1. How many surrealists does it take to change a lightbulb?
TWO ...
1 to put the zebra on the giraffe
And 3 to fill the bathtub
with balloons

2. Differences in Reproductive Behaviour and Parental Investment
First, a reminder of your syllabus:
Evolutionary explanations of human reproductive behaviour
• The relationship between sexual selection and
human reproductive behaviour
• Sex differences in parental investment
To note: In the 2012 syllabus the following has changed:
“Removal of parent-offspring conflict and focusing on sex differences in parental investment”; so ignore anything you come across on parent-offspring conflict!!

3. Lesson objectives:
1. Know what differences research has shown in reproductive behaviours
2. Evolutionary explanation for these differences:
‘Parental investment’ (P.I) theory
3. Evaluation points for evolutionary explanations
 So that’s: HOW men & women differ in reproductive behaviour, WHY these differences might be (evolutionary perspective), and HOW GOOD those explanations are

4. Gender Differences in Reproductive Behaviour
Looking through the following 4 slides , WHY might we have those gender differences in the following areas of REPRODUCTIVE BEHAVIOUR
Casual sex
No. of partners
Jealousy
Sexual fantasies

5. Casual sex Men more likely to have short term relationships
Clark and Hatfield ( )
Male/female confederate makes propositions to Ps:
To go out with them that night
To go back to their house
To have sex with them
 50% of men & women agreed to go out
 75% of men agreed to sex
 None of the women agreed to sex
NB: Lesbians also showed an unwillingness

6. Sexual partners Buss and Schmitt (1993)
Asked Ps how many sexual partners they would like
 Over the next 2 years:
Men wanted an average of 8 partners
Women an average of 1.
 Over their lifetime:
Men-18 partners
Women- 4/5 partners
National centre for health statistics (2009): 29% of men vs. 9% of women report having had 15+ lovers

7. Jealousy and adultery Buss (1992)
Asked men and women to rate the degree of distress they would feel in response to their partner’s unfaithfulness
a) involving passionate but meaningless sex
b) Involving falling in love
He predicted that more males than females would report most distress from sexual infidelity rather than emotional infidelity
Results from 4 different countries supported this
Percentage of respondents reporting
more distress at sexual infidelity
A= USA
B= Germany
C= Holland
D= Korea

8. Jealousy
Buss (1993): Asked participants to imagine their partners having sex or being in love with someone else and measured their psycho-physiological stress responses.
Men more stressed at the idea
of them being sexually unfaithful
Women more stressed at the
idea of them loving someone else

9. Sexual fantasies and dreams
Ellis and Symons (1990):
Men are more likely to report sex dreams, especially involving multiple of anonymous partners.

10. Gender Differences in Reproductive Behaviour
So what does the above research suggest to you? Is there a ‘gender divide’ when it comes to sex / reproduction? Is either gender ‘more casual’ about sex? Why might that be?

11. Ok, let’s push a little bit further now and bring kiddywinks into the equation.
Can the nature of reproduction itself help us understand these gender differences in sexual/reproductive behaviour?
*kiddywinks = children

12. Stats: lone parent families
In the UK there 1.9 million single parent families (this figure has remained consistent since the mid-1990’s), of these :
 1, 690, 000 are lone mothers
 , 000 are lone fathers
What does this tell us?!

13. Parental Investment Theory (P.I.)
Trivers (1972) starts his argument with (in a nutshell!) ...
Best way to maximise males’ reproductive success is to mate with as many partners as possible
Best way to maximise females’ reproductive success is to get the best long term protection/resources for her children
World records: Mother- 69 kids (Mrs. Feodor Vassilyev) Father- over 800 Ismaïl Ibn Sharif (16?? – 1727)

14. Gender differences in Parental Investment
Do women invest more? In your hands outs, read p.96 and p.56; make sure you understand how the following factors relate to P.I differences:
Brain size (big headed babies!)
Minimum costs of having a baby (40 weeks vs. a few minutes)
Cuckoldry
Sexual and emotional jealousy
Anything else?

15. So let’s recap what you’ve done......
You’ve looked at Natural & Sexual Selection and what features males look for in females and vice-versa
Gender differences in reproductive behaviour (i.e. differences in how men and women ‘do’ reproduction / relationships)
The evolutionary explanations (P.I) as to why these differences arise

16. THE PARENTAL INVESTMENT PROBLEM PAGE
Consider the following problems and decide if they support or refute the evolutionary explanation of sex differences in parental investment…

17. Dear Deirdre,
My problem is that I think my parents may be splitting up. Ever since I can remember Dad hasn’t been that interested in what I do, and recently he seems to be spending more time in the pub with his friends. What can I do to keep them together?

18. Dear Deirdre,
My mum has recently got a new boyfriend and although he seems okay he always wants us to go out with his own children as ‘one big family’. I don’t want to upset anyone but I don’t want to spend every weekend with them all. What should I do?

19. Dear Deirdre,
I am writing to you because I have just found out that my ‘dad’ is not my real ‘dad’ and I am devastated. It turns out my real dad was a body builder who briefly lived next door to us; my mum has begged me not to say anything but I don’t know if I can keep such a secret from the man I have believed to be my father.

20. Dear Deirdre,
My problem is that since my mum got a new job she seems to be a changed person. My dad recently lost his job so he now stays at home while mum goes out to work. Recently she seems to be coming home later and later and she doesn’t seem to have time for me anymore. What should I do?

21. Dear Deidre,
I have just found out that my parents have been lying to me. My mum couldn’t fall pregnant with my dad so they agreed to go through IVF with a sperm donor and I was born as a result. Both my parents have shown me nothing but love; but how could they have kept this from me?

22. TASK 1: Create a spidergram outlining the parental investment theory theory with all the relevant bits of research on there (make it nice, no chicken-scratch please!) TASK 2: In pairs, go through the example essay provided (‘Critically consider evolutionary explanations of Parental Investment’) and annotate / identify A02 marks. Then break into NEW pairs and share what you have with to the new partner. TASK 3: group-brain-storm an evaluation of the evolutionary explanations (i.e. Parental Investment) of gender differences in reproductive behaviour.