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Assignment two
Much research has been conducted looking into the area of the human anatomy of the lengths of digits on the hand, particularly research into the 2D:4D digit ratio. The 2D:4D is a sexually dimorphic trait found in humans Hömekopp and Watson (2010 from a meat-analysis) and refers to the lengths of the 2nd digit/ finger (pointer) and the 4th digit/ finger (ring) and it is believed that this length is predisposed from exposure to different hormones in the utero Manning (2002). It has been hypothesized that the 2D:4D is a biomarker that is caused from parental testosterone and parental estrogenic Manning (2002) and is believed that a child’s 2D:4D is fully formed within the first 13 to 14 weeks of pregnancy (Phelps. 1952). Knickmeryer and Manning (2004) found a negative association of the ratio between testosterone and estradiol in the amniotic fluid, on the other hand high testosterone to estradiol levels have been associated with smaller 2D:4D digit ratios. On the other hand higher 2D:4D digit ratio has been associated with higher levels of estradiol to testosterone Manning et al (1998). It has also been found that males have a slightly smaller digit ratio to women Baile (2004).
The 2D:4D digit ratio has been liked with a plethora of human behaviours such as aggression (Manning, 2013) and gender identity (Kangassalo, 2011). However there has been much research into the length of the 2D:4D digit ratio and individual differences to self-perceived attractiveness, self-esteem and body- esteem; particularly in women (wade, 2003). One of the most influential psychologist exploring this area was Wade who hypothesised that women with a high 2D:4D digit ratio would find themselves more attractive. To test this hypotheses Wa...

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... T., Stewart, A., Bundred, P. E., & Trivers, R. L. (2004). Sex and ethnic differences in 2nd to 4th digit ratio of children. Early Human Development, 80 (2), 161 – 168

Manning, J.T., Scutt, D., Wilson, J., and Lewis-Jones, D.I. (1998). The ratio of 2nd to 4th digit length: A predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen. Human Reproduction,13 , 3000–3004
Manning, J. (2013). Digit Ratio (2D:4D), Aggression, and Testosterone in M en Exposed to an Aggressive Video Stimulus. Evolutionary Psychology. 11 (5), pp 953 - 964.

Kangassalo, k. (2011). Prenatal Influences on Sexual Orientation: Digit Ratio (2D:4D) and Number of Older Siblings. Evolutionary Psychology. 9 (4), pp 496-508.

Baile, A. (2004). Finger length ratio (2D:4D) correlates with physical aggression in men but not in women. Biological Psychology. 5 (1), 2-3.

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