Behavioral Genetics Friday Lecture Series Part 2

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Behavioral Genetics Friday Lecture SeriesPart 2

• Presented by
• Allie Bailey
• allie_at_ualberta.ca

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Digit Ratio (2D4D) an indicator of prenatal
testosterone a predictor of certain personality
and behavioral traits
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Last time we discussed

• What is digit ratio (2D4D)?
• 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 (2D4D)?
2D
Finger Tip
4D
Basal Crease
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Males and Females Differ

• Digit Ratio is a sexually dimorphic trait

Female
Male
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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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The BIG Idea (Austin et al., 2002)
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The BIG Idea (Austin et al., 2002)
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2D4D and Homosexuality

• Is homosexuality influenced developmentally by
  prenatal testosterone?
• Most widely studied trait in relation to digit
  ratio across different labs
• Findings are not all consistent, but typically
  see a trend in the data

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Homosexual men have on average lower left 2D4D
than controls (plt0.001)
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Sexual orientation measured numerically
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Exclusively homosexual men had higher 2D4D than
bisexual men
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Heterosexual men had higher digit ratios than
homosexuals
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Conclude

• Gay men are hypermasculinized (ie. lower digit
  ratios higher levels of prenatal testosterone)

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Contrast to Robinson Manning (2000)
Williams et al., 2000
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Conclude

• Gay women have masculine digit ratios
• Gay men have hypermasculine digit ratios
  (maybe, but depends on number of older brothers)

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Rahman Wilson, 2003

• Gay men have significantly lower digit ratios
  than heterosexual males
• Gay women also have significantly lower digit
  ratios than heterosexual females
• Both of the above in right digit ratio ONLY
• Conclude homosexual hypermasculinized in both
  sexes

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Brown et al., 2002
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Conclude

• Fetal testosterone plays a role in only some
  cases of female homosexuality
• dependant on category

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Hall Love, 2003

• MZ female twins discordant and concordant for
  sexual orientation
• Discordant twins lesbian had lower digit ratio
  than heterosexual twin
• Concordant twins no differences in digit ratio
• Conclude Lesbians have more masculine finger
  length ratios (not significant in males)

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Lippa, 2003
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Lippa, 2003
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Conclude

• Gay men have more feminine digit ratios
• gay women? Inconclusive.

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2D4D and erotic role preferences (McIntyre, 2003)
Conclude Feminine attitudes/preferences are
associated with low digit ratios (i.e.. high
prenatal testosterone)
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Bem Sex Role Inventory and 2D4D
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Digit ratio and sports (Manning et al., 2001)
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Digit ratio and sports
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Digit ratio and sports
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Digit ratio and skiing(Manning, 2002)
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Digit Ratio and Skiing
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Digit Ratio and Skiing
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Digit ratio and spatial ability
But seen Coolican Peters, 2003 and Austin et
al., 2002
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Digit ratio and physical aggression
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Digit ratio and male dominance
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Digit ratio and mental health

• Digit ratio has also been shown to correlate with
  mental abnormalities
• Autism
• Schizophrenia
• Depression
• Emotionality in preschoolers

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Digit ratio and Autism
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Digit ratio and depression
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Any Questions?