Lecture 6 Flashcards
(27 cards)
Sexual Behavior
Gender Traits Libido Sexual Orientation Gender Identity Attraction/Mate Selection Mate Bonding Monogamy vs Polygamy Receptivity
Behavioral Traits are Extremely Diverse Across the Human Population
They are the result of interactions among a suite of factors that include biology, experience, and context.
GRAPH
Gender TraitsMasculine vs Feminine
Nature hypothesis
The exposure of the non-sexual brain to steroid hormones at a Critical Period during gestation & perhaps following birth, organizes into masculine or feminine variants, specific regions of the brain responsible for sexual behavior.
Nurture hypothesis
Humans are taught, implicitly and explicitly, to behave in a manner appropriate to their biological sex.
Gender Traits
It is currently accepted that the ‘either nature or nurture’ dichotomy is false.
In actuality,
both steroid hormones and socialization interact to determine and modify gender traits
masculine and feminine traits are not always associated or correlated with biological anatomy
Bottom Line: In any individual, biology and culture interplay to give rise to gender traits.
Libido: conscious or unconscious sexual desire
Male sexual drive:
androgens within a defined range are necessary but not sufficient (androgen levels required are below that necessary to maintain spermatogenesis)
evidence suggests that certain brain traits that are androgen-independent are required
Female sexual drive:
no ovarian hormones are correlated to sexual drive but tonic levels of androgens may be needed
‘psycho-social factors’ may dominate any hormonal influence, particularly in younger females
Testosterone Production by Age in Males & Females
GRAPH
Puberty & First Arousal
GRAPH(2)
Sexual Orientation
Heterosexuality or Gender Typical Partner Choice: choosing to sexually interact with partners of the opposite sex
Homosexuality or Gender Atypical Partner Choice: choosing to sexually interact with partners of the same sex
Question that often arises: Does it have a biological basis?
Finding a biological basis has been difficult and may be due to limited scientific studies in this area. Also, there are probably multiple biologic factors involved.
Many ask: Why is it important to find a biological basis?
Sexual OrientationEvidence for Biological Basis
Hormone Comparisons
No differences have been found in hormone levels between heterosexuals and homosexuals.
Brain Anatomy
Studies claiming to find brain differences in women and homosexual men when compared to heterosexual men have been debunked. A causal correlation between brain anatomy/function and homosexuality has not been unequivocally demonstrated.
Sexual OrientationEvidence for Biological Basis cont.
Genetic Differences
Two Studies
1993 (Hamer): found DNA ‘markers’ on the X-chromosomes (Xq28) of homosexual brothers (40 pairs).
2014 (Sanders): found DNA ‘markers’ on the X-chromosome (Xq28) and chromosome 8 (8q12) of homosexual brothers (409 pairs).
Behavioral and Molecular Genetics
Family and Twin Studies
Homosexuality is increased among relatives of homosexuals
Elevated maternal line inheritance (homosexual maternal uncles)
Both suggest chromosomal – autosomal- or X-Chromosome-linked, respectively
Twin Studies – If one twin is homosexual, what is the probability that the other (same sex) will be?
GRAPH
Fraternal Birth Order EffectFBO
For males, number of older brothers (gay or not) increases chances of being homosexual by 33% for each older brother
Estimated that 1:7 homosexual males may be due to FBO
Epigenetic Effect Hypothesis
to explain homosexuals in families with no genetic effect identified…
EPIGENETICS: chemical signals on DNA that control which genes are read and how much
These chemical signals are inherited from parents
PROPOSE epigenetic effect acting on how cells respond to androgen signaling in the brain: steering opposite effects in males and females, i.e. driving each toward opposite brain effects
PROBLEM:unreliable data so far
Gender Identity: the sense of being male or female
No physiological parameters of gender identity have been identified.
Studies depend on what people say about themselves.
Is gender a discrete property with just two possibilities (male or female) or is there a continuum of gender identities?
Does gender occur at multiple biological, anatomical, physiological and psychological levels?
Sexual AttractionMate Selection
Attraction between males and females is culturally influenced and dependent upon
visual cues
auditory cues
olfactory cues
other chemical cues
The first two are most often studied in a psychological context, but the third intrigues biologists.
Pheromones
chemical compounds released by one individual that elicit a physiological response in another individual
Human sensory systems
Sources of human pheromones
Roles of pheromones
Human Sensory Systems
Main Olfactory System (MOS)
olfactory receptors in the nasal cavity detect odorous compounds
signals are sent to higher brain centers so perception is conscious
Accessory Olfactory System (AOS)
receptors in the floor of the nasal region detect compounds that may have no odor (vomeronasal organ or VNO)
signals are sent directly to hypothalamus, bypassing higher brain centers, so no cognitive perception
Probable Source of Human Pheromones
Apocrine Glands
mature at puberty
secrete odorless substance
bipedal human stance may accentuate the distribution of substances
Possible and Putative Effects of Pheromones
Sexual attraction between males and females.
Control of female monthly cycles.
presence of males
Infant-mother bond in early postnatal period.
Sexual Attraction/Mate SelectionOther Chemical CuesMajor Histocompatibility Complex (MHC)
The MHC is a multigene family that codes for key receptor molecules that recognize and bind foreign proteins for presentation to specialized immune cells which initiate an immune response.
Humans have been shown (when not distracted by artificial odors) to choose partners with a high degree of variability from their own MHC, thus insuring immune systems in offspring with wider capabilities of recognizing foreign substances.
Stages of Mate Bonding
Lust – novelty of early attraction and sexual interaction stimulates dopamine release, which acts as a natural opiate, increasing feelings of intense energy, exhilaration, focused attention and motivation. Low serotonin (similar to depressive conditions) promotes ‘obsessive’ love.
Romantic Love – increased tolerance of dopamine reduces the initial ‘drugged’ feeling, but feelings of long term bonding and closeness are supported by oxytocin. Oxytocin levels are maintained by making love orgasms with your partner hugging your partner massaging each other
Attachment – long term maintenance by high levels of oxytocin.
Monogamy vs Polygamy
Polyandry vs Polygyny
Polygyny = males have more than one female mate Polyandry = females have more than one male mate
Our Clostest relatives
Our closest relatives are the Chimpanzees and the Bonobos (pygmy chimps)
We share from 98 to 99% of our genes with them.
BUT, which genes do we share??
Info about Chimpanzees
In Chimpanzees ♂♂ are dominant and choose with whom they will mate. One ♂ is dominant & fights off other ♂ ♂ of the community to keep ♀ ♀ to himself.
When ♀ ♀ reach maturity, they leave to find another community.
Disputes over food, mates, territory, etc. are settled by aggression and fighting.
Sometimes, community members leave their territory to attack other communities.
