Sex differences
Messinger
Gender film clips
Bonobo
Overview
Biology's role
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“Experiments with nonhuman primates
show that administering testosterone to
female fetuses late in gestation yields
more typically masculine behavior.”
Placement of rat fetuses in utero
influences sex-typed behavior
Many sex differences are continuous, not
categorical

E.g. estrogen and testosterone
Sex Differences in Early
Infancy

“girls show stronger visual
preferences for a doll (i.e., an object
with human attributes) than for a
toy truck
• (Alexander, Wilcox, & Woods, 2009)…

boys shortly after birth show
stronger visual preferences for a
mechanical mobile than for a face
• (Connellan et al., 2000)”
Alexander, G. M., & Wilcox, T. (2012). Sex Differences in Early
Infancy. Child Development Perspectives, 6(4), 400-406. doi:
10.1111/j.1750-8606.2012.00247.x
Feedback

Between physical and social features
z
Simpson, Nicolini, Shetler, Suomi, Ferrari,&
Paukner (2016)
Experience-independent sex
differences in newborn macaques:
Females are more social than
males
z
Background
 Gender differences may be attributed to different evolutionary
pressures

Females – primary caretakers

increased social interests & skills interpreting expressions 
increased offspring survival
 However, male and female human infants are treated differently
from birth
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Parents handle male infants more “rough” & spend more time in
synchronous interactions with mothers
Offer female infants more verbal stimulation & get more parentchild interaction overall
z
Current Study
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Nonhuman Primate Studies
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More control over experiences and environments
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Macaques have similar patterns in sex-related differences
Goal: assess sex differences in macaque infants raised in
homogenous controlled environments (nursery)
z
_
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Methods
48 healthy, full term macaques
(21 Female)
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Separated from mothers at
birth
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Tested before exposed to
social groups
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Eye tracking test at 2-3 weeks
old
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Human interaction task at 4-5
weeks old
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_
Eye Tracking Task
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Across both measures there are main
effects of sex
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Females look at faces longer regardless of
expression than their male counterparts
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Females also specifically spend more time
looking to the eyes and mouths of the face
z
_
Human Interaction Task
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Sex differences only in Affiliative
Social Behaviors
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Females significantly outperformed
the males
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Take-homes
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First study to provide evidence for “experience-independent” sex differences
in social behaviors soon after birth in any primate (humans included)
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Limitations:
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No control stimuli
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Possible subtle differences in the way caregivers treated infants
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Disentangle social skills & social motivation
Questions?
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How do you feel about the procedures in both eye tracking task and human
interaction task?
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Do you expect similar results if we could do this with human infants?
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Pre-natal environment differences?
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Did you buy it?
Male newborns
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‘Less responsive to social stimuli
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less able to maintain eye contact
Greater difficulties in maintaining
affective regulation
Smile less and display more irritability,
crying, facial grimacing, and lability of
emotional states
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
more rapid buildup of arousal
engage in less self-comforting’
• Weinberg et al., p. 175
Face-to-face
Joy
Interest
Anger
Look @ Mom
Look @ Object
Neutral/Positive
Vocalizations
Fussy Vocalizations
Boys
.26
.55
.07
.42
.35
.13
Girls
.16
.68
.03
.35
.45
.06
.09
.04
(Weinberg et al.)
Mothers more likely to
talk to
 engage in face-to-face interaction
 hold and touch
 their male infants
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possibly in an attempt to soothe them
Differential social
expectations
Pervasive: TV, media
 Experimentally demonstrated
 Define normative expectations of
everyday behavior and
 Define boundaries of acceptable
behavior
 At the most intimate and the most
mundane levels
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Maccoby
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"By and large, the daily routines of
family life do not have much impact
on the strong tendency of children
to separate into same-sex groups,
and probably not on the distinctive
activities enacted by male and
female groups," Maccoby said.
Gender segregation
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Research on gender typing in
individuals is inconclusive
Clustering of gender-typed
characteristics weak
 Relations to family characteristics weak
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Same-sex groupings predominate
From 3 – 12,
 Cross-cultural phenomenon
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Constructivist argument
Innate gender-specific proclivities
 Lead to same sex segregation
 Which creates gender-specific
socialization
 Children create themselves playing
with each other
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IS THIS POSSIBLE?
Same-sex groupings

Boys
 Larger groups
 More
conflict/competition
 Cohesiveness
 More autonomous
from adults
Differential
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Girls
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Smaller, more
dyadic
Less conflict, more
responsive
Less goal-oriented,
more intimate
exposure to these groups
influences individual behavior
Sex differences
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With increasing age, boys and girls
in preschool interact with members
of the same sex
•
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(e.g., Fabes, Shepard, Guthrie, & Martin, 1997; Maccoby & Jacklin, 1987; Martin & Fabes, 2001).
By 4-5 years of age, both boys and
girls are observed interacting with
same sex peers at three to four
times the frequency that they
interact with other sex peers.
Day-to-day variability
Girls
Same-sex
preference
Other-sex
preference
Boys
Dynamic system approach
to gender research

Long term changes and short term
interactions.
Lynn Martin, C., Fabes, R. A.,
Hanish, L. D., & Hollenstein, T.
(2005). Social dynamics in the
preschool. Developmental
Review, 25(3–4), 299-327. doi:
http://dx.doi.org/10.1016/j.dr.20
05.10.001
“Fig. 4A represents the state space
pattern that might be seen for a socially
competent boy who is solely attracted to
other socially competent children. “
“Fig. 4B illustrates a pattern based on sex
similarity. In this case, the events
represented on this boy’s state space
illustrate that he is seen interacting only
with boys and it does not matter what
type of social behavior they tend to
display. “
“Fig. 4C depicts the landscape for a
socially competent boy whose state space
is shaped by both similarity on social
behavior and on sex. The events cluster in
the region of socially competent boys. If
this pattern occurred, it would suggest
that behavioral similarity matters but only
in consideration for same-sex peers.”
Sex-Segregated
Interactions
New approaches
Child Mobility.ppt
Digit Ratio (2D:4D) and
attachment styles in middle
childhood: Indirect evidence
for an organizational effect of
sex hormones
Marco Del Giudice & Romina
Angeleri (2015)
Will
M.
Life history theory
How to make trade-offs between
growth, maintenance, and
reproduction over the life course
given a limited amount of energy.
“Fast” strategy: mature early, reproduce early,
have many offspring, invest less in them, die
earlier
E.g., Salmon
“Slow” strategy: mature late, reproduce later, have
fewer offspring, invest more in them, die later
E.g., Humans
Will M.
Does 2D:4D digit ratio predict
attachment in middle childhood?
Second digit typically shorter, but
difference between lengths of the two
digits greater in males than females.
 Rough-and-ready measure of early
exposure to androgen and estrogen.
 Should predict differences in insecure
attachment in both sexes
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Will M.
Mean digit ratio higher in
females
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Females score lower in avoidance, higher
in ambivalence
No sex differences in secure attachment
More feminine ratios associated with less
avoidance, more ambivalence, not felt
security
Will
M.
Aggression type and gender
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Boys more physically victimized by their
friends.
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Friend physical victimization was particularly
related to boys adjustment difficulties
Girls more relationally victimized.
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Friend relational victimization was particularly
related to girls’ adjustment difficulties.
Crick & Nelson, 2002.
Prediction
Cross-sex friendships
Pre-school
 Elementary school
 Middle school
 High school / Adolescence …
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Change
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12th grade
Boys 5 hrs a week w girls.
 Girls 10 hrs a week w boys.
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Larger network of other-sex friends
increases odds of romantic
relationship
Extreme male brain
theory of autism
Baron-Cohen
Empathizing
(theory of mind)
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“Empathizing is the
capacity to predict
and to respond to the
behavior of agents
(usually people) by
inferring their mental
states and
responding to these
with an appropriate
emotion.”
Systemizing
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“Systemizing is the
capacity to predict and
to respond to the
behavior of
nonagentive
deterministic systems
by analyzing inputoperation-output
relations and inferring
the rules that govern
such systems.”
Females and males
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“At population level, females are stronger
empathizers and males stronger systemizers.
“Eextreme male brain’’ theory: autism
represents an extreme of the male pattern
(impaired empathizing and enhanced
systemizing).
Specific aspects of autistic neuroanatomy may
also be extremes of typical male
neuroanatomy.”
You can be high in both… or
low in both
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Higher on graph
– more
empathizing
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Lower – less
empathizing
More to right –
higher
systemizing
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More left – less
systemizing
AS/HFA>Male>Female
AS/HFA>Male>Female
Sex differences attenuated
in ASD….
Baron-Cohen, S.,
Cassidy, S., Auyeung, B.,
Allison, C., Achoukhi, M.,
Robertson, S., Pohl, A.,
& Lai, M.-C. (2014).
Attenuation of Typical
Sex Differences in 800
Adults with Autism vs.
3,900 Controls. PLoS
ONE, 9(7), e102251. doi:
10.1371/journal.pone.01
02251
What about the development
of ASD?
Messinger, D. S., Young, G. S., Webb, S. J., Ozonoff, S.,
Bryson, S. E., Carter, A., Carver, L., Charman, T.,
Chawarska, K., Curtin, S., Dobkins, K., Hertz-Picciotto, I.,
Hutman, T., Iverson, J. M., Landa, R., Nelson, C. A.,
Stone, W. L., Tager-Flusberg, H., & Zwaigenbaum, L.
(2015). Early sex differences are not autism-specific: A
Baby Siblings Research Consortium (BSRC) study. Mol
Autism, 6, 32. doi: 10.1186/s13229-015-0027-y
Proportion ASD
Relative risk of ASD = 3.18
Sex by domain
not affected by group
Repetitive Behaviors
Social Affect
Sex by subtest
not affected by group
Conclusion
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Sex differences in ASD prevalence
No sex differences in overall symptoms or
cognition
• Boys (higher RRB) and girls (higher language)
with ASD differ in specific performance areas
• These sex differences exist in ASD, non-ASD,
low-risk
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Results are consistent with recent reports
Sex differences that appear in children
with ASD may not be ASD-specific
Effect of
female
sibling
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Palmer, N., Beam, A., Agniel, D., Eran, A.,
Manrai, A., Spettell, C., . . . Kohane, I.
(2017). Association of Sex With Recurrence
of Autism Spectrum Disorder Among
Siblings. JAMA Pediatr. doi:
10.1001/jamapediatrics.2017.2832
Homosexuality as a
Discrete Class
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Previous research on the latent structure of sexual orientation has
returned conflicting results, with some studies finding a dimensional
structure (i.e., ranging quantitatively along a spectrum) and others a
taxonic structure (i.e., categories of individuals with distinct
orientations).
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Low-base-rate same-sex-oriented taxa for men (base rate = 3.0%) and
women (base rate = 2.7%).
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The current study used a sample (N = 33,525) from the National Epidemiologic Survey on
Alcohol and Related Conditions (NESARC). A series of taxometric analyses were conducted
using three indicators of sexual orientation: identity, behavior, and attraction.
Generally, taxon membership conferred an increased risk for psychiatric and substance-use
disorders.
Although taxa were present for men and women, women demonstrated
greater sexual fluidity, such that any level of same-sex sexuality
conferred taxon membership for men but not for women.
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Norris, A. L., Marcus, D. K., & Green, B. A. (2015). Psychological Science. doi:
10.1177/0956797615598617
Female Bisexuality From Adolescence to Adulthood:
Results From a 10-Year Longitudinal Study. Lisa Diamond
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3 conceptualizations of bisexuality
1. “Transitional phase”
2. Third type of sexual orientation
3. Heightened capacity for fluidity
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Present study
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79 non-heterosexual women
10 years, 5 assessment points. At each:
• Label self sexual identity
• Lesbian, bisexual, “unlabeled”
• % daily attractions that are same-sex
• #of sexual contacts with men & women
(since last assessment)
Nayfeld
Identity
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Changing identity
• 73% of T1 bisexuals
• 83% of T1 “unlabeled”
• 48% of T1 lesbians

Bisexual and
unlabeled women
more likely to change
identity labels, χ2(2,
N = 79) = 8.3, p < .02.
More likely to switch between bisexual
and unlabeled IDs than to settle on
lesbian or heterosexual labels.
• 2/3 of ID changes: adopting bisexual or
unlabeled identity.

% identifying as bisexual or “unlabeled”
• T1 T2
T3
57% 47% 51%
T4
T5
57% 58%
Nayfeld
Sexual
Attractions
•Same-sex attractions
declined significantly
among lesbians only
•Women who gave up
bisexual/lesbian IDs
still reported bisexual
patterns of attraction in
T5
Nayfeld
Sexual Behavior
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Consistent decline in same sex behavior
among all women
NOT matched by a parallel decline in
same-sex attractions
By 2005, most women involved in long
term monogamous relationships.
70% of T5 lesbians, 89% of bisexuals, 85% of
unlabeled women, 67% of heterosexuals

By 2005, 60% of T1 lesbians had had
sexual contact with a man, and 30% had
been romantically involved with a man
Resolved by change in identity to
bisexual/unidentified
Nayfeld
Discussion
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•
•
Bisexuality as stable pattern of attraction
to both sexes, with balance varying based
on personal and situational factors.
Identity change more common than
identity stability
ID change reflects shifting experiences
Adopt labels consistent with relationship status
Seek to maximize fit with own prevailing pattern
of attraction/behavior
Nayfeld