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Flashcards in Reproductive behaviour Deck (17)
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reproductive behav

Sexual selection
- Preferential reproduction in some indv which changes traits that get represented in popn - leads to:

Sexual dimorphism
- Diff between males and females

All organisms evolved to reproduce


early development

Primary sexual characteristics – i.e. internal and external genitalia.

Sry gene causes male internal genitalia - testes.

No Sry gene causes female internal genitalia - ovaries.

Hormones from testes have an organisational effect promoting masculinisation and defeminisaton.

Initially foetuses identical other than genes

Sry gene within Y chromosome

Females = absence of hormones – default

Males are slightly modified female

see notes


hypothalamus - arcuate nucleus

Puberty is initiated by the arcuate nucleus of the hypothalamus – time-keeper for initiation of puberty

kisspeptin causes the anterior hypothalamus to release Gonadotropin-releasing hormone (GnRH).

see notes


pituitary - GnRH

GnRH causes pituitary to release FSH and LH in both sexes.

FSH and LH cause testes to release testosterone and ovaries to release estradiol.

These hormones drives the development of sexual maturation.

see notes


hypothalamus and pituitary - master endocrine system

Hypothalamus and pituitary are the master controllers of the endocrine system.

Communicate via hormones in the blood releases into circle of Willis.

Play an organisational and activational role.

Optimal position to release hormones into bloodstream

see notes


hormonal control of sexual behav

Hormonal control of the menstrual cycle.

The combination of estradiol + progesterone and signals the fertile phase of the female’s cycle.

The combination of E+P promotes sexual behaviour in females

Fertile = produce progesterone and estradiol – promotes sexual behaviour


rat sexual behav

Rats show species specific sexual behaviour sequences (humans are a bit more variable).
- Proceptivity – female approach
- Attractiveness – male engagement/mounting
- Receptivity – female willingness
- Lordos – female posture


hormonal control of sexual behav

The Interaction between activational and organization effects is revealed by a series of experiments.

Males and Females are gonadectomised at birth and either given hormones at that time (to study organisational effect) or in adulthood (to study activational effects) – brain cannot develop in same way

Table shows that gonadectomised males need replacement hormones at birth in order to show activational effects in adulthood.

see notes

Organisational = need hormone when developing in order to have substrate that makes you sensitive to activational effect of hormones when post-puberty – actually have effect on behav

Need testosterone at birth to have organisational effect

Testosterone defeminises brain


human sexual behav

Females are more attractive when they are in the fertile (luteal) phase (progesterone+estradiol).

Raters of both sexes rated the attractiveness of female pictures taken during the follicular and luteal (fertile phase).

Circa 5% preference for fertile females

see notes

Is the data robust?

Initiation of sexual activity between human partners.

Males initiate sex evenly across the female menstrual cycle.

Females initiate sex more often during ovulation (the fertile phase)

see notes

Previous research doesn’t converge into more initiation by males in the fertile phase

What do females prefer in men when they are fertile vs. non-fertile?

Rate qualities as a one-off sexual partner

They show a greater discrimination in their preference for signals of male dominance and genetic quality/compatibility.

MHC = Major histocompatibility complex – mis-match between immune systems between 2 genders

see slides


male sexual behav - Bagatell et al. (1994)

Male administration of a GnRH antagonist (Nal-Glu) blocks testosterone production and sexual behaviour in males, but not if given replacement T

see slides

Reduced freq of sexual desire, intercourse, fantasies and masturbation with antagonist alone – losing testosterone


sexual orientation

Male heterosexual = brain masculinized and defeminized

Female heterosexual = neither masculinized nor defeminized – left alone – default

Male homosexual = neither masculinized nor defeminized

Female homosexual = brain masculinized and defeminized

Male and female bisexual = masculinized but not defeminized.

physical morphology

congenital adrenal hyperplasia (CAH)

androgen insensitivity syndrome



physical morphology - Balthazart (2016)

Individuals who prefer woman (heterosexual males and lesbians) have been masculinised and defeminised, and have a masculine index to ring finger ratio (and longer limbs).

Individuals who prefer males (heterosexual woman and homosexual men) have been feminized and have a feminine index to ring finger ratio (and short limbs).



Abnormal androgens in genetic females.

Produces ambiguous genitalia.

≈33.3% genetic females with CAH identify as homosexual or bisexual compared to ≈2% of females as a whole.


androgen insensitivity syndrome

Testosterone should masculinisation and defeminise morphology.

Genetic males with androgen insensitivity syndrome develop as females.

They may be complete or partial females depending on the level of insensitivity.

Typically female external genitalia, but also with testes (internal) and without uterus or Fallopian tubes.

Typically favour male partners as do heterosexual females, suggesting neural feminisation.



Estimates of concordance rates for homosexuality in male and female identical twins and fraternal twins.

Suggest that there is a genetic influence on homosexuality.

However, if homosexuality was was perfectly heritable, the concordance rates for identical twins should be 100%.

50% role for psychosocial learning – less well understood

see notes


neural basis of male sexual behav - Balthazart (2016)

What differences are there in the male vs. female brain which are responsible for male sexual behaviour?

Animals: Sexually dimorphic nucleus of the medial preoptic area MPA of the hypothalamus.

Humans: interstitial nucleus of the anterior hypothalamus number 3 INAH3.

The INAH3 is the human homologue of the MPA.

see slides

Human INAH3
- Post mortem examination indicates that the INAH3 is 2-3 times larger and has a higher cell density in heterosexual males than homosexual males and females.
- Closed circles = died from AIDS.
- No difference in heterosexual men with and without AIDS, suggesting this did not cause the INAH3 differences.
- Confound = homosexuality and dying of aids correlation high – reduction could be due to age related dementia/aids

see notes

see big card


neural basis of female sexual behav

see big card