Psychology 305B: Theories of Personality Lecture 5

1. Psychology 305B: Theories of Personality Lecture 5 Psychology 305

2. Announcements • Please note that the grades for the first exam are now posted on the course website. The mean score on the exam was 70% (SD=18%). • The Registrar’s Office has schedule the date of the second exam: December 17th, at 7:00 PM. Psychology 305

3. Lecture 5 Questions That Will be Answered in Today’s Lecture • Biological Perspective on Personality: Evolutionary Approach • What are the basic principles of evolutionary theory and how have they been adapted to the study of personality? • What hypotheses has the evolutionary approach generated regarding (a) altruism, (b) sex differences in the desire for sexual variety, (c) sex differences in jealousy and (d) birth order and personality? Psychology 305

4. What are the basic principles of evolutionary theory and how have they been adapted to the study of personality? • According to Darwin’s theory of evolution, across successive generations of a species, organisms develop characteristics that enhance their ability to survive and reproduce. • Darwin maintained that there are two processes through which organisms develop these characteristics: Psychology 305

5. 1. Natural Selection • A process through which organisms develop characteristics that enhance their ability to survive. • Organisms that possess characteristics that enhance their ability to survive are more likely to live to reproductive age and to pass these characteristics on to the next generation. • Offspring that inherit these characteristics, in turn, are more likely to live to reproductive age and to pass the characteristics on to yet the next generation. Psychology 305

6. Through this process, characteristics that enhance the organism’s ability to survive increase in frequency across successive generations of the species until they come to characterize virtually all members of the species. • E.g. of a characteristic that has evolved through natural selection : The preference for sweet, fatty, and salty foods in humans. Psychology 305

7. 2. Sexual Selection • A process through which organisms develop characteristics that enhance their ability to reproduce, but not necessarily their ability to survive. • Darwin proposed this process after observing that organisms within some species possess characteristics that enhance their ability to reproduce but hinder their ability to survive. Psychology 305

8. Darwin maintained that there are 2 mechanisms through which sexual selection occurs: (a) Intrasexual selection • Occurs when same sex organisms compete for the sexual interest of the opposite sex. • Organisms that possess characteristics that enable them to “win” the sexual interest of the opposite sex are more likely to mate and to pass these characteristics on to the next generation. Psychology 305

9. Offspring that inherit these characteristics, in turn, are more likely to mate and to pass the characteristics on to yet the next generation. • Through this process, the characteristics that enabled the victors to win increase in frequency across successive generations of the species until they come to characterize virtually all members of that sex of the species. Psychology 305

10. E.g. of a characteristic that has evolved through intrasexual competition: The Ariel Hover Display among male Bronzed Cowbirds (used to attract the sexual interest of females). Psychology 305

11. (b) Intersexual selection • Occurs when organisms of one sex prefer to mate with organisms of the opposite sex that possess specific, desirable characteristics. • Organisms that possess characteristics that are desirable to the opposite sex are more likely to mate and to pass these characteristics on to the next generation. Psychology 305

12. Offspring that inherit these characteristics, in turn, are more likely to mate and to pass the characteristics on to yet the next generation. • Through this process, characteristics that are desirable to the opposite sex increase in frequency across successive generations of the species until they come to characterize virtually all members of that sex of the species. • E.g. of a characteristic that has evolved through intersexual selection: The brilliant plumage of the male peacock. Psychology 305

13. In recent years, evolutionary biologists have come to believe that natural selection and sexual selection operate through differential gene reproduction. • That is, they have come to believe that organisms with highly adaptive characteristics pass their genes on to subsequent generations at a greater frequency than organisms with less adaptive characteristics. Psychology 305

14. Evolutionary psychologists have adapted the principles of evolutionary theory to the study of personality. • They believe that our basic psychological processes are the product of natural selection and sexual selection. Psychology 305

15. What hypotheses has the evolutionary approach generated regarding altruism? • Altruism: Refers to a desire to help others, even at the risk of one’s own well-being. • After the discovery of genes, Hamilton (1964) proposed the theory of inclusive fitness. This theory maintains that organisms are motivated to enhance their own survival and reproductive potential, as well as the survival and reproductive potential of those who are genetically similar to them. Psychology 305

16. On the basis of Hamilton’s theory, evolutionary psychologists generated two hypotheses regarding altruism. • Hypothesis A: Helping behaviour increases as the degree of genetic overlap increases between the helper and the recipient. • Hypothesis B: Helping behaviour increases as the reproductive potential of one’s kin member (i.e., relative) increases. Psychology 305

17. Burnstein et al. (1994) tested both hypotheses with participants from the U.S. and Japan. • Asked participants to 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. • In order to test Hypothesis A, participants were presented with people who varied in their degree of genetic overlap with the participant. Psychology 305

18. Results consistent with Hypothesis A.   Tendency to Help   .50 .25 .125 .00 Degree of Genetic Overlap Highly Related Not Related Psychology 305

19. In order to test Hypothesis B, the researchers conducted 2 studies. In the first study, participants were presented with kin members who varied in age. Psychology 305

20. Results consistent with Hypothesis B.    Tendency to Help   1 10 18 45 75 Age of Kin (Years) Psychology 305

21. Presumably, under conditions of ample resources, the reproductive potential of a 1 year old is greater than that of a 10 year old. • Interestingly, when researchers asked participants to imagine that they lived in a country inflicted with famine (i.e., under conditions of limited resources), a curvilinear relationship emerged between the tendency to help and age. Psychology 305

22. Results consistent with Hypothesis B.   Tendency to Help    1 10 18 45 75 Age of Kin (Years) Psychology 305

23. Presumably, under conditions of limited resources, the reproductive potential of a 10 year old is greater than that of a 1 year old. • In the second study designed to test Hypothesis B, participants were presented with kin members who varied in health. Psychology 305

24. Results consistent with Hypothesis B.  Tendency to Help  Healthy    Sick  .50 .25 .125 Degree of Genetic Overlap Highly Related Not Highly Related Psychology 305

25. 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. • Reproductive capacity: Males > Females • Females: Can bear 8 – 12 offspring across the lifespan. • Males: Can bear an almost unlimited number of offspring across the lifespan (maximum recorded to date: 900). Psychology 305

26. 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. • 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. Psychology 305

27. In order to maximize their reproductive potential, males employ strategies that enable them to copulate with as many females as possible. • In order to maximize their reproductive potential, females employ strategies that restrict copulation to males who are able to provide care and resources for the offspring. Psychology 305

28. Following from these strategies, evolutionary psychologists have generated 2 interrelated hypotheses regarding sex differences in the desire for sexual variety: • 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. Psychology 305

29. Studies that have tested these hypotheses include the following: • 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: Psychology 305

30. Percent Who Agreed MaleFemale “Would you go out on a date with me tonight?” 50 55 “Would you go back to my apartment with me tonight?” 69 6 “Would you have sex with me tonight?” 75 0 Psychology 305

31. These results are consistent with Hypothesis A. • Buss and Schmitt (1993) • Asked unmarried male and female participants how many sex partners they would like to have in the next month, the next year, the next 5 years, and so forth, through to the end of their lives. Psychology 305

32. Results consistent with Hypothesis B. 20  Males  15  DesiredNumber of Partners   10   Females  5           0 1 2 3 4 5 10 20 Life Time (Years) Psychology 305

33. What hypotheses has the evolutionary approach generated regarding sex differences in jealousy? • Evolutionary psychologists maintain that, once a mate has been selected with whom to copulate, males and females encounter different adaptive problems. • Females: Must ensure that their mates do not withdraw care and resources, as this would jeopardize the survival of offspring. • Males: Must ensure that their mates do not copulate with other males, as this would result in uncertainty regarding the paternity of offspring. Psychology 305

34. Following from these adaptive problems, evolutionary psychologists have generated 2 interrelated hypotheses regarding sex differences in jealousy: • Hypothesis A: Females are more likely than males to become jealous in response to cues that suggest emotional infidelity. • Hypothesis B: Males are more likely than females to become jealous in response to cues that suggest sexual infidelity. Psychology 305

35. Studies that have tested these hypotheses include the following: • Buss, Larsen, Westen, & Semmelroth (1992); Buunk, Angleitner, Oubaid, & Buss (1996) • Presented participants with the following dilemma: Psychology 305

36. Think of a serious, committed romantic relationship that you had in the past, that you currently have, or that you would like to have. Imagine that you discover that the person with whom you’ve been seriously involved has become interested in someone else. Of the following, what would distress or upset you more? • Imagining your partner forming a deep emotional attachment to that person. • Imagining your partner enjoying passionate sexual intercourse with that other person. Psychology 305

37. Results consistent with Hypotheses A and B. Percentage Reporting More Distress to Sexual Infidelity Psychology 305

38. Buss, Shackelford, Kirkpatrick, Choe, Hasegawa, Hasegawa, & Bennett (1999) • Had participants imagine that their partners had become both sexually and emotionally involved with someone else. • Asked participants to indicate which aspect of the infidelity they found more upsetting. Psychology 305

39. Consistent with Hypotheses A and B, the researchers found that: (a) 63% of the males but only 13% of the females reported that the sexual aspect of the infidelity was most upsetting. (b) 87% of the females but only 37% of the males reported that the emotional aspect of the infidelity was most upsetting. • Subsequent studies (e.g., Wiederman & Kendall, 1999) have produced similar results in other cultures. Psychology 305

40. What hypotheses has the evolutionary approach generatedregarding birth order and personality? • Most animals, including humans, require some degree of parental investment (i.e., investment of parental resources) in order to survive. • When parents have more than one offspring, siblings must compete for parental investment. • Evolutionary psychologists maintain that first-born children (FBs) and later-born children (LBs) have developed different strategies to maximize parental investment. Psychology 305

41. E.g. of strategies used by FBs 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. Psychology 305

42. For humans, evolutionary psychologists have generated several hypotheses regarding the strategies that FBs and LBs use to maximize parental investment and the impact that these strategies have on personality. Hypothesis A: FBs are more likely to attempt to dominate younger siblings; this should result in higher levels of dominance and assertiveness (i.e., extraversion) among FBs. Psychology 305

43. Hypothesis B: LBs are more likely to cooperate with older siblings in order to avoid physical confrontation (thereby allowing them to engage in other actions that will increase parental investment); this should result in higher levels of cooperativeness and compliance (i.e., agreeableness) among LBs. Hypothesis C: Both FBs and LBs are likely to try to help their parents; however, FBs are asked for help more frequently than LBs; this should result in higher levels of dutifulness and responsibility (i.e., conscientiousness) among FBs. Psychology 305

44. Consistent with these hypotheses, several studies have shown that (see Sulloway, 1996): • FBs > LBs in extraversion • FBs < LBs in agreeableness • FBs > LBs in conscientiousness Psychology 305

45. Questions That Were Answered in Today’s Lecture • Biological Perspective on Personality: Evolutionary Approach • What are the basic principles of evolutionary theory and how have they been adapted to the study of personality? • What hypotheses has the evolutionary approach generated regarding (a) altruism, (b) sex differences in the desire for sexual variety, (c) sex differences in jealousy and (d) birth order and personality? Psychology 305