1 Psychology 305A: Personality Psychology October 1 Lecture 7

ASTU 400U Disordered Eating – Biology and Behaviour How Does it Work? A student-led seminar (12-15 participants) We explore and teach each other the course material as a group What Are We Learning About? The characteristics, underlying mechanisms, and treatment of disordered eating! Topics ranging from obesity and food addiction, to bulimia nervosa and anorexia nervosa Special focus on clinical and biological approaches Interested? Jacob Sussman (course coordinator) for more information about the course and for answers to any questions you might Check out the SDS website:

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? 3. What hypotheses has the evolutionary approach generated regarding (a) altruism and (b) sex differences in the desire for sexual variety? The Biological Perspective 3

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 term inclusive fitness. 4. review research supporting evolutionary hypotheses related to altruism. 4

5 5. define the terms reproductive capacity and minimal parental investment. 6. review research supporting evolutionary hypotheses related to sex differences in the desire for sexual variety. 5

Psychology 3056 What are the basic principles of evolutionary theory? Darwin proposed two processes through which evolution occurs: 6

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. 7

Psychology 3058  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. 8

 Example: The preference for sweet, fatty, and salty foods among humans. 9

Psychology Sexual selection  A process through which organisms develop characteristics that enhance their ability to reproduce. 10  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. 11

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. 12

 Example: The aerial hover display of the male bronzed cowbird. 13

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. 14

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. 15

 Example: The brilliant plumage of the male peacock. 16

Psychology How have the basic principles of evolutionary theory been adapted to the study of personality? Evolutionary psychologists believe that our basic psychological processes are the product of natural selection and sexual selection. Our psychological processes are seen as adaptations to the survival and reproductive challenges faced by our ancestors. 17

Psychology What hypotheses has the evolutionary approach generated regarding altruism? Altruism: A desire to help others, often at the risk of one’s own well-being. Theory of inclusive fitness: Organisms are motivated to enhance the survival and reproductive potential of those who are genetically similar to them. 18

Psychology Following from the theory of inclusive fitness, evolutionary psychologists generated two hypotheses:  Hypothesis B: Helping behaviour increases as the reproductive potential of one’s kin member (i.e., relative) increases.  Hypothesis A: Helping behaviour increases as the degree of genetic overlap increases between the helper and the recipient. 19

Psychology Burnstein et al. (1994; also see Laham et al., 2005):  Had participants imagine that people were asleep in a rapidly burning building.  Told participants they could only rescue one person.  Asked participants to indicate who they would be most willing to save. 20  Recruited American and Japanese participants.

Psychology Tendency to Help Degree of Genetic Overlap Highly Related Not Related      Results consistent with Hypothesis A. 21

Psychology Tendency to Help Age of Kin (Years)       Results consistent with Hypothesis B. 22

Psychology Tendency to Help Degree of Genetic Overlap Highly Related Not Highly Related     Results consistent with Hypothesis B.    Healthy Sick 23

Psychology What hypotheses has the evolutionary approach generated regarding sex differences in the desire for sexual variety? Females and males differ in their reproductive capacity and the minimal parental investment that is required to produce an offspring: 24

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. 25

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. 26

Psychology Given sex differences in reproductive capacity and minimal parental investment, evolutionary psychologists maintain that males and females have developed different strategies to maximize their reproductive potential: 27

Psychology Males: Employ strategies that enable them to copulate with as many females as possible. Females: Employ strategies that restrict copulation to males who are able to provide care and resources for the offspring. 28

Psychology Following from these strategies, evolutionary psychologists generated two hypotheses:  Hypothesis A: Males are less discriminating in their selection of sexual partners than females.  Hypothesis B: Males are inclined to seek more sexual partners than females. 29

Psychology Studies that have tested these hypotheses include:  Clark and Hatfield (1984)  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: 30

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)  Asked unmarried participants how many sex partners they would like to have through to the end of their lives. 32

Psychology Desired Number of Partners Time (Years) Life         Females          Males  Results consistent with Hypothesis B. 33

Psychology  Schmitt et al. (2003): Found similar sex differences across 52 nations (e.g., Argentina, Austria, Canada, Chile, Croatia, Greece, Israel, Italy, Japan, Lebanon, Slovakia, Zimbabwe, US). 34

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 term inclusive fitness. 4. review research supporting evolutionary hypotheses related to altruism. 35

36 5. define the terms reproductive capacity and minimal parental investment. 6. review research supporting evolutionary hypotheses related to sex differences in the desire for sexual variety. 36