[2] sex differences in humans

behavior sex differences in humans

studying this discipline is often a challenge as there is often overlap between males and females for most behaviors and more variation within each sex 

effect size

the measure of variation between sexes after accounting for variation within each sex; must be considered when studying behavioral sex differences in humans

1. hormones/biological factors

2. environment/social factors

3. interaction between hormones/biological factors and environment/social factors

causes of human behavioral sex differences

sex

biological and physiological characteristics that distinguish females from males

gender

socially constructed roles, behaviors, activities and attributes that a given society considers appropriate for boys/men and girls/women

• specific to humans ONLY

gender roles 

collection of behaviors or attitudes that are considered appropriate or normal for each sex 

• culturally specific

CAH and 5(a)-reductase deficiency studies and gender roles

hormones may play a role in gender roles

gender identity

psychological self-perception of being male or female

cis-gender

alignment with gender identity with sex assigned at birth (natal sex)

transgender

people who feel that their natal sex does not match their gender identity 

transgender females

individuals who were assigned males at birth but identify as females

transgender males

individuals who were assigned females at birth but identify as males

3-5 years of age

when gender identity develops in humans

CAH and 5(a)-reductase deficiency and gender identity

hormones may play a role in determining gender identity 

how hormones could affect gender identity

gonadal hormones have organizational effects and direct sexual differenitation of the body/genitals AND the brain in the female or male direction

• these processes are INDEPENDENT and occur at DIFFERENT timepoints, leading to transgender identity

sexual orientation

stable pattern of attraction to members of a particular sex

hypotheseses regarding hormones and sexual orientation

1. hormone concentrations in heterosexuals different compared to gay man/lesbians

2. hormones during early development are involved in sexual orientation

otoacoustic emissions

2D:4D ratio

indirect indicators of prenatal hormonal exposure in gay women/lesbians 

otoacoustic emissions

tiny sounds inner ear produces as it processes sound into neural impulses; lesbians have weaker emissions compared to heterosexual women

2D:4D ratio

lesbians and heterosexual males have 2D<4D while heterosexual females have 1:1 ratio

birth order effect

the more older brothers a boy has the more likley he will grow up gay

• supported by maternal immune activation theory

maternal immune activation theory

genes on Y chromosome provoke immune response in the mother which gets greater with each successive pregnancy; this immune response may affect the masculinzation of the brain without affecting the gonads or genitals 

genes and sexual orientation

many genes are involved in sexual orientation

Pain

females have lower threshold and display less tolerance to painful stimuli compared to males; women experience more pain in general

olfaction

females are more sensitive to certain types of odors and better than males at identifying odors - sex steriod involvement

taste

females are superior to males in naming tastes and discriminating tastes - sex steriod involvement

audition

females are more sensitive to sound

vision

males have better visual acuity and visual perception

lateralization

tendency of cognitive skills to be concentrated in one hemisphere

• males are more lateralized compared to females

male connectivity

male brains have more connections between each hemisphere

female connectivity

female brains are more interconnected between hemispheres

female bias

perceptual speed tasks

fine motor tasks

mathematical calculations

verbal skills

male bias

targeted directed motor skills

mathematical reasoning

3D visual rotation

spatial ability 

verbal skills

females show better verbal skills; sex differences arise before puberty

FOXP2

gene vital for acquisition of speech and language; males have lower levels of this gene compared to females

visuospatial skills

males are better at this task; sex differences arise AFTER PUBERTY (activational hormonal effects)

left hippocampus

used to males to solve spatial tasks

right parietal and right prefrontal cortex

used by females to solve spatial tasks