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.