capacity and minimal parental investment to sex differences in mate preferences and desire for sexual variety.

Psychology 3055 What are the basic principles of evolutionary theory? Darwin proposed two processes through which evolution occurs: 5

Psychology Natural selection  A process through which organisms develop characteristics that enhance their ability to survive.  Organisms who possess characteristics that enhance their ability to survive are more likely to live to reproductive age and pass these characteristics on to the next generation. 6

Psychology 3057  Across successive generations, the “survival- enhancing” characteristics increase in frequency until they characterize most members of the species.  Offspring who inherit these characteristics are more likely to survive to reproductive age and pass the characteristics on to yet the next generation. 7

 Example: The preference for sweet, fatty, and salty foods among humans. 8

Psychology Sexual selection  A process through which organisms develop characteristics that enhance their ability to reproduce. 9  Darwin proposed two mechanisms through which sexual selection occurs:

Psychology (a) Intrasexual selection  Occurs when same sex organisms compete for the sexual interest of the opposite sex.  Organisms who possess characteristics that enable them to “win” the sexual interest of the opposite sex are more likely to mate and pass these characteristics on to the next generation. 10

Psychology  Offspring who inherit these characteristics are more likely to mate and pass the characteristics on to yet the next generation.  Across successive generations, the “winning” characteristics increase in frequency until they characterize most members of that sex of the species. 11

 Example: The aerial hover display of the male bronzed cowbird. 12

Psychology (b) Intersexual selection  Occurs when organisms of one sex prefer to mate with organisms of the opposite sex who possess specific, desirable characteristics.  Organisms who possess characteristics that are desirable to the opposite sex are more likely to mate and pass these characteristics on to the next generation. 13

Psychology  Offspring who inherit these characteristics are more likely to mate and pass the characteristics on to yet the next generation.  Across successive generations, the desirable characteristics increase in frequency until they characterize most members of that sex of the species. 14

 Example: The brilliant plumage of the male peacock. 15

Psychology How have the basic principles of evolutionary theory been adapted to the study of personality? Evolutionary psychologists believe that our psychological processes are the product of natural selection and sexual selection. Psychological processes are seen as adaptations to the survival and reproductive challenges faced by our ancestors. 16

17 With respect to personality, evolutionary psychologists have studied human universals (e.g., altruism), sex differences, and individual differences. The bulk of research has focused on sex differences and individual differences in personality. Examples:

Psychology Females and males differ in their reproductive capacity and the minimal parental investment that is required to produce an offspring:  Sex differences in personality

Psychology Reproductive capacity: Males > Females  Males: Can bear an almost unlimited number of offspring across the lifespan (maximum recorded to date: 900).  Females: Can bear 8 – 12 offspring across the lifespan. 19

Psychology Minimal parental investment: Females > Males  Females: Carry and nourish fetus for 9 months; nurse child after birth; during lactation, ovulation is suppressed.  Males: Engage in copulation. 20

21 Hypothesis A: Given sex differences in reproductive capacity and minimal parental investment, sex differences have evolved in mate preferences. Males value appearance in a mate more than females; females value resource potential in a mate more than males.

22 Evidence: Had participants rate several characteristics for their desirability in a potential mate: 0=irrelevant, 3= indispensable. Buss and Angleitner (1989; Buss et al., 2005; Li et al., 2011)

23 Pleasing disposition Sociability Neatness Mean Rating Male Female Dependability Good looks Good financial prospects Ambition and industriousness Good health

Psychology Alternative explanations for these findings? 24

25 Hypothesis B: Given sex differences in reproductive capacity and minimal parental investment, sex differences have evolved in desire for sexual variety. Males seek more sexual partners and are less discriminating in their choice of sexual partners than females.

Psychology Clark and Hatfield (1984; Schutzwohl et al., 2009) Had confederates approach students of the opposite sex on campus. After saying “Hi, I’ve been noticing you around campus lately and I find you very attractive,” the confederates asked the students 1 of 3 questions: 26 Evidence:

Psychology “Would you go out on a date with me tonight?” “Would you go back to my apartment with me tonight?” “Would you have sex with me tonight?” Percent Who Agreed Male Female

Psychology Buss and Schmitt (1993; Schmitt et al., 2003) Asked unmarried participants how many sex partners they would like to have through to the end of their lives. 28

Psychology Desired Number of Partners Time (Years) Life         Females          Males 29

Psychology Most animals, including humans, require some degree of parental investment in order to survive. When parents have more than one offspring, siblings must compete for parental investment. 30  Individual differences in personality First-born offspring (FBs) and later-born offspring (LBs) use different strategies to maximize parental investment.

Psychology Strategies used in non-human species:  Predatory birds confronted by a scarce food supply: Older chicks attempt to peck younger chicks to death or exclude them from the nest.  Cuckoo birds: First chick to hatch attempts to eject all other eggs from the nest. 31

Psychology Hypothesis A: FBs attempt to dominate younger siblings, resulting in higher levels of dominance and assertiveness (i.e., extraversion) among FBs. 32 Strategies used by humans:

Psychology Hypothesis B: LBs cooperate with older siblings to avoid physical confrontation, resulting in higher levels of cooperativeness and compliance (i.e., agreeableness) among LBs. Hypothesis C: FBs and LBs try to help their parents; however, FBs are asked for help more frequently than LBs, resulting in higher levels of dutifulness and responsibility (i.e., conscientiousness) among FBs. 33

Psychology  FBs > LBs in extraversion  FBs < LBs in agreeableness  FBs > LBs in conscientiousness 34 Evidence (see Sulloway, 1996):

By the end of today’s class, you should be able to: 1. describe natural selection, sexual selection, intrasexual selection, and intersexual selection. 2. generate examples of distinct forms of selection define the terms reproductive capacity and minimal parental investment.

36 6. define the principle of divergence. 5. discuss the influence of birth order on the five dimensions of the five factor taxonomy. 4. relate sex differences in reproductive capacity and minimal parental investment to sex differences in mate preferences and desire for sexual variety.