Hormones, morphometrics and behaviour - practical 3

Question 1

2D:4D ratio

Answer 1

(Hönekopp et al., 2007)

Affected by exposure to androgens, e.g. testosterone

Provides a crude measure for prenatal androgen exposure, w/ lower 2D:4D ratios linked to higher androgen exposure

No correlation between 2D:4D and sex hormone levels as adult – strictly exposure in utero that causes diffs

Question 2

what’s the mechanism behind 2D:4D ratio?

Answer 2

Unclear

Other traits, e.g. arm-to-trunk length ratio, show similar effects

Possible influence of genes via pleiotropy: development of both digits and genitals governed by Hox genes

Sex hormones may affect bone growth directly/via regulation local Hox genes

Question 3

sex differences in the 2D:4D ratio

Answer 3

Males: mean 0.947 +- 0.029

Females: mean 0.965 +- 0.026

Question 4

ethnic differences in the 2D:4D ratio

Answer 4

Ratios vary greatly between diff ethnic groups – more than between sexes

‘More diff between a Pole and a Finn than man and a woman’ (Manning et al., 2004)

Question 5

predicting adult traits

Answer 5

(Manning, 2008)

High ratio associated with:

• Lowered sperm counts
• Increased risk for heart disease in males
• Increased rate of psychopathy in females
• Increased risk for anorexia nervosa in females
• Lower assertiveness in females
• Reduced aggression in males
• High exam scores among male students
• Lower musical ability in males

Question 6

does 2D:4D ratio predict level of risk taking?

Answer 6

No significant effect of digit ratio

Significant effect of sex on risk taking – men are riskier –based on sample of 4 men – not reliable

Question 7

does the ratio predict reaction time?

Answer 7

No significant effects of any variables

Question 8

why do our results differ from the Coates et al. (2009) study?

Answer 8

Different samples

Confounding variables in tasks

Different types of risks – more sustained for Coates

Question 9

fWHR

Answer 9

(Weston et al., 2007)

fWHR = (bizygomatic width) / (upper facial height)

higher in adult males than females – men have relatively wider upper faces than women

due to divergence of bizygomatic width in puberty, coinciding with testosterone surge in boys

Question 10

Carré and McCormick (2008)

Answer 10

ice-hockey players with wider faces commit more aggressive acts

Question 11

Stirrat et al. (2012)

Answer 11

Forensic evidence: men with narrower faces stat more likely to die from contact violence

Question 12

Little et al. (2015)

Answer 12

Based solely on photos (N = 114 pairs), fight winner was:

• More often predicted to be winner
• Rated as more aggressive
• Rated as stronger
• Rated as more masculine
• Rate by women as more attractive

Sensitivity to cues of fighting ability may be evolutionarily imp

But not known what cues used – could fWHR play a role?

Question 13

could the fight winner be reliably predicted?

Answer 13

no

Question 14

does fWHR differ between winners and losers?

Answer 14

no

Question 15

did you judge fighters with wider faces as more attractive?

Answer 15

no

Question 16

Did your results differ from those of Little et al. (2015)? Why?

Answer 16

Bigger sample – 114

Other cues used

Question 17

Why might we be sensitive to cues of fighting ability?

Answer 17

Evolution – don’t fight someone that will beat you

Know when not be aggressive

Know who will protect them better for females

For men: knowing who (not) to pick fights with

For women: identifying who can best defend her and provide for her offspring