Evolutionary Psychology Unit 2

What is the natural focus of natural selection?

Reproductive behavior

What do we spend most of our life worrying about?

Sex and mating

Why do we reproduce sexually?

It provides pathogen protection

Why do we not clone our offspring?

Sex provides a fodder for evolutionary change, allowing the lineage to adapt

Disease dense ecologies

Strategies that increase diversity, environments change over time so phenotypes need to respond to that change

Diversified genetic bet-hedging

A mating strategy that increases variability among offspring (multi-mate females mate with multiple males)

Increased variability among offspring

Promotes long-term offspring lineage success in pathogen dense ecologies

Asexuals

Female only

Large sex cells

Female, gametes are less mobile

Small sex cells

Male, gametes more mobile

Size of sex cells

Lay the foundation for all reliably- reoccuring sex identification

Large gametes

Requires greater energetic investment (Have more to lose if the offspring is not successful)

Investment evolution

Evolution will reinforce their need to invest whatever is necessary

Parental investment theory

The sex that invests more is choosier when choosing a mate, while the opposit sex will engage in more competition for access to the limited

The sex with larger gametes

Often invests more after birth

Operational sex ration

Ratio of reproductively available males and females in a population

The lesser investing sex

Overabundant in the operational sex ration (Males)

What does operational sex ratio do?

It puts selection pressure on males to compete to win big or prevent being shut out

Reproduction rate

More males die without reproducing than females

Reproductive value

The number of possible offspring one can possibly have in the future

Males reproductive value

Can have a high number of children but can also have none at all

The Bateman Principle

Because males and females have different reproductive value, the greatest investing sex is a limited resource on the reproductive success of the opposite sex

Lesser investing sex

The more mating opportunities with novel partners —> higher the reproductive success

What does evolution select for?

Greater competition among that lesser investing sex (Aggression)

Cost of making bad mating decisions

Females have a greater cost because they have lower reproductive value

Gender reversal in parental investment theory

In some species, females fight in competition for access to the males

Low male standards and women on birth control

Prefer short-term mating contexts

Sexual Selection

• The selective agent is the opposite sex (Usually females)

• Selects for trails conferring mating advantage

Fisherian Theory of Sexual Selection (Sexy Son Hypothesis)

• Not all prospective mates are preferred equally

• Those possessing ‘sexier’ traits get chosen as mates

• Sexy traits get passed down

Cardinal Birds

Females prefer brights red males so less bright males do not have the chance to reproduce

Runaway selection

Females express preference for one trail and it gets exaggerated in future generations

Why do females choose they way they do?

It provides an advantage for females offspring to have good genes/good health

Mate preference must serve an adaptive function

• Direct benefit

• Indirect benefit

Direct benefit

Directly benefits the female

Indirect benefit

Good genes, good health, reproductive potential

The Handicap Principle (Zahavi)

Only genetically efficient organisms can afford the costs associated with these traits (Colorful displays, large ornaments, and courtship displays)

Costly Signaling Principles

• Metabolically costly to develop and maintain

• Beacon to hungry predators

Ornamentation is only seen in males

Because females are the choosy ones

If male choosiness were to increase…

Females would gain more ornamentation

Female traits that are signs of ornamentation

• Full lips

• Large breasts

Males reproductive risk

It is a better risk dying young than it is to be undesirable and not reproduce (High reproductive value)

Reproductive variation

Can reproduce hundreds of children or none at all

Post reproductive survival

It is more important for females to take care of the offspring, especially in humans

Sex

Sex differences will have overlap and have non-normative patterns

Clusters for each sex differentiated trait

Bimodal → Separate from each gender

Gender

Epiphenomenon of individual sex-differentiated traits that tend to covary with biological sex, on average

How does gender work?

• It creates expectations about behaviors that will be expressed by those of a given sex

• Culturally reinforced

Gender identity

• A collection of traits overlap with those typically expressed by those of your sex’s typical gender

• Can be some traits but not others

Gender dysphoria

Posses more traits in common with the opposite sex

Non-heterosexual orientation and sex-gender mismatch

Is expected in evolutionary psychology because of the bimodal overlap

Variability in evolution

• Is essential

• Non-normative patterns of everything are explainable by science

Direct benefits of mate preferences

• Benefits the mate’s fitness directly

• i.e out to dinner, resources, investment, time

Indirect benefits of mate preferences

• Benefits offspring or other genetic relatives fitness

• i.e sexy genes

Reproductive capacity

• A mate’s ability to conceive, bear, or rear offspring

• i.e young, health, fertility

Partner Preference Study

Western and non-western men and women value kindness and understanding in a partner

Women mate prefereneces

• Able to invest

• Willing to invest/commit

• Physically able to protect

Where do women place their importance when finding a long-term mate?

• Financial resources

• Ambition and prosperousness

In every society

Women prefer men with financial prospects

Education and mate preferences

Men get more attractive the higher education they have while women stay the same

Men rated as more attractive

When in high status car or business attire

Does status preferences predict real-life choices

No, but people’s ideas are predict partners. Prediction preferences guide our choices to a good mate

When mate choices are constrained

People must make tradeoffs with their mate preferences

Origin of prediction preference

• Preference provides women with resources for themselves and their children

• Prediction preference is a by-product of sexism

Gender equal countries and prediction preferences

Mate preferences in gender equal countries are the same in sexist societies

Women who have their own resources

Value more resources in their mates, hypergamy

When men don’t have resources

Do not value good financial prospects in women more than men with stable resources

Contemporary women

• Outpace men in college graduation

• Enroll in college more than men

Changing resource, changing markets

Both sexes prefer attractive profiles regardless of education level

High educated women

Favor high educated men

High educated men

Favored less educated women

People most likely to stay single

• Unattractive, low educated men

• Unattractive, high educated women

Mens desirability

Rises until age 50

Womens desirability

Declines from age 18

Preferences in simulated economy

• Fake society with low and high income and gender wage gap

• Lower income group, strong preference for a partner with resources in both sexes

• Age preferences did not change except men prefer younger and women prefer old

Men’s rated wealth

Was more important when women were present

Priming a mating mindset

• Women saw attractive men, men saw attractive women (control group wrote about a day in the city)

• Participants wrong about a date with the attractive person

• Men were willing to spend more on conspicuous goods

• Women’s spending did not change

Men who overspend on conspicuous goods

Are most likely looking for short term mates

Women who see men with flashy things

The man is more desirable for short-term flings and are more interesting

Women prefer older men

• At least 3.5 years older than them (Cross cultural)

• Older age comes with resources, physical strength, wisdom, maturity, and status

Women prefer tall men for dates and mates

6ft tall or at least 6 inches taller than self

Why do women prefer taller men?

• Good genes

• Resource acquisition advantage in the past (and now)

• Familial resource access

Men and height

Women want taller men more than men want shorter women

Countries who vary with height

Tend to have some diseases, pathogens, and unsanitary areas that can lead to shorter people because the body fights diseases instead of using energy to grow height

Tall men

Are seen as more competent and are placed in positions of power more than short men

Women’s preferences in men

Willingness to invest in children

Woman as the greater investing sex

Men assume women will be investing in offspring, so they don’t list it as a preference in women

Men interacting with babies

Men are seen as more attractive when they are positively interacting with a baby, and unattractive when ignoring a baby in distress

Interest in infants invenoty

• Men had their picture taken and gave a saliva sample to measure testosterone

• Men had to choose between adult and infant pictures for babies, kittens and puppies

• Women rated positivity towards long term partner and short term partner

• Women felt more positive towards men who scored high on the interest-in-infant measure

Women choosing for long term mate

They don’t pick the mate with the highest testosterone

Women desire good genes in partners

• Symmetrical faces

• Strength (immunosuppressive, muscles burn calories)

• High testosterone (immunosuppressive, well-functioning immune system)

• MHC, scent = compatibility, diverse MHC genes

Our brain perceives certain features to be attractive

Asymmetry is from bad genes, pathogens, and mutations

Asymmetry

Is linked to high mutation load

Women short term partner

Similar to qualities women want in an extra pair mate

Extra pair mating (Cheating)

Northern Europe extra paternity rate- 11% of children are not really the child’s father

Uncertainty about paternity

~30% of men

Testicle size

Correlates to amount of ejaculate a male releases

Male Chimps (Promiscuous female population)

Have large testicles because more ejaculate is released to ensure the male becomes the father

Monogamous species (Monogamous females)

Have smaller testicles because they are not competing with fatherhood with other males

Male Gorillas

Have smaller testicles because they father all the offspring

Extra pair paternity rate

1-2% (rare in stable relationships)