Biological Foundations

Main sex hormones

Androgens and estrogens

• Males and females can produce both types but at varying levels and at different times

• Males: high lvls of tesosterone prenatally, first few weeks of life, and from puberty onwards

• Females: high lvls of estrogen prenatally and starting in puberty to menopause

Organizational effects of hormones

Causes permanent changes to structures in the body

Activational effects of hormones

produce temporary changes to physical functions

How does early exposure to androgens (testosterone) affect behavior?

1. People with CAH (Congenital Adrenal Hyperplasia): males/females who produce higher than normal androgen lvls prenatally

2. Twins: boy-girl pairs vs girl-only pairs

3. Correlating hormone lvls of mom or amniotic fluid to gendered behavior

Are there hormonal bases to toy and activitiy preferences?

Yes, CAH females spend more time playing with boys’ toys and less time with girls’ toys than control females

• Differences continue into adolescence

• Prefer careers like engineer, construction worker, pilot

Toy preferences of rheus monkeys vs human subjects

Monkey preferences are consistent with human preferences

• Male monkeys show preference to boys’ toys and female monkeys preferred dolls

Hormonal effects on emotions

• Androgens linked to high lvls of aggression in boys

• Androgens related to sexual desire: in adult males/females

• Tesosterone therapy increases anger/aggression in trans men

Hormonal effects on cognition

• Estrogen enhances verbal fluency and memory

• Moderate lvls of testosterone enhance spatial ability

Hormonal effects on puberty

• Early maturing girls: more distress and problem behavior

• Early maturing boys are more popular, late maturing have confidence issues

• Effects are stronger in girls

Behavior effects on hormones

Hormones have an effect on behavior but behavior can have an effect on hormone lvls

• Testosterone rises in both males/females after an interpersonal competitive victory

• Women only: when put into competitive situation their testosterone lvls rise

Distribution

The range and frequencies of scores on a given task or measure

Normal distribution

Assumed of large enough sample, population

Measures of central tendency

• Mean (M): average

• Median: score in middle of the range

• Mode: most frequent/common score

Measures of variability

• Variance: summed squared difference from the mean

• Standard deviation (SD): square root of variance

Meta analysis

A statistical technique that allows a researcher to combine the results of many research studies

1. Locate all previous studies

2. Compute the effect size for each study

3. Find average effect size across all studies

Effect size

How large the difference is between 2 samples, given the variability within the samples

• Cohen’s d: a measure of standardized effect size, how far group means are in SD units

Values (d) of effect sizes

• .2 = small

• .5 = moderate

• .8 = large

• +ve d = male score higher

• -ve d = female score higher

Alpha bias

emphasizing difference

Beta bias

minimizing difference

Physical sex differences

• Height: males are taller

• Weight: similar

• Puberty: females start 2 years earlier than men

• Physical strength: boys/girls start out with similar muscle fibers/strength, after age 13 muscle strength increases in males more than females

Primary sex ratio

Hypothetical ratio at conception

• Historically believed to be about 120 males for every 100 females

Secondary sex ratio

• At birth the ratio is 105 to 100

• By age 30 the ratio is equal

• After age 30 females outnumber males

Brain size between men and women

Men’s brains are larger than women’s

• Trans women’s brains are similar in size to cisgender men’s brain size pre-transition

Lateralization

The two brain hemispheres specialize in particular functions

• Connected by the corpus callosum: transission of info across hemisphere

• Left hemisphere: language, analytic thoughts, sequencing

• Right hemisphere: synthesis, simultaneous processing, spatial skills

Brain regions

No consistent sex differences in adults

• Boys: have slightly larger amygdala (emotion processing), smaller hippocampus (learning/memory), and smaller caudate (voluntary movement)

Brain gender mosaic

Each region of the brain is classified as female-leaning (larger in women), male-leaning (larger in men), and intermediate (no difference)

• Most people have a brain that is a mosaic

Neural plasticity

The brain has the ability to change and adapt

Proximal explanations (evolution)

Immediate causes such as genes, hormones, brain

Distal explanations (evolution)

factors that do not immediately precede characteristics

Natural selection

Characteristics that increase survival rate

Sexual selection

Characteristics that increase likelihood of mating and reproducing

Adaptive pressure

The goal of every human is to survive and reproduce

• Females investing time/energy in reproduction: need to be picky about partners, interested in babies

• Males competing to be chosen: need to be showy and agressive

Problems with Evolutionary Psychology

• Claims are hard to test

• Explanations dont account for sex differences (ex: not all men want multiple partners)

• Difficulty of making inferences about adaptive significance