1. The relationship between sexual selection and human reproductive behaviour

2. Sexual Dimorphism Male Male Female Female Male Female
The differences of size, colour, voice and so on between the two sexes in different animal species is known scientifically as sexual dimorphism.
Male
Female

3. Learning Objectives
To be able to understand how and why males and females differ, and the results this has on sexual selection.
Success Criteria
Complete pages of your booklet.
Analyse lonely hearts columns as an indication of our evolutionary past.
Challenge Create a plan for the essay for sexual selection on page 20 of your booklet.

4. Natural Selection
Sexual dimorphism is maintained by the counteracting pressures of natural selection and sexual selection.
Presumably, increased sexual dimorphism means males are brighter and more conspicuous, leading to increased predation.
So long as the reproductive benefits of the trait due to sexual selection are greater than the costs imposed by natural selection, then the trait will increase in the population.
The benefits are a larger number of offspring, while natural selection has the cost in the form of reduced survival.
This means that even if the trait causes males to die earlier, the trait is still beneficial so long as males with the trait produce more offspring than males lacking the trait.

5. Sexual Selection Males tend to be the brighter of the species.
For example, the peacock. The tail of the male you would not expect to be naturally selected, so it must enhance reproductive success in some way.
Key terms:
Intrasexual selection (mate competition)
Intersexual selection (mate choice)

6. Sexual Selection Intrasexual selection Intersexual selection
Members of one sex compete with each other for a member of the opposite sex. The victor will be able to mate and pass on their genes.
Intersexual selection
There is a preference for a trait in a member of the opposite sex, for example, a brightly coloured tail. By mating with individuals with the chosen trait, the trait will be passed on to future generations.
Draw an image on page 17 to illustrate these concepts.

7. Lonely Hearts Analyse the lonely hearts columns. What do males want?
In the short term...
In the long term...
What do females want?

9. Sexual Selection -evaluation-
Make some notes and attach into page 17 of your booklet
Sexual Selection -evaluation-
Being choosy requires time and energy and this could impair survival.
Random mating is stupid mating, because if you are not choosy you will end up with low-quality offspring:
Unattractive
Unhealthy
These low-quality offspring are then more likely to produce low-quality offspring in turn.

10. Short-term mating preferences
Men (according to parental investment theory) desire casual sex, and sex early in a relationship. Over the course of a year males can impregnate a number of women.
Women are not so affected by these evolutionary desires. Woman can only fall pregnant once every 9 months.
According to Buss and Schmidt (1993) men lower their standards in the short-term! AND...show a decrease in attraction following sex in order to make a speedy departure.

11. Short-term mating preferences - evaluation -
Clarke and Hatfield (1989)
Men and women experimenters approached students on a college campus. Said “I find you very attractive would you...
go on a date with me?
go back to my apartment with me?
have sex with me?
Women
0% would have sex
6% would go back to the apartment
Men
75% would have sex
69% would go back to the apartment
Men have a desire for short-term mating, have a desire for sexual variety, have little time between meeting and intercourse, and are willing to have sex with strangers.

12. Long-term mating preferences
Investment in offspring is high.
It pays to be choosy for both sexes.
Buss (2003) found women to be attracted towards males...
who have resources
can physically protect her
show promise as a good parent
are compatible enough to ensure minimal costs to her or the offspring
Males will look for signs of fertility so as not to waste resources.

13. Long-term mating preferences - evaluation -
Buss (1989)
10000 participants
37 cultures
Interested in what males and females look for in a marriage partner. Found:
Women want males with good prospects (resources)
Men placed higher importance on physical attractiveness (and physical fertility health)
Males chose younger women (i.e. fertility)
Both sexes want kind, intelligent and dependable mates
Excellent sample size
Supports AO1 research
Not culturally bias
Individualist and collectivist cultures

14. IDA
Research into mate choice lacks validity because it tells us about what we prefer, but not what actually happens in real life.
But many research studies do support the suggestions, e.g. Buss (1989) studied marriage in 29 cultures and found that men do choose younger women, and after divorce men tend to remarry women significantly younger than them.

15. IDA
Research into short-term mating is gender bias as men could not have evolved to have a desire for short-term mating without willing females.
There must be some benefits (e.g. leaving a poor relationship, or to produce genetically diverse offspring)

16. Essay Planning

17. Learning Objectives
To be able to understand how and why males and females differ, and the results this has on sexual selection.
Success Criteria
Complete pages of your booklet.
Analyse lonely hearts columns as an indication of our evolutionary past.
Challenge Create a plan for the essay for sexual selection on page 20 of your booklet.