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Why are some individuals more aggressive than others?
Activational vs. Organizational Testosterone
Activational: short-term effects of hormones which trigger behavior
Organizational: long-term effects of exposure to hormones during development
Activational Effects of Hormones
Testosterone Aggressive Behavior
The Reciprocal Model
A cyclical relationship exists between aggressive behavior and activational testosterone
Aggressive Behavior Testosterone
The Reciprocal Model
The Reciprocal Model
The Reciprocal Model
Organizational Effects of Testosterone on Aggression
• Animal Models– Mice (vom Saal & Bronson, 1980)– Lizards (polymorphic throat badges)
Organizational Effects of Testosterone on Aggression
• Humans– high risk spontaneous
abortions (treated with progestins & estrogens)
– Congenital Adrenal Hyperplasia (CAH)
Digit Ratio: an indicator of natural variations in prenatal
testosterone Fact or Fiction?
Outline
•What is digit ratio (2D:4D)?
•History of digit ratio
•Sexually dimorphic and stable (humans & other species)
•Indirect evidence of digit ratio as an indicator of prenatal testosterone
•CAH studies
•Hox genes
•Androgen receptor gene
•fetal testosterone study
What is digit ratio (2D:4D)?
Basal Crease
Finger Tip2D4D
Males and Females Differ
•Digit Ratio is a sexually dimorphic trait
Female Male
History of digit patterns
First year U of A students’ 2D:4D
Digit ratio is stable
-by 13th week of development hand bone proportions are stable
- digit ratio not affected by age (but see Buck et al., 2003)
Sexual dimorphism in digit ratio
• Larger on the right than the left side (humans, mice, & zebra finches)
• Suggested that androgenization affects the right more than the left
• Stronger effects on the right hand when digit ratio has been correlated with psychological factors
• Not due to bones in hand
• 2D:4D most sexually dimorphic of all ratio combinations
Ethnicity plays a role in 2D:4D
2D:4D and Other Species
How do you measure 2D:4D in mice?
Brown et al. (2003) method
Bailey et al. (in press) method
2D:4D is sexually dimorphic in laboratory mice
But not in inbred strains...
Digit ratio differs between strains, but not between sexes within a strain (Bailey & Hurd, in press)
Digit ratio is sexually dimorphic in zebra finches (Burley & Foster, 2004)
•Female digit ratio was lower than male digit ratio (similar to pattern seen in human toes- McFadden & Schubel, 2002)
•Digit ratio positively correlated with egg order in both males and females (decreasing androgen allocation as egg order increases).
Congenital Adrenal Hyperplasia (CAH)
•Autosomal recessive condition
•Results in abnormally high androgen concentrations
•Diagnosed and treated after birth typically (reflects organizational rather than activational testosterone influence).
CAH and 2D:4D (Brown et al., 2002)
CAH and 2D:4D (Buck et al., 2003)
Hox genes
•are highly conserved across species
•38 genes organized in 4 families (Hoxa- Hoxd)
•Hoxa and Hoxd control the patterning of the appendicular skeleton
Hox genes and 2D:4D
Androgen receptor gene (Manning et al, 2003)
X-linked gene that codes for a receptor protein (3 domains)
terminal domain encodes variable length of glutamine repeats (range: 11-30)
determines sensitivity to testosterone
Increased numbers of CAG repeats increased androgen insensitivity
2D:4D and the Androgen Receptor Gene
Fetal testosterone/estradiol and 2D:4D (Lutchmaya et al., 2004)
The BIG Idea (Austin et al., 2002)
•Males and females consistently differ for a number of cognitive & personality traits
•Some of these traits have been theoretically or empirically linked to sex hormones
•If there is a hormonal basis for the sexual dimorphism seen in such traits then there should be an association between 2D:4D and these traits
Hypothesis
Testosterone organizes human aggressive behavior and therefore, 2D:4D will correlate with adult
aggressive behavior.
Methods
•298 Introductory Psychology Students
•Questionnaire•Aggression Questionnaire (Buss & Perry, 1992)
•Hostility (Cognitive)•Anger (Emotional)•Verbal (Instrumental)•Physical (Instrumental)
•Paulhus Deception Scale (PDS)
Methods
Digital Imaging of Hands
Results
Men had smaller digit ratios than women on both their right (p< 0.001) and left (p< 0.001) hands.
Males Females tMean Right 2D:4D 0.946 0.965 -5.35Mean Left 2D:4D 0.951 0.966 -4.28
ResultsPhysical aggression is the most sexually dimorphic aggression subscale therefore, of the 4 subscales it should most strongly correlate with digit ratio.
Results
Physical aggression was the only subscale to correlate with digit ratio
Results
Males with lower 2D:4D had higher physical aggression scores
Conclusions•Prenatal testosterone (as assayed by 2D:4D) predicts male physical aggression
- physical aggression was the most sexually dimorphic trait
•No relationship found between activational testosterone and aggression questionnaire (Archer et al., 1998)
Conclusions
•Our organizational effect of testosterone on physical aggression (rpartial= -0.21, r= -0.17) was larger than average activational relationship (r= 0.14) reported in meta-analyses (Archer et al., 1998; Book et al., 2001).
-different methodologies across studies-testosterone fluctuates daily & seasonally-small unrepresentative samples
Future Research
2D:4D and physical aggression in hockey players
Do aggressive penalty minutes correlate with digit ratio?
Any Questions?
