Week 5 Lecture 5 - sex Flashcards
What is the cost of meosis?
only half of one’s genes go to offspring
What is the cost of courtship and mating?
have to first find a mate and then convince them to mate
What population will grow exponentially, a sexual population or an asexual one?
an asexual one
What is Fisher’s principle?
- a sexual pop. should produce an equal number of males and females (1:1)
- the rarer sex is at an advantage
What is the Red Queen Hypothesis?
- reproduction is an arms race in a constantly changing environment
- explain extinction and evolution of sex
What environment changes rapidly enough to fit with the Red Queen Hypothesis?
parasites, harmful bacteria, disease etc.
need diversity to overcome these
Do you need faster or slower evolution to overcome rapidly changing enviroments?
- faster evolution
- genetic variability to adapt to changing environments (Fisher)
What is Muller’s ratchet?
accumulation of harmful mutations in asexual species
What are raffles?
sex in more unpredictable environments
What is the best theory for the evolution of sex?
Red Queen Hypothesis –> adapting to parasites
What is sexual selection?
differences among individuals in mating success
- often appears to run contrary to natural selection
What is sexual asymmetry?
- the difference between males and females of a species
Where does sexual asymmetry stem from?
the principle of gametic differences
What is the principle of gametic differences?
eggs are more expensive than sperm
females are more “precious”
What in Intrasexual competiton?
males have to compete with other males for access to females
What is intersexual competition?
females have fewer opportunities to mate and must be discriminating
True or false?
Males are more invested in competition and females invest more in offspring
True
What is runaway selction?
females choose for ‘best’ males
- daughters more likely to choose the same traits
- sons more likely to have those traits
What is parental investment theory (Trivers)
across species, females typically invest more the the offspring
What are 2 other theories of sexual asymmetry?
- Handicap principle
- Parasite theory
What is the Handicap principle?
ornaments honestly signal quality by being costly
What is parasite theory?
ornaments are a direct display of health (parasite resistance)
What is reproductive skew?
males typically have greater variance in reproductive success than females
What was Anderson’s study on female choice?
- manipulated tail length of male widowbirds
- territories were all of equal size
- females 4 time more likely to nest in long-tailed male territories
What percentage of males and females, across societies, report having same-sex partners?
2-10%
Is there a single continuum for opposite-sex to same-sex preference?
no
Do some people argue that there is a biological basis for homosexuality?
What is this?
yes but based largely on correlational evidence
- homosexual males may be “good uncle” –> forgo having offspring to provide more nurturing care
- homosexuality may be a by product of other traits
What are mating systems?
sexual relationships among males and females
What is polgyny?
one male mates with several females
what is effective polygyny?
greater variance in male reproductive success
What is the result of polygyny?
greater sexual dimorphism –> larger males have more mates
Where is polygyny found?
- most mammals
- 2% of birds
- in humans: permitted in most societies (83%), accounts for less than half of marriages
What is the polygyny threshold model?
females can be better off (higher fitness) by mating with a male who already has a mate (bigamy) because of qualities of the male
e.g., territory, food supply etc.
What is polyandry?
one female mates with several males
What is effective polyandry?
greater variance in female reproductive success
Where does polyandry exist?
- virtually non-existent in mammals
- <0.5% of birds
- humans: 0.5% of societies
What is polygynandry?
males and females mate with more than one partner
What is monogamy?
one male mates with one female
What is serial monogamy?
mate and separate
Where does monogamy occur?
- in some ungulates and primates, carnivores and a few mammals
- occurs in 92% of birds
- humans: 16% of societies permit only monogamy
Who tends to benefit most from monogamy?
females
Who tends to benefit most from polygyny?
males
What is Bateman’s rule?
the sex that invests more in offspring is the resource to be competed for by the other sex
What are the 2 main types of mating strategies?
short term and long term
What did David Buss find when researching what people look for in an ideal mate?
many similarities e.g., mutual attraction, dependable character, emotional stability, pleasing disposition
What are the costs and benefits of male STM?
costs:
- STDs, reputation, lower offspring survival, Intrasexual aggression, retaliation
benefits:
- even a small increase in number of offspring produced can outweigh costs
What is the Coolidge effect?
males should look for any available mating opportunity; they are therefore more attracted to novel females
What do males prefer concerning variety and number in STM?
- males do desire more sex partners
- lower standard for STM
- short time lags between meeting a partner and seeking sex
What do males prefer concerning accessibility in STM?
sensitivity to behaviour signalling sexual readiness
What do males prefer concerning closing time in STM?
- lower standards for age, intelligence, compatibility, reputation, personality
- standards becomes even lower when likelihood of success diminishes
Do males in STM avoid commitment?
yes
What is an EPC?
extra-pair copulations
What do males prefer concerning EPCs in STM?
- males seek more extramarital affairs
- males seek sex workers
What are the costs and benefits of STM for females?
costs:
- unwanted pregnancy, reputation, loss of resources from mate, abuse
benefits:
- resources, genes, mate inspection
What do females prefer concerning resources in STM?
- meat, shelter, services, protection
- assess resourcefulness of males
- career enhancement
Why might EPCs occur for females in regards to resources?
current partner might not be a good provider
What do females prefer concerning genes in STM?
- novel mates contribute to outbreeding - introduce new alleles to offspring
Why might EPCs occur for females regarding genes?
current partner might be infertile or not performing
What do females prefer concerning male switching in STM?
- affairs can aid in dropping a stale mate
- current mate may also be having affairs
- women value commitment in ST mates more than males
What is the role of self esteem in STM?
- high sexual esteem males have more STM
- high sexual esteem females have fewer STM, whereas low esteem females have more STM
Why might males choose monogmay?
- non-monogamous males aren’t as likely to mate
- monogamous males have wider choice of females
- paternity certainty
- improved offspring survival
Why might males by choosy?
- sperm is cheap, sex is not
- in LT mates, males choose good mums, for ST they choose sexual enthusiasm
What do males prefer concerning fertility in LTM?
- fertile female
What is fertility rate?
the number of children an average woman gives birth to
Is fertility difficult to observe?
yes (loss of oestrus)
ovulation concealed, sexual activity acyclic
What is reproductive value?
potential future reproductive output
What do males prefer concerning youth in LTM?
- men desire younger women (average by 2.5 years)
- age difference increases with age of male
- teenager prefer women a few years older (closer to fertility)
What do males prefer concerning beauty in LTM?
- physical youthfulness
- behavioural youthfulness
- males value beauty of a mate more than females
What do males prefer concerning symmetry and averageness in LTM?
- symmetry is an indicator of health, age and good development
- face must still conform to population average
What do males prefer concerning waist to hip ratio in LTM?
- WHR of 0.7 is preferred
- health and fertility correlated with this
What do males prefer concerning ovulation in LTM?
- ovulating females should be more precious, therefore mate selection and mate-guarding should peak
- ovulating females may present subtle cues that they are ovulating –> males may only be responding to cues
What do males prefer concerning paternity certainty in LTM?
- increased paternity uncertainty could lead to increased mate-guarding and hence monogamy
-premarital chastity and post marital sexual fidelity assure certainty
What do males prefer concerning context and reality in LTM?
- when in a position to choose, males select youth and beauty
What do males and females advertise respectively?
males advertise resources
females advertise appearances
Why do females choose LTM?
- higher parental investment
- must be more careful to avoid bad matings
What do females prefer concerning resources in LTM?
- evidence of “providers”
- resources should be accruable, defensible and controllable
- future financial prospects
- females value status, ambition and other resource traits in long-term mates
What do females prefer concerning status and age in LTM?
- position in hierarchy reflects ability to hold resources
- education and professional degrees count
- status often improves with age
What do females prefer concerning dependability and stability in LTM?
- emotionally unstable men are more harmful
What do females prefer concerning physical condition LTM?
- athletic ability can mean protection
- choose males that are winners
- resist males to test their endurance and to attract competitors
- health indicates good genes and reduced parasites
- select for traits that are hard to fake
What do females prefer concerning fluctuating asymmetry in LTM?
- indicator of potential developmental defects
What do females prefer concerning 2D:4D in LTM?
- lower ratio linked to prenatal androgens
- correlated with assertiveness, aggressiveness, athleticism, risk taking
What is 2D:4D?
ratio of 2nd digit to 4th digit (index finger to ring finger)
What do females prefer concerning love and investment in LTM?
- assess willingness to commit and invest resources
- want to ensure monogamy
What do females prefer concerning mated males in LTM?
- mate with a male that other females choose
- rely on their experience and save time
