Week 9-Sexual Behaviour Flashcards
Give a recap of year 1
-Human sexual dimorphism: Primary=genitalia/Secondary=puberty e.g., hair growth, breast development etc.,/and internal characteristics
-Determination of sex: Genetics, make 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
What are the advantages of Sexual Reproduction?
-Sexual reproduction mixes genes whereas asexual reproduction relies on mutation alone
-Within a species advantageous traits can be quickly bred in (as disadvantageous ones can be bred out.). Therefore more chance for adaptation
-Dimorphism is needed for sexual reproduction
-Sexual reproduction can breed out anything problematic to be adaptive
What are the 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 to do is survive to reproductive maturity rather than having to compete for a mate
-Asexual reproduction no risk in a mate (although if issue in one mate then whole line is wiped out)
What is Sexual Dimorphism?
-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) - has a profound effect on vertebrate sexual behaviour
-Sperm that is larger or more nutrient based is selected for meaning larger sex cells making chance of successful offspring greater
-Sperm that is smaller may be beneficial as causes less harm to holder as long as big nutrient filled sex cells (ova) present to pair with (and this affects how be behave sexually)
How does dimorphism influence sexual behaviour in regards to male gametes?
Male gametes are small and cheap
-Cheap is in regard to not much cost to produce much sperm with bare minimum in materials to generate offspring
How does dimorphism influence sexual behaviour in males and females?
Principles apply to most mammals
Males:
-Produce sufficient sperm to inseminate millions of females
-Less selective - rarely dangerous
Females:
-Nurtures their ‘egg investments’ by choosing a mate
-Needs a healthy male
-Egg investments=packing lots of nutrients into the egg so would be a waste if it wasn’t a viable offspring (born with all the eggs we will ever have so limited number unlike males)
What is the Parental Investment Theory? (Marzoli et al., 2018)
-Purports that the “relative investment in offspring by males and females is a key variable in sexual selection.”
In most species (excluding seahorses):
-Females invest more in offspring and are the choosier sex
-Males invest less and compete more over reproductively available females
In humans:
-Female minimal investment = pregnancy and lactation
-Lactation relates to breast-feeding biologically whether women choose to do so or not
-Male minimal investment: fertilisation (but greater care = greater chance of survival of progeny i.e., true reproductive success) (so can leave whenever essentially)
-This builds on the investment from the gametes in the sex cells
What some issues with this topic as a whole?
-Doesn’t account for homosexual relationships
-Not everyone has sex for reproduction purposes
-Fertility issues
What are 2 animal mating systems & strategies?
Strategies related to differences in investment in offspring
1. Promiscuity: animals mate with more than one partner and do not establish long-term relationships
- Polygamy: ‘many spouses’
Common feature of animal kingdom is adopting male/female promiscuity as a reproductive strategy:
-Being promiscuous as a male is deemed a logical on a biological basis especially related to investment terms
-Dominant males will be promiscuous
What does the strongest male ensure?
-In communal groups (herds), almost exclusive access to females (to maximise the opportunity to pass on genes)
-In seasonal bonding species, the territory needed to attract females
-Will have alpha male in herd who will dominate territory offering female access to things such as food, shelter, genetically strong parent (i.e., healthy) etc., and also gets first dibs
How is the strongest male a benefit to females?
-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
Human mating systems & reproductive strategies: What is Monogamy?
-One male and one female form a breeding pair
-Appears to be the norm across all civilisations
-Promiscuity (especially in women) frowned upon
-Human infants are frail and need prolonged care
-Not always permanent i.e., divorce
What are some key terms in natural & sexual selection?
- Reproductive success-How many copies of our genes pass on to the future generations
- Adaptations-Heritable traits that increase long-life reproductive success
- Natural selection-Forces that drive survival and reproduction
- Sexual selection-operates via mating preferences
-To understand sexuality well it’s important to have an evolutionary basis (what about homosexuality?)
Give an example of attractiveness of cues to health: Symmetry (Grammer & Thornhill, 1994; Parsons, 1990)
-Men and women prefer symmetry and viewed them as more pretty/attractive
-Symmetry is a cue to good genes
Give an example of attractiveness of cues to relatedness: Skin pigmentation (Stephen et al., 2009)
-Healthy skin tone indicates how efficiently our body transports oxygen in the blood
-Diet can influence pigmentation
-Skin tone indicates the somatic state of an individual (i.e., health)
Give an example of attractiveness of cues to ‘Good Genes’ & Fertility: Sexual Dimorphism (Burris et al., 2014)
-Pictures modified to be more masculine and more feminine
-Levels is influenced by levels of circulating hormones (more feminine=seen with greater fertility)
-Testosterone levels can either positive or negative outcomes
-More testosterone=more masculine=greater protection Yet cost is lower stability in long-term relationships (opposite seen in lower testosterone levels)
How does the Peri-Ovulatory shifts affect preference?
-Depiction of one menstrual cycle
-First hormone is sex hormones
-Theorised that during ovulation phase, preferences shift as conception risk is high (would want someone more masculine e.g., symmetrical then in lower conception phases, prefer lower masculinity for long-term stability). Therefore they direct their attention to cues of good genes (e.g., masculinity, muscularity, symmetry) (Gangestad & Thornhill, 1998)
Is the evidence towards Peri-Ovulatory shifts reliable?
-Two Meta-analyses with conflicting results (Gildersleeve et al., 2014; Wood et al., 2014)
-Could have been a strong publication bias in top one (Gangestad’s one?)
What is missing with research in Peri-Ovulatory shifts?
-It’s more complicated than expected
-Common signalling for neuro-endocrine-behaviour axis is still missing
-We don’t know if it’s the follicles, ovaries etc., signalling something in the brain
What is Sexual Orientation on a continuum?
Exclusive attraction to the opposite sex———-Exclusive attraction to the same sex
But in research terms, it’s generally discussed in relation to these 3 categories (Roselli, 2017):
1. Heterosexual
2. Homosexual
3. Bisexual
Can we identify sexual orientation from facial features? What evidence is there?
-Gay men and lesbians marginally more accurate than heterosexuals (Brambilla et al., 2013)
Wang & Kosinski (2018):
-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 as you’d expect this to be different in different sexualities)
-Gay men and women tended to have gender-atypical facial morphology, expression and grooming style
-AI was able to correctly distinguish between gay and heterosexual men (81% of cases) and women (71% of cases)
-Suggests there are biological processes underpinning the facial morphology with a common origin somewhere
What 2 explanations have been used to explain what controls a person’s sexual orientation?
- Social explanations
- Biological explanations
Nature vs Nurture essentially
What did Bell, Weinburg & Hammersmith (1981) find when investigating social explanations for sexual orientation?
-Large scale study of several hundred male and female homosexuals
-No evidence that homosexuals had by raised by domineering mothers or submissive fathers
-Argument is that these type of parents are the opposite of what is ‘typical’ is what moulds child to be gay
-Best-predictor of adult homosexuality was a self-report of homosexual feelings
Conclusion: Data did not support social explanations for homosexuality, but were consistent with biology offering at least a partial explanation
-Genes that kick in primary and secondary characteristics, perhaps is kicks in sexual feelings too
What did Xu, Norton & Rahman (2020) find when investigating social explanations for sexual orientation?
-Data on 9795 youths from UK Millenium Cohort.
-Examined family makeup
-Measures of sexual attraction to males and females at 14 years.
-Girls with greater maternal psychological distress since age 7 and greater pubertal BMI were more likely to be non-heterosexual BUT very small effect sizes.
-If sample size was smaller perhaps it would have no effect size at all
-No significant associations between early life conditions and later sexual orientation in males.
Biological Explanations: How does Maternal Stress interfere with prenatal androgenisation and how does this affect sexual orientation?
-Presence of stress interferes with androgen in male foetuses
-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 females
-Reduces size of sexually dimorphic nucleus (SDN)
-In one study (LeVay, 1991) INAH was larger in heterosexual men than homosexuals (not consistently replicated). INAH=Inter-nucleus anterior hypothalamus
Biological Explanations: How can Prenatal hormones and related physical/behavioural correlates with sexual orientation? (Bogaert & Skorska, 2020)
-Refers to the role of prenatal hormones in organisational effects on the brain
Prenatal hormones e.g., androgens strongly:
-Finger digit ratios (Relative size of your index finger to your ring finger)
-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 common mechanism
-More clear cut in women than in men
-Same hormones might be affecting both the same things at the same time
Biological explanations Prenatal androgenisation: How does the fraternal birth order effect sexual orientation?
Blanchard et al., (2018):
-Fraternal birth order (number of older brothers) is reliable correlate of men’s sexual orientation
-Effect size is modest
-Not found in women
-More older brothers=less likely to be homosexual
How can the Maternal immune response play a role in the fraternal birth order effect and sexual orientation?
-Mother’s pregnancy of male foetus = production of antibodies to protein’s for male brain development
-More pregnancies = greater concentration of antibodies
-Mother does not need hormones which are recognised as alien in her body
-Mother produces antibodies against those hormones so it’s not impacting her body i.e., making her more masculine
-Getting to 2nd/4th son, greater build up of those antibodies meaning more masculine hormones destroyed
Support for mechanism found by Bogaert et al., (2018):
-Measured antibody reactivity to 2 male-specific proteins in fetal brain in mothers of gay and heterosexual men.
-Mothers of gay sons had a sig. higher antibodies to one protein (NLGN4Y) suggesting greater immune reaction against it.
Biological explanations exploring prenatal androgenisation: How does Congenital adrenal hyperplasia (CAH) play a role in sexual orientation?
-Adrenal glands secrete excessive amounts of androgens
Money, Schwartz & 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 elevanted rates of same-sex attraction relative to non-CAH women (but still majority are heterosexual)
-Money was involved in David Reiner case (i.e., John case)
-Much higher rate than you’d expect due to general prevalence of homosexuality in the world
How does the levels of sex hormones in adulthood play a role in sexual orientation? Meyer-Bahlburg (1984)
-Levels of sex steroids in male homosexuals are similar to 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 causes or differences in lifestyles increasing release of testosterone is not known
-Some women naturally have more testosterone without a disorder meaning greater chance of being homosexual
How does genetics/heredity play a role in sexual orientation?
-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
-Monozygotic=One zygote
-Share same environment but MZ twins have identical genes so can distinguish level genes play a role
What was found when a very large genome-wide association study was conducted?
-Data suggested likely polygenic trait
-Found 5 SNP (single nucleotide polymorphisms) loci on 5 chromosomes associated with sexual orientation
-May not be one singular gene in sexuality but several
-Limitation: relied on reported sexual behaviour to assess orientation
-Asked whether they have partaken in sexual behaviour with the same sex
-Some may have had feelings of attraction but only explored with one sex (which wasn’t often accounted for)
What is sexual desire? Santi et al., 2018
-“A biological process involving steroid hormones acting in the brain of 2 sexually distinct organisms leveraging on sexual reward.”
-Desire is the process before the end point aka arousal
-Relies on steroid hormones, NTs, 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 occuring in both male and female, aiming to prepare genital organs for copulation
What are the 2 main phases of Sexual Desire? Santi et al., (2018)
- Cognitive phase: Sexual stimuli (real interaction or pornographic images etc.,) -activates the cognitive state, appraised and categorised 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 elevates to expand the vagina).
-Both phases differ in men and women
-Suggests women would need a greater emotional connection
What is sexual arousal driven by? 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).
What is the role of testosterone in males? Santi et al., 2018
-In animals, positive correlations found between testosterone levels and sperm motility (how agile the sperm is), 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:
-Sexual
-Emotional
-Motivational arousals which modulate the activity of specific brain regions
What’s the role of testosterone in pre-menopausal females? 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?
-Anticipation example can be waiting for a date
-Lower sexual desire can be due to greater focus on child care
-Not always due to the presence or production of a hormone, but more how the body responds to it
What is menopause?
-Ceasing of menstruation and fertility in females, usually occurs around 45-55y
-Complex body transition and psychological change
Bodily changes include:
-Weight, shape, skin, hair, physical symptoms (e.g., bloating, flushes), sexual function
-1 year absence of menstruation before it classes fully as menopause
What did Chang, Yang & Chen (2019) find with menopause?
-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 HRQoL included:
-The satisfaction domain, appearance evaluation, self-classified weight, relationship with partner, and menopausal symptoms
-The menopause has significant effect on health-related quality of life so is important to understand (can inform support and treatment)
-Cross-sectional survey
-Menopausal symptoms were important in driving the physical and emotional aspects in the quality of life
What is the endocrinology of the menopause? Schwenkhagen (2007)
Decline in follicular functioning:
-Decreased: Estradiol + Inhibin
-Increased: FSH
-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
-Inhibin normally inhibits the FSH so if it decreases, it loses the suppression effect, causing a corresponding increase in the follicle-stimulating hormones (aka FSH)
What is the effects of lowered testosterone on sexual behaviour? Schwenkhagen (2007)
-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
-Typically, 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
-Vasocongestion= the swelling of bodily tissues caused by increased vascular blood flow and a localized increase in blood pressure
What did Sombooporn, Bell & Davis (2005) find in their review of testosterone for peri and postmenopausal women?
-35 trials (total of 4768 participants) included in the review
-Adding testosterone to HT has a beneficial effect on sexual function in the post-menopausal women
-However, the combined therapy (HT + testosterone associated with a higher incidence of hair growth and acne and a reduction in HDL cholesterol
What did Thornton, Chervenak & Neal-Perry (2015) find when researching changes in sexual behaviour after menopause?
-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%
-Hormonal, physiological and social changes
