behavioral genetics friday lecture series
DESCRIPTION
TRANSCRIPT
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Why are some individuals more aggressive than others?
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Activational vs. Organizational Testosterone
Activational: short-term effects of hormones which trigger behavior
Organizational: long-term effects of exposure to hormones during development
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Activational Effects of Hormones
Testosterone Aggressive Behavior
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The Reciprocal Model
A cyclical relationship exists between aggressive behavior and activational testosterone
Aggressive Behavior Testosterone
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The Reciprocal Model
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The Reciprocal Model
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The Reciprocal Model
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Organizational Effects of Testosterone on Aggression
• Animal Models– Mice (vom Saal & Bronson, 1980)– Lizards (polymorphic throat badges)
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Organizational Effects of Testosterone on Aggression
• Humans– high risk spontaneous
abortions (treated with progestins & estrogens)
– Congenital Adrenal Hyperplasia (CAH)
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Digit Ratio: an indicator of natural variations in prenatal
testosterone Fact or Fiction?
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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
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What is digit ratio (2D:4D)?
Basal Crease
Finger Tip2D4D
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Males and Females Differ
•Digit Ratio is a sexually dimorphic trait
Female Male
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History of digit patterns
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First year U of A students’ 2D:4D
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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)
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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
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Ethnicity plays a role in 2D:4D
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2D:4D and Other Species
How do you measure 2D:4D in mice?
Brown et al. (2003) method
Bailey et al. (in press) method
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2D:4D is sexually dimorphic in laboratory mice
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But not in inbred strains...
Digit ratio differs between strains, but not between sexes within a strain (Bailey & Hurd, in press)
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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).
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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).
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CAH and 2D:4D (Brown et al., 2002)
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CAH and 2D:4D (Buck et al., 2003)
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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
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Hox genes and 2D:4D
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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
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2D:4D and the Androgen Receptor Gene
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Fetal testosterone/estradiol and 2D:4D (Lutchmaya et al., 2004)
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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
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Hypothesis
Testosterone organizes human aggressive behavior and therefore, 2D:4D will correlate with adult
aggressive behavior.
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Methods
•298 Introductory Psychology Students
•Questionnaire•Aggression Questionnaire (Buss & Perry, 1992)
•Hostility (Cognitive)•Anger (Emotional)•Verbal (Instrumental)•Physical (Instrumental)
•Paulhus Deception Scale (PDS)
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Methods
Digital Imaging of Hands
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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
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ResultsPhysical aggression is the most sexually dimorphic aggression subscale therefore, of the 4 subscales it should most strongly correlate with digit ratio.
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Results
Physical aggression was the only subscale to correlate with digit ratio
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Results
Males with lower 2D:4D had higher physical aggression scores
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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)
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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
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Future Research
2D:4D and physical aggression in hockey players
Do aggressive penalty minutes correlate with digit ratio?
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Any Questions?