Transcript 4. Sexual Selection

4. Sexual
Selection
Starter
• Describe what you think makes the
following people attracted to each
other;
• Catherine Zeta Jones and Michael
Douglas
• David Furnish and Elton John
• Jay Z and Beyonce
Learning Objectives
• Explain reasons why certain features are
attractive to men and women and will be
able to describe what men and women
seek in potential partners
• Describe research which has
demonstrated these factors
• Describe the link between sexual
selection and human reproductive
behaviour
Big Picture
• Define sexual selection
• Make notes about research into
sexual selection
• Plan and answer a question about
sexual selection and human
reproductive behaviour
Natural & Sexual Selection
• Natural selection
– Ability to survive in a particular environment
(fitness)
• Sexual selection
– Ability to attract/find a mate and reproduce
successfully
• These are separate processes – the
characteristics that facilitate reproduction
do not necessarily increase survival
chances
Natural Selection
• The animals who adapt to their environment
survive and manage to pass on adaptive
characteristics to their offspring
• An example is: The humans whose memory is
good will remember which berries are safe
and which ones are poisonous.
• What will happen to those whose memory is
poor?
• What will happen to their offspring?
• Come up with one more example
Sexual Selection
• Characteristics evolve because they
have been passed from one
generation to the next via the genes
• This requires the organism:
– To live to reproductive age
– To mate successfully
– To ensure the offspring’s survival
Sexual Selection
• The peacock (the male) is sexually
successful because of his attractive
plume
• If the female has a choice, she will
choose him over another peacock with
a less attractive plume
• What is the benefit to him?
• What is the benefit to her?
• What is the benefit to their offspring?
• What will happen to his genes?
Evolution & mate choice
• Sexual selection suggests that males
& females adopt different mating
strategies
– Male – relatively indiscriminate,
interested in fertility of potential mate
– Female – relatively discriminating,
interested in ability of potential mate to
provide for offspring
Inter and Intra sexual selection
• Intrasexual selection (mate
competition) – members of one sex
compete with each other for members of
the opposite sex
• Intersexual selection (mate choice) this
involves the preferences of one sex for
members of the opposite sex who possess
certain qualities e.g. economic factors for
humans
• DARWIN (1874)
Sexual Dimorphism
Key word: Sexual dimorphism, when males and females develop
different characteristics in order to be successful in reproducing
Personal ad research
• Some evolutionary researchers have
looked at the personal ads people
place when looking for a partner
• These are short & succinct, with
(usually) clear indications of:
– The characteristics sought
– The characteristics offered
Task
• Examine the personal ads with the
person sitting next to you
• Pick out the characteristics that the
person is looking for and offering
• Decide whether they are physical or
non-physical
Evolutionary hypotheses
• Men are looking for women who are
likely to reproduce successfully
– Young
– Physically attractive
• Women are looking for successful
men who can provide for offspring
– Older
– Successful/rich/high status
Waynforth & Dunbar (1995)
• Method
- used 900 personal ads in USA
• Age
– M asked for F 1-12yrs younger than them; F
for M 2-7yrs older
• Attractiveness
– M mentioned own attractiveness 1.4x less
than F; asked for attractiveness 2x as often
• Resources
– M mentioned own wealth 1.7x more than F; F
asked for wealth 4.5x more than M
Buss (1989)
• Cross cultural comparisons (37
different cultures) Survey of 10,000
people-what people looked for in a
marriage partner
– F placed higher importance (average
2x) on wealth in all cases
– F preferred older partners (average
3.5yrs) in all cases
– F placed more importance on education,
qualifications, career
Pawlowski & Dunbar (1999)
• Personal ad study
– Women generally make more demands
in personal ads (i.e. mention more
selection criteria)
– Women were more likely than men to
withhold info about their age & this
tendency peaked between 35-50 years
old
– This supports the evolutionary
hypothesis because…
Progress Checker
• A man has broad shoulders and is
intelligent, he is chosen by a woman
to have children with. This is an
example of…
• A female is able to find food in the
winter due to her intellectual and
cognitive abilities, therefore she
survives to have children. This is an
example of…
Short term mating preferences
• Men have evolved a greater desire
for casual sex
• Would be more beneficial for them to
impregnate as many women as
possible over a period of time
• Women can only have one child in 9
months, no matter how many times
they engage in sexual activity
Long term mating preferences
• Women more than men desire mates
with financial success
• Men more than women place large
importance on physical
attractiveness
• Men want women who possess
physical characteristics which
demonstrate fertility,including youth.
Short term mating
preferences
• What does this refer to?
• Who are ST mating preferences more
applicable to?
• What were the findings of Buss and
Schmit’s research?
• What conclusion can be drawn?
• Why are men able to have short
term relationships as opposed to
women?
LT Mating preferences
• What are the physiological
differences that mean women need
LT relationships?
• What are women looking for?
• http://www.youtube.com/watch?v=
wqXrQPfW8oE
Group work
• Explaining short term or long term
mate preferences write a paragraph
using:
• Point
• Evidence
• Explain (why it is an evaluation)
• Link
Read
• Clarke and Hatfield (1989) ST Mating
Preferences – Blue box
• Miller et al (2007) Importance of
fertility – Blue box
• Penton-voak et al (1999) – Female
mate choice varies during menstrual
cycle.
• Kenrick et al 1996 – more about
social power than mating preference.
• Younger women easy to control.
Clarke and Hatfield (1989)
• https://www.youtube.com/watch?v=
qkkQxv9m0R8
Task
• Answer the following question –
• What is the relationship between
sexual selection and human
reproductive behaviour?
• Talk to the person sitting next to you
• What does this question mean?
• What are the main points?
• How can we structure it?
• Introduction to sexual selection
(define what it means)
• Describe a piece of research on
sexual selection and what they have
found
• Describe how sexual selection affects
human reproductive behaviour
• Commentary/evaluation of these
points
Review
• Read out your answers