Sexual Behaviour

Question 1

Recapping Y1

Answer 1

• Human sexual dimorphism
  
  • Primary, secondary, and internal characteristics
• Determination of sex
  
  • Genetics, male and female-specific embryonic development under the influence of hormones
• Sexual development
  
  • Puberty, maturation of primary and secondary sexual characteristics, emergence and development of sexual behaviours
• Neural control of sexual behaviour
  
  • Organisational (behavioural masculinisation and behavioural defeminisation) and activational effects (hormone interaction)
• Disorders of sexual differentiation and development
  e.g. Androgen insensitivity syndrome, the case of John/Joan, what these cases tell us about the crucial role of hormones and the brain in determining sexual behaviours

Question 2

Asexual vs sexual reproduction

Answer 2

• Advantages of Sexual Reproduction
  
  • Sexual reproduction mixes genes whereas asexual reproduction relies on mutation alone.
  • Within a species advantageous traits can quickly be bred in (as disadvantageous ones can be bred out). Therefore, more chance for adaptation and survival
• Advantages of asexual reproduction
  
  • All of the parent’s genes are passed on to the next generation (i.e. offspring are clones of parent).
    In a stable population and environment, advantageous as all they need do is survive to reproductive maturity rather than having to compete for a mate.

Question 3

why does sexual dimorphism exist

Answer 3

• It is essentially where feminine and masculine characteristics e.g. males having a larger body size- due to differences in the gametes themselves
• To attract mates
• Due to parental investment
• Sexual dimorphism is crucial for sexual reproduction
• Most obvious sexual dimorphism is the larger body size of males in many vertebrate species
  Difference in male and female gametes (sperm vs ova) – profound effect on vertebrate sexual behaviour

Question 4

how does sexual dimorphism influence behaviour

Answer 4

• Males
  
  • Produce sufficient sperm to inseminate millions of females
  • Less selective – rarely dangerous
• Females
  
  • Nurture their ‘egg investments’ by choosing mate (limited amount)
    Need healthy male

Question 5

parental investment theory

Answer 5

• States that “the relative investment in offspring by males and females is a key variable in sexual selection”
• In most species:
  
  • females invest more in offspring and are the ‘choosier’ sex
  • males invest less and thus compete more over reproductively available females
• In humans:
  
  • Female minimal investment = pregnancy and lactation
    Male minimal investment = fertilization (but greater care = greater chance of survival of progeny i.e. true reproductive success)

Question 6

animal mating systems and reproductive strategies

Answer 6

• Strategies related to differences in investment in offspring.
• PROMISCUITY: animals mate with more than one partner and do not establish long-term relationships.
  
  • This is a common strategy amongst many species
    POLYGAMY: ‘many spouses

Question 7

male-male competition for dominance

Answer 7

• The strongest male ensures:
  
  • In communal groups (herds) almost exclusive access to females (maximise opportunity to pass on genes)
  • In seasonal bonding species, the territory needed to attract females
• Benefits to female:
  
  • Ensures any offspring will be the ‘fittest’ (dominant) i.e. male offspring will be able to pass on her genes)
    Ensures access to resources (i.e. food) meaning offspring most likely to survive to reproduce and pass on her genes

Question 8

human mating systems and reproductive strategies

Answer 8

• Monogamy:
  
  • One male and one female forming a breeding pair
  • Appears to be the norm across most civilisations
  • Promiscuity (especially in women) frowned upon
  • Human infants are frail and need prolonged care
  • Not always permanent
• Critical question: What determines trends in divorce rates?
  
  • Marriage not needed to ensure parental investment?
  • e.g., Child support payments (continued parental investment)?
    ‘Blended’ families becoming more accepted in society (mutually rearing each other’s offspring)?

Question 9

human sexual preferences- evolutionary basis

Answer 9

• Reproductive success is an individual’s production of offspring i.e., how many of our genes are passed on to the next generation
• Natural selection is the process where organisms that are better adapted to their environment have increased survival and go on to produce more offspring
  Sexual selection is natural selection through preference by one sex for certain characteristics in individuals of the other sex

Question 10

human sexual preferences- symmetry

Answer 10

• Facial symmetry has a positive influence on facial attractiveness ratings (Grammer & Thornhill, 1994)
• Facial asymmetry has been related to both environmental and genomic stress (Parsons, 1990)
• Increased asymmetry reflects poorer developmental homeostasis at the molecular, chromosomal and epigenetic levels (Parsons, 1990)
• Faces low in symmetry are rated as more anxious. Supporting that:
  
  • facial symmetry is perceived as being attractive, presumably reflecting health certification
    people also consider facial symmetry as a cue to an individuals’ quality via personality characteristics (Fink et al., 2006)

Question 11

human sexual preferences- skin rednesss

Answer 11

• Skin redness enhanced the perceived health of faces, possibly because of its association with skin blood perfusion and oxygenation and as such good hormonal status
• The role of melanin in the perception of faces is usually considered in terms of skin darkening (‘tanning’)
  Findings were independent of skin texture or colour distribution

Question 12

human sexual preferences- sexually dimorphic traits

Answer 12

• Sexually dimorphic traits suggest underlying hormonal function is optimal
  However, globally results indicate a positive effect of femininity on male assessment of female facial beauty BUT a null or weak effect of masculinity on female evaluation of male facial attractiveness (Kleisner et al., 2024)

Question 13

the menstrual cycle and sexual preferences

Answer 13

• During the periovulatory phase (before ovulation), hormonal levels peak to indicate the release of an egg
• This indicates to the brain that the body is most fertile, and reproduction is an option
  A meta-analysis revealed robust cycle shifts that were specific to women’s preferences for cues of genetic quality (Gildersleeve et al., 2014)

Question 14

sexual preferences

Answer 14

• On a continuum: Exclusive attraction to the opposite sex to exclusive attraction to the same sex
  But in research terms, is generally discussed in relation to these three categories: heterosexual, homosexual and bisexual

Question 15

detecting sexual orientation from facial images

Answer 15

• Wang & Kosinki, 2018
• Can we identify sexual orientation from facial features?
  
  • Gay men and lesbians marginally more accurate than heterosexuals (Brambilla et al 2013)
• Artificial intelligence using ‘deep neural networks’ that learn to recognise patterns in multi-layered data
• Extracted data on facial features from 35,000+ facial images
  
  • Fixed features (e.g. nose shape)
  • Transient features (e.g. grooming style)
• Gay men and women tended to have gender-atypical facial morphology, expression and grooming style
  AI able to correctly distinguish between gay and heterosexual men (81% of cases) and women (71% of cases)w

Question 16

what controls a persons sexual orientation- social explanations

Answer 16

• Bell, Weinberg and Hammersmith (1981)
  
  • Large scale study of several hundred male and female homosexuals
  • No evidence that homosexuals had been raised by domineering mothers or submissive fathers
  • Best predictor of adult homosexuality was a self-report of homosexual feelings
  • Conclusion: Data did not support social explanation for homosexuality but were consistent with biology offering at least a partial explanation
• Yin Xu
  
  • Data on 9,795 youths from UK Millenium Cohort
  • Measures of sexual attraction to males and females at 14 years
  • Findings:
  • Girls with greater maternal psychological distress since age 7 and greater pubertal BMI more likely to be non-heterosexual BUT very small effect sizes
    No significant associations between early life conditions and later sexual orientation in males

Question 17

what controls a persons sexual orientation- interference with prenatal androgenisation

Answer 17

• Maternal stress
• Suppressed androgen production in male foetuses
• Less likely to display male sexual behaviour
• More likely to display female sexual behaviour
• Play behaviour also resembles that of female
• Reduces size of sexually dimorphic nucleus (SDN) in hypothalamus
  In one study (LeVay, 1991) INAH was larger in heterosexual men than homosexuals (not consistently replicated)

Question 18

What controls a persons sexual orientation- biological explanations (prenatal hormones and related physical/behavioural correlates)

Answer 18

• Bogaert & Skorska (2020)
  
  • Refers to role of prenatal hormones in organisational effects on brain
  • Prenatal hormones (e.g., androgens) strongly associated with:
  • Finger digit ratios
  • Otoacoustic emissions (sounds given off by inner ear when responding to sound)
  • These physical correlates more consistently associated with sexual orientation in women than in men
  • Also, homosexual participants had 39% greater odds of being non-right-handed which may be driven by prenatal hormone exposure (Lalumiere et al., 2000)
    Evidence of increased non-righthandedness in men and women who are asexual and bisexual too, suggesting acommon mechanism

Question 19

What controls a persons sexual orientation- biological explanations (fraternal birth order effect, androgenisation)

Answer 19

• Blanchard et al., 2018
  
  • Fraternal birth order (number of older brothers) is reliable correlate of men’s sexual orientation
  • Effect size modest
  • Not found in women
  • Support for mechanism found by Bogaert et al., (2018)
  • Measured antibody reactivity to two male-specific proteins in foetal brain in mothers of gay and heterosexual men
    Mothers of gay sons had significantly higher antibodies to one protein (NLGN4Y) suggesting greater immune reaction against it

Question 20

Biological explanations- prenatal androgenisation via congenital adrenal hyperplasia (CAH)

Answer 20

• Adrenal glands secrete excessive amounts of androgens
• Money, Schwartz and Lewis (1984)
  
  • 30 women with CAH asked to describe sexual orientation
  • 48% = bisexual or homosexual
  • Conclusion: Exposure of a female foetus to excessive androgens does influence sexual orientation
• Meyer-Bahlburg et al. (2008)
  As adults, CAH women have elevated rates of same-sex attraction relative to non-CAH women (but still majority are heterosexual)

Question 21

biological explanations- levels of sex hormones in adults

Answer 21

• Meyer-Bahlburg (1984)
  
  • Levels of sex steroids in male homosexuals are like those of heterosexuals
  • Variations in sex hormones cannot explain male homosexuality
• BUT
  
  • 30% of female homosexuals have elevated levels of testosterone
    Whether differences are related to biological cause or differences in lifestyles increasing release of testosterone is not known

Question 22

biological explanations- genetics

Answer 22

• Ganna et al., 2019
• Heritability studies show greater concordance for same-sex orientation among monozygotic (identical) twins vs dizygotic (fraternal) twins
• However, modest effect sizes and studies with better methodology show lower concordance (Bailey et al., 2016)
• Genetics (chromosomal regions) and epigenetics (expression of genes) studies have found links to sexual orientation but not consistently
• Very large genome-wide association study
• Data suggest likely polygenic trait
• Found five SNP (single nucleotide polymorphisms) loci on five chromosomes associated with sexual orientation
  Limitation: relied on reported sexual behaviour to assess orientation

Question 23

sexual desire

Answer 23

• Santi et al., 2018
• Defined as:
• “A biological process involving steroid hormones acting in the brain of two sexually distinct organisms leveraging on sexual reward”
• Relies on steroid hormones, neurotransmitters, vasoactive agents and other molecules acting through specific receptors, at both the brain and peripheral level
• It is a complex process, involving both cognitive and peripheral physiological mechanisms, leading to sexual arousal
  Sexual arousal = the cerebral activation occurring in both male and female, aiming to prepare genital organs for copulation

Question 24

phases of sexual desire

Answer 24

• Santi et al., 2018
• COGNITIVE PHASE: Sexual stimuli (real interaction or pornographic images etc) – activate cognitive state, appraised and categorized as sexual, neural activity increases in specific cortical areas (slightly different between the sexes).
  PHYSIOLOGICAL PHASE: Changes in cardiovascular and respiratory functions until the genital response (penile blood flow, erection, swelling, female genital lubrication, cervix and uterus elevate to expand vagina).

Question 25

sexual arousal

Answer 25

• Santi et al., 2018
• Driven by hormones which are affected by
  Environmental factors (light and dark), cultural (beliefs about sexual behaviour), psychological (attitudes and cognitions) and relational factors (connection with partner)

Question 26

role of testosterone in males

Answer 26

• Santi et al., 2018
• In animals, positive correlations found between testosterone levels and sperm motility, and negative correlations with fat measurements and ejaculation latency time, revealing the hormone’s impact on reproductive traits
• In humans, also affects sexual desire and cognitive phase of arousal
• Visual sexual stimuli are involved in:
  
  • Sexual
  • Emotional
    Motivational

Question 27

role of testosterone in pre menopausal females

Answer 27

• Santi et al., 2018
• Relationship with sexual arousal is less clear
• Probably because of complexity of endocrine systems in females, and importance of psychological factors in female sexual desire (emotional attachment, pair bonding)
• Anticipation of sexual activity can increase testosterone in females
• BUT hormonal contraceptives can reduce serum testosterone without impairments in sexual interest
• HOWEVER lower testosterone found in breast-feeding mothers complaining of low sexual desire
  May be androgen sensitivity, not level, that is important?

Question 28

the menstrual cycle and sexual desire

Answer 28

• Like with sexual preferences we see cycle-dependent shifts in sexual desire
• Sexual desire is highest in the periovulatory phase
• Interestingly we see shifts in the luteal phase with regards to sexual behaviour
• At this point we see those who perceive their partner as having less interest in the relationship initiating more sexual activity (Grebe et al., 2013)
• Vincent et al., (2022)
  
  • Naturally cycling group:
    ○ the probability of choosing immediate rewards increased from the EF to the LF, followed by a drop again in the LP
  • Hormonal contraceptive group:
    The probability of choosing immediate low-quality sex over delayed high-quality sex seemed to be approximately stable but with an increase toward the end of the menstrual cycle

Question 29

menopause in females

Answer 29

• Menopause is the ceasing of menstruation and fertility in females, usually occurs around age 45-55
• Complex body transition and psychological change
• Bodily changes include:
  
  • Weight, shape, skin, hair, physical symptoms (e.g. bloating, flushes), sexual function
• • 1026 women (40-65 years)
  • Significant factors predicting the physical component summary of HRQoL among middle-aged women included:
  • the orgasm domain, appearance evaluation and menopausal symptoms
  • The factors predicting the mental component summary of HRQoL included:
    ○ the satisfaction domain, appearance evaluation, self-classified weight, relationship with partner, and menopausal symptoms
  • Menopause has significant effect on health-related quality of life so is important to understand (can inform support and treatment)

Question 30

the endocrinology of the menopause

Answer 30

• Schwenkhagen, 2007
• However, reductions in testosterone production from the adrenal glands over menopause is so substantial that even increased production by the ovaries can’t correct the deficit = net loss of circulating testosterone

Question 31

effects of lowered testosterone on sexual behaviour

Answer 31

• Typically, the symptoms of androgen insufficiency include reductions in the following:
  
  • sexual motivation, sexual fantasies, sexual enjoyment, sexual arousal, vaginal lubrication, vasocongestion, pubic hair, bone mass, muscle mass, and quality of life
• What is known is largely based on symptoms of women who are androgen-deficient because of other reasons
  
  • e.g., they have lost their ovaries due to surgery, chemotherapy, or radiation therapy
• • Thirty-five trials (total of 4768 participants) included in the review
  • Adding testosterone to HT has a beneficial effect on sexual function in post-menopausal women
    However, the combined therapy (HT + testosterone) associated with a higher incidence of negative side effects e.g., hair growth and acne- Typically, the symptoms of androgen insufficiency include reductions in the following:
  • sexual motivation, sexual fantasies, sexual enjoyment, sexual arousal, vaginal lubrication, vasocongestion, pubic hair, bone mass, muscle mass, and quality of life
• What is known is largely based on symptoms of women who are androgen-deficient because of other reasons
  
  • e.g., they have lost their ovaries due to surgery, chemotherapy, or radiation therapy
• • Thirty-five trials (total of 4768 participants) included in the review
  • Adding testosterone to HT has a beneficial effect on sexual function in post-menopausal women
    However, the combined therapy (HT + testosterone) associated with a higher incidence of negative side effects e.g., hair growth and acne

Question 32

changes in sexual behaviour after menopause

Answer 32

• Thornton et al., 2015
• 76% of middle-aged women reported that sex was moderately or extremely important to them
• Sexual activity and function decline with age
• Significant decline (74% - 56%, p< 0.001) in sexual activity reported between early postmenopausal women and late postmenopausal women
  Sexual dysfunction also increased from 42% to 88%

Question 33

testosterone decline in males

Answer 33

• Males experience testosterone decline in later life
• Low serum free testosterone levels are associated with long-term and current depressive symptoms and a decreased sexual desire in middle-aged men (Hintikka et al., 2009)
• Low levels are also associated with sexual dysfunction
• Allan et al. (2008)
  
  • Double-blinded protocol to transdermal testosterone patches or placebo for 12 months
  • In men receiving testosterone replacement therapy, testosterone levels increased by 30% (p=0.01)
  • Testosterone therapy subsequently improved sexual desire (p=0.04);
    However other parameters of sexual function including erectile function were unaffected by the treatment

Question 34

orgasms

Answer 34

• Orgasm: A series of muscle contractions in the genital region that is accompanied by sudden release of endorphins.
  Orgasm normally accompanies male ejaculation as a result of sexual stimulation, and it also occurs in females as a result of sexual stimulationw

Question 35

what happens during an orgasm?

Answer 35

• Regarding orgasm the two clear differences between men and women are that:
• Dopamine increases with orgasm AND larger effect for females.
• Adrenaline correlated with premature ejaculation for men BUT increases orgasm pleasure for females.
• The female orgasm is correlated more strongly with oxytocin than male orgasm.
  Could this have an evolutionary basis as it is more important for a female to have higher oxytocin during copulation in order to bond with their mate and potential co-parent?

Question 36

male brain during an orgasm

Answer 36

• Holstege et al. (2003)
• Eleven healthy right-handed heterosexual male volunteers
• The volunteers were asked to perform the following tasks twice:
  
  • rest, erection, sexual stimulation, and ejaculation induced by sexual stimulation.
• To minimize motor activity by the volunteer during the scan, sexual stimulation was provided by his female partner by means of manual penile stimulation in the tasks stimulation and ejaculation.
• The volunteer’s head was maintained in position with a head-restraining adhesive band, and, to minimize visual input, volunteers were asked to keep their eyes closed.
• Participants had to practice during the week beforehand.
• The most prominent activation was found in large portions of the cerebellum during ejaculation.
  
  • It is possible that this activity represents movements made by the volunteers during ejaculation, although these movements were relatively limited.
  • The cerebellum, however, is not only involved in motor but also in emotional processing
• There was also activation of the secondary visual cortex which seems surprising, because the volunteers had their eyes closed.
  
  • This activation might be explained, however, by the volunteers using visual imagery during the experiments.
• Deactivations in amygdala and entorhinal cortex.
  Likely due to reduced fear during ejaculation.

Question 37

female brain during an orgasm

Answer 37

• Wise et al. (2017)
• 14 ‘highly orgasmic’ participants.
• Self stimulation vs. partner stimulation.
• 4 phases:
  
  • Early, Late, Orgasm, Recovery
• They no significant difference between groups for any brain regions during orgasm

Question 38

why females orgasm

Answer 38

• Evolutionarily…Pavličev and Wagner (2016) found that as ovulation stopped depending on orgasm (as seen in other mammals), the clitoris stopped being located inside the vaginal canal.
• Oxytocin and bonding?
• They feel good, encouraging sexual intercourse?
• Female orgasms are important for reproduction too!
• Fewer sperm in the post-coital “flowback” of women who had orgasms versus those who did not.
• Uterine contractions are the primary method of sperm transportation. These contractions move sperm not only into the uterus, but laterally, toward the more mature ovarian follicle, and women who are better at doing this are more likely to get pregnant.
  
  • When an orgasm occurs, there are uterine contractions!
    Pair this with research showing that uterine contractions intensify during the oxytocin release triggered by orgasm, and you have compelling evidence that the female orgasm, while certainly not necessary, can play a role in fertilization (Komisaruk & Whipple, 2005).

Question 39

orgasm research

Answer 39

• Measuring blood hormone levels:
  
  • cannot measure during orgasm.
  • blood samples can create fear response (which is not conducive to orgasm).
• Measuring brain activity:
  
  • extremely difficult to control the stages of orgasm.
  • limiting movement during orgasm.
• Contextual issues:
  
  • any circumstance outside of ‘natural’ sexual activity may not represent the ‘natural’ orgasm experience.
    those who take part are self-selected and may not represent the average person.

Question 40

benefits of an orgasm

Answer 40

• Good for your heart
  
  • Sexual arousal sends the heart rate higher, and the number of beats per minute reaches its peak during orgasm.
  • BUT unless you’re having 150 minutes of orgasms a week, try cycling, brisk walking or dancing.
• Fertility
  
  • Fewer sperm in the post-coital “flowback” of females who have orgasms versus those who do not.
• Stress
  
  • Plenty of people find that intimacy or orgasm without penetration helps them feel relaxed, as do exercise or meditation. It does not have to be penetrative sex – it is whatever works for you
• Brody (2010) – a review of relative health benefits of different sexual activities found:
  
  • Females who had orgasm solely through intercourse were more satisfied with their mental health than females who had only experienced orgasms through direct clitoral stimulation.
    Orgasmic frequency correlated with relationship satisfaction.

Question 41

orgasms when older

Answer 41

(Jarzabek-Bielecka et al., 2012)
- Maintaining a level of sexual activity means the biological changes associated with aging less pronounced.
- Some other benefits include:
- Sex burns fat and causes the brain to release endorphins, that act as painkillers and reduce anxiety.
- In men, sex stimulates the release of growth hormones and testosterone, which strengthen bones and muscles.
- Sex also seems to prompt the release of substances that bolster the immune system.
- Some studies suggest that sex (performed about three times a week) can slow aging and prevent wrinkles around the eyes from appearing.
Continuing to have sex will preserve sexual vigor beyond middle age. Sexually active people have higher levels of naturally produced sex hormones.

Question 42

orgasms when older (females)

Answer 42

• While oestrogen production decreases, especially after menopause, it alters the thickness and size of a woman’s reproductive organs. These changes include:
  
  • loss of elasticity and thinning of the vaginal tissue.
  • decrease in the amount of lubrication.
  • decrease in the size of the clitoral, vulvar and labial tissues.
  • decrease in the size of the cervix, uterus and ovaries.
• These changes alter the experience of sex in the following ways:
  
  • the anticipation before orgasm decreases.
  • orgasms may be less intense.
  • sexual desire may be reduced.
  • Vaginal discomfort, dryness or pain during intercourse may occur, due to decreased lubrication.
• As they age, women require more time to become sexually aroused, take longer to lubricate, produce less vaginal lubrication, have less intense orgasms, and need more clitoral stimulation to become orgasmic.
• The ability to have orgasms does not change significantly with aging, but older women are less likely to be multi-orgasmic. Also, the number of vaginal contractions decrease.
• Women who are coitally active after menopause have less vulvar and vaginal atrophy and higher levels of androgen than abstinent women.
  A diversity of complex controlling factors as well as an abundance of ways in which human sexuality is expressed remains an important methodological problem which impedes a scientific description of the phenomenon in question.