Lecture 2 (Mate Choice 1) - Slides Flashcards Preview

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Sexual Selection

- Differential access to mates (more important) or gametes
- Natural selection operates independently (differently) for the sexes
- Sexual selection may not aid survival, and may impeded it. But it does aid reproduction.


2 Ways to get a sexually selected trait

1) Vanquishing same-sex rivals (intrasexual selection)
2) Being chosen by the opposite sex (intersexual selection)

- May not operate indendently, mate may be more likely to be subject to intersexual selection after an intrasexual competition
- Example: Male deer and antlers are both for competition and are selected by females (Large antlers = better health and fewer parasites, and if they can use them in competitions = strength)


Handicap Principle
(What is the cost balance called and explain)

- Only those individuals in good condition can afford to grow or develop larger more elaborate versions of these traits (does not have to be physical, can be psychological as well.
- Fitness trade-off occurs because it's expensive to develop these signals which could be used for survival
- Everything has a trade-off
- Example: Heightened growth to be bigger and stronger faster heightens aging


Sexual Dimorphism in size
(What is the name for increased intrasexual competition among males, why is there variation in size at all, why not all big?)

- Polygyny: Increased intrasexual competition among males
- Males are 1.06 times larger than females in humans on average
- Why variation? Bigger individuals die earlier - important for grandparenting, and females may mate for resources and other reasons, not just height, but tall males usually have more resources.
- Also depends on female height.
- Monogamous species have similar size/shape/colour between sexes
- The more promiscuous the sexual behaviour, the more dimorphism (Usually male is bigger than female in mammals)
- Size is as good of a threat as ACTUALLY fighting and if competition increases, size becomes more important (Height is an ornament and a weapon)

- Exaggerated ornaments and weapons can occur as part of sexual dimorphism if competition increases


Salska (2008)

- What is your ideal partner height for a romantic relationship
- Women prefer taller males, males are more flexible but perfer shorter
- Preference for height depends on your height as well and average height of men in your potential mate pool
- Indirect benefit of height: Height in males is heritable and will increase likelihood offspring will be more rep


Male tallness benefits and cost

- Intimidate rivals, win physical competitions, provide resources and may cue status
- Cost: Senescence, difficult to achieve


Sex Differences in Reproductive rate

- Women are constained by pregnancy, gestation, and lactation, limited conception risk (can only get pregnant at certain times)
- Men is limited only by the access they have to mate (and puberty), but have higher variance/death rate due to competition.
- On average most have 2-3 children, in natural fertile non-industrial cultures it's higher


Bateman's Principle

- The sex with more variance in reproductive success will compete for access to the sex with less variance in reproductive success
- In humans, females are not able to reproduce as often as males for many reasons and therefore are more selective and males will be more competitive - the OSR is skewed to males
- Results in some males mating with multiple females, and some males not at all.


Operational Sex Ratio

- Ratio of sexually mature males to sexually mature females that are available to mate.
- Sex ratio = regardless of sexually mature available to mate (107-100 males-females in humans)
- Influenced by differences in: Reproductive rate, sexual maturation, mortality
- Causes men to compete more (not enough women to go around) and females to be choosy about mates (to have higher standards)


Examples of OSR
(Natural effects and cultural events)

- Young male syndrome: more male offspring born, but they die more usually do to more risky behaviours (still will have a male skew in OSR)
- Single Child Law in China


Triver's Parental Investment Theory

- The sex that invests less in offspring will compete for the sex that invests more.
- The sex that invests more in offspring will be more discriminative in selecting mates than will the sex that invests less
- Not all women release an egg in an ovulatory cycle and there is variation in egg quality


Factor's Influencing Parental Investment

1) Anisogamy: - Differences in gametes (Sperm are smaller and produced in huge quantities (12mil/hour), Ova are larger and 400/lifetime)

2) Gestation: Huge maternal investment and women prefer/mated with men who gave them more resources. Lactation further suppresses fertility

3) Post-natal care: women tended to be in contact with infants more than fathers


The Coolidge Effect

- Males exhibit renewed sexual interest if introduced to new receptive sexual partners even after refusing sex from prior but still available sexual partner
- Males produce more sperm in their ejaculate to a new partner
- Women going on dates are more preoccupied with looking different, may be related to this.
- Men are more likely than women to benefit from additional mate opportunities


Desire for number of mates
(Bride wealth)

- Male reproductive success benefits from increase in wives
- Payment made by a groom or his kin to ratify a marriage
- In some cultures the dowry is about the same as ring
- Men want sex with a new partner earlier than women, want more partners over 30 years and consent to sex earlier.
- Africa is very low, likely due AIDS and sex education
- Bride wealth positively correlates to how early female was circumcised (when she hit puberty. Earlier puberty = more fertile)


Clark and Hatfield 1989

- Asked attractive confederates to ask out strangers.
- Men and women will equally go on a date, but apartment/sex option was way more men, and men apologized when they did say no



- Males prefer younger women because they can have more offspring (Higher reproductive value)
- Females prefer older men because reproductive value is not contingent on age, but they are more likely to have more resources


Male Sexual Opportunism vs. Female Choosiness (Reflected in?)

Male: Desire for higher number of partners, shorter time to mate, lower threshold of mating attempts
Females: Desire for lower # of partners, longer time to mate, higher threshold of mating attempts


Fieder & Huber 2007

- Men who are 45-55 year old and married to the same woman and who was younger had more children


Bus 1989

- Surveyed 37 cultures and asked how important financial prospects are in a marriage partner.
- Much more important for females


Waynforth & Dunbar 1995

- Examined Lonely Hearts ads (what they wanted, and what they offer)
- Women across almost all ages post that they are seeking resources, men post they are offering resources
- Resources might not be shared though so cues to investment of family must also be important
- Women seek cues to family more than men and men offer it at the same rates as women (preference for resources)
- Men prefer and seek cues to physical attractiveness (2x more), and women offer it (Preference for fertility) but want it too (in health)
- Women seek ambition more than wealth for various reasons


Preferences for Fertility
(Also, 2 types of ovulation and why did it evolve)

- Concealed vs overt ovulation
- Overt Ovulation: Reduces mate search time, increases probability copulation results in pregnancy, mate guarding (dont have to guard all the time), increases paternity certainty, if concealed in both it increases likelihood of larger intrasexual competitions.
- Concealed Ovulation: Could increase monogamy, paternal beavhiour, deceive males into cuckoldry, risk of infanticide, reduce harassment from rival females


4 Indicators of fertility and examples

1) Behaviour: Females in estrous are friendlier, dress more provactively and spend more time and effort on cosmetics
- Move differently, looser in estrous.
- Lap dancers receive more tips when they are ovulating

2) Smell: Men smelled tampons (Doty et al, 1975) and t-shirts (Thornill et al., 2003) and found ovulatory phase more attractive

3) Sound: Voices are more attractive based on their conception risk (ovulatory cycle)

4) Sight: Prefer ovulating faces more


Evolutionary Arms Race (males vs. females)

Males benefit from knowing reproductive status of women, women benefit by concealing this status to attract mates into more paternal investment, increase monogamy, reduce infanticide (paternal certainty)