1 Psychology 320: Psychology of Gender and Sex Differences Lecture 15

Announcement The meetings for the Peer Learning Community (PLC) for Psychology 320 will be held on: Tuesdays, 4:00-5:00PM Fridays, 11:00AM-12:00PM in room 1909 of the Kenny Building. The first meeting will be tomorrow, October 16 th. Please see the circulated to PLC members on October 13 th. 2

1. Due to unforeseen circumstances, I must change my office hour this week to: 3 Thursday, October 18, 2:30-3:30PM, Kenny 2517 Reminders

4 Office Hour Invitations October 18 th, 2:30-3:30, Kenny 2517 **Please note time change for this week’s office hour**

2. Due to a conference presentation, Jacqueline-Marie (TA for students with last names A-M) must change her office hour this week to: 5 Friday, October 19, 11:30AM-12:30PM, Kenny 3514

6 Biological Theories of Sex Differences 1. What biological theories have been proposed to explain sex differences?

7 By the end of today’s class, you should be able to: 1. discuss the application of evolutionary theory to the study of sex differences. 2. define the terms: reproductive capacity and minimal parental investment. 3. relate sex differences in reproductive capacity and minimal parental investment to sex differences in sexual behaviour and mate preferences. 4. describe the process of prenatal sex differentiation.

8 What biological theories have been proposed to explain sex differences? Biological theories of sex differences can be classified into four groups: 1. Evolutionary Theories  Evolutionary psychologists have adapted Darwin’s theory of evolution to the study of sex differences.

9  Darwin maintained that organisms have two primary goals: to (a) survive and (b) reproduce.  Darwin argued that characteristics that enhance the survival and reproductive ability of organisms increase in frequency across successive generations, resulting in the “evolution” of the species.

10  Evolutionary psychologists maintain that males and females have evolved distinct characteristics in response to sex differences in reproductive capacity and minimal parental investment.

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. 11

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. 12

13  Example 1: Sex differences in sexual behaviour Hypothesis: Given sex differences in reproductive capacity and minimal parental investment, males have evolved to seek more sexual partners than females and are less discriminating in their choice of sexual partners than females.

14 Evidence: 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: Clark and Hatfield (1984)

15 “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

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

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

18  Example 2: Sex differences in mate preferences Hypothesis: Given sex differences in reproductive capacity and minimal parental investment, males have evolved to value appearance in a mate more than females, and females have evolved to value resource potential in a mate more than males.

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

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

21 2. Genetic Theories  Sex determination occurs at conception.  The fertilized egg contains 23 pairs of chromosomes— the pair that determines the sex of the individual is pair number 23.

22  Only the sperm cell is capable of contributing a Y chromosome. Thus, the sperm cell determines the sex of the offspring.  Female: Pair 23 contains two X chromosomes. Male: Pair 23 contains an X and a Y chromosome.

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25 Biological Theories of Sex Differences 1. What biological theories have been proposed to explain sex differences?