
Why do we have particular preferences?
◦ Evolutionary Explanations

Sex differences? Psychoneuroendocrinology

Preferences/behaviors and choices…..
1871 – evolution of characteristics that
give organisms a reproductive
advantage
“Survival of the fittest” –
definition of survival

Sexual selection based on parental
investment by each sex
◦ kin selection
 certain wasp species; certain bird species

E.O. Wilson


The sex that invests more in offspring should
be more choosy or discriminating
The sex that invests less in offspring should
compete more vigorously for opposite sex

amount of time for a woman –

amount of time for a man -

females

males


always use posthoc observations to explain
behavior
never can be really proven


“The Evolution of Desire: Strategies of
Human Mating”
has looked at preferences across MANY
cultures from around the world with specific
predictions……..

Hypothesis: Men will express greater desire
for, or interest in, short-term mates than
women
n= 148 college students; 75 men, 73 women
Asked if seeking short-term mate (“ one
night stand, brief affair) and independently
whether they were seeking a long-term
mate (defined as marrige partner)
7 point scale
1 – not at all currently seeking
7 – strongly currently seeking

For any given period of time, men will desire
a larger number of mates than will women
From Buss and Schmitt, 1993

Which sex would more likely consent to
sexual intercourse after knowing the other for
a shorter period of time?
From Buss and Schmitt, 1993

Attractive confederate approaches
students on University of Hawaii campus
“I have been noticing you around campus, I find
you very attractive”…..
a. Would you go out with me tonight?
b. Would you come over to my apartment tonight?
c. Would you go to bed with me tonight?

Importance of financial prospects

Age of partner

What is a hormone?
◦ chemical substance released that binds to receptors
on other cells

How is this different from a neurotransmitter?
Some chemicals act as both neurotransmitters
AND hormones

What is a hormone?
◦ chemical substance released that binds to receptors
on other cells

How is this different from a neurotransmitter?
◦ travels further distance
◦ released by glands



critical for aspects of sexual behavior (and
development of sex organs and circuits)
ex. estrogen, testosterone,
these are lipid (fat) soluble and readily cross
membranes and so can even bind to
receptors in neuronal and cell nuclei
1.
organizational effects
•
critical window for organizational effects (usually
early in development)
1.
organizational effects
•
critical window for organizational effects


effects are usually permanent
primary sexual characteristics
• structural AND CNS circuitry
2.
Activational Effects
•
•
•
activating established circuits
effects are reversible and usually occur after
puberty
secondary sexual characteristics

genotypic sex vs phenotypic sex
◦ genotypic sex - determined at time of
fertilization
23rd chromosome is sex chromosome

phenotypic sex –
◦ what you see………

Y chromosome controls development of
gonads
gonads – sex organs that releases steroid
hormones (for males; testes for females;
ovaries)

on Y chromosome is a gene - HY antigen

◦ if present- testes will develop ~ 6 weeks after
conception



Y chromosome controls development of gonads
gonads – sex organs that releases steroid
hormones (for males; testes for females; ovaries)
on Y chromosome protein is producedHY antigen
◦ if present testes will develop ~ 6 weeks after
conception
◦ if not present – ovaries will develop



Y chromosome controls development of gonads
gonads – sex organs that releases steroid
hormones (for males; testes for females; ovaries)
on Y chromosome is a gene antigen
HY
◦ if present testes will develop ~ 6 weeks after
conception
◦ if not present – ovaries will develop
◦ up until that time a single “premordial” tissue is
identical in male and females

What if this gene inadvertently goes onto an X
chromosome?
◦ XX male – estimated 1 in 20,000

What if this gene is missing from a male?
◦ XY female- estimated 1 in 20,000

"Nature's impulse is to create a female“
◦ in the absence of HY antigen (early) or male sex
hormones (later in prenatal development), the
organism will develop as female
◦ male hormones (androgens like testosterone and
dihydrotesterone) are necessary for undeveloped
tissue to develop into male internal and external
sex organs

AIS – androgen insensitivity syndrome
◦ a genetic abnormality whereby there are
androgen receptors but they do not respond to
androgens
 females – little body hair
 males – internal gonads – testes;
 what after that?
 1 in 65,000 males estimated
 often diagnosed at puberty




estimates 1 in 13,000 to 1 in 16,000
overactive adrenal gland releases excess
androgens
diagnosed in females at birth – because of
ambiguous genitalia
males not usually diagnosed at birth


5 alpha reductase is the enzyme that
produces the androgen DHT
(dihydrotestosterone)
DHT is important (apparently) for the
production of male external genitals

guave doces; Dominican Republic
◦ first reported in 1974


early cases – first raised as girls………
What does it say about biology vs vs
environment for determining human sex
roles?

intersex condition in which indvl born with
ovarian and testicular tissue
can be one on one side; the other on the
other or more often one or both gonads is an
“ovotestis” containing both
very rare

can see XXY, XX/XY, XX XXY




CNS – clearly affected by both organizational
and activational effects of steroid hormones
Rodents have been used to gain a
tremendous amount of info about the role of
organizational and activational effects of
steroid hormones
organizational
activational
behavior
organizational
activational
behavior
castrate male
give T
no sex
no aggression
castrate + T inj no T
no sex
no aggression
castrate + T inj give T injections typical male
behavior
T normal
castrate as
adult
little sex
little aggression

In species that have multiple births;
developing embryos can be affected by
hormones from surrounding fetuses
0M, 1M and 2M
females; exposed
to varying levels of
male hormones
from developing
sib nearby






aggression
male sexual
behavior
rough-and-tumble
play
sexual attractiveness
onset of puberty
AG distance

differences in all of
these behaviors
depending on
whether it is a 0M or
2M female


so data from numerous species that bear
multiple offspring at the same time, prenatal
hormones can have an influence on later
structures and behavior!
What about human conditions?
What are some alternative explanations?

What role does activational effects of T play
on male sexual behavior?

So organizational effects of steroid hormones
are critical for setting up circuitry for
behaviors that are “sexually dimorphic” and
activational effects are critical for activating
the circuits in lower animals –

What role do activational effects of T play on
male sexual behavior?
◦ in rats and lower species – obvious
◦ in humans – somewhat less obvious but definitely
still important

McQuay
◦ a former school bus driver in prison in TX for
sexually attacking a young boy (1989)
◦ 1995 – as he approached parole asked state of TX
to be castrated; claimed he would repeat the crimes
if not castrated
 attempted it himself in cell with a razor
 lots of people volunteered the money for the cost of
surgery
In a letter to the editor published in The Dallas Morning
News on Sunday, McQuay said he expects to be released
soon because of his clean disciplinary record.
"... I will be required to look for work and so forth, meaning I
will be walking the streets of your city, your community, your
neighborhoods," McQuay wrote.
"And without a doubt, there will be children around. You tell
me what is likely to happen if I am not castrated before I am
released.“

1996 – California became the first state to
pass chemical castration law

1996 – California became the first state to
pass chemical castration law
◦ requires chemical castration of any person found
guilty a 2nd time of specified sex offenses
◦ Florida, Georgia, Louisiana, Montana, Oregon,
Texas and Wisconsin followed shortly thereafter
with similar laws

Depo-Provera –
◦ lowers testosterone and resulting sex drive in men
◦ originally (and still used) as female contraceptive
◦ most states say that repeat offenders may be
offered it as a condition for their parole

Danish study
◦ 5 out of 117 castrated sex offenders relapsed
over an 18 year period, 1/10th of the rate of non
castrated offenders


Depro-Provera cut recidivism rates of
pedophiles in California, Texas, and some
European countries using it.
Some studies suggest that recidivism falls
to 5%; sexual fantasies are lessened

some may not be able to tolerate med
◦ headaches, nausea, high blood pressure, possible
diabetes, gallstones, hypertension, increased risk of
stroke, loss of bone density

some that have been on it for years must go
off