Detailed Question Description:For this question, select MUCH longer or shorter only if the difference in length is more than about three quarters of the length of your nail length on the 4th finger. E.g. if your shorter finger's tip only comes up to the bed of the nail on the longer finger, then it is MUCH longer.
A shorter index finder (the bigger the difference between the 2 lengths), the more prenatal exposure to androgens.
Possible & Known Correlations:It has been suggested by some scientists that the ratio of two digits in particular, the 2nd (index finger) and 4th (ring finger) is affected by exposure to androgens such as testosterone while in the uterus and that this 2D:4D ratio can be used as a crude measure for prenatal androgen exposure.
The digit ratio is the ratio of the lengths of different digits, fingers or toes, typically as measured from the bottom crease where the finger joins the hand to the tip of the finger.
The 2D:4D ratio is sexually dimorphic: in men, the second digit tends to be shorter than the fourth, and in females the second tends to be the same size or slightly longer than the fourth. Some would prefer to say that this trait is 'sexually differentiated' rather than 'sexually dimorphic' in recognition of the fact that the effect size is fairly small (2D:4D distributions of the two sexes overlap to a great degree), especially as compared to other sexually dimorphic traits such as height.
Correlation between digit ratio and traits
Some authors suggest that digit ratio correlated to health, behavior, and even sexuality, in later life. What follows is a non-exhaustive list of some traits which have been either demonstrated or suggested to correlate with digit ratio.
Physiology and disease
Sperm counts (Manning et al 1998)
Heart disease (Manning & Bundred 2001)
Obesity & Metabolic syndrome (Fink, Manning, Neave 2005)
Psychological disorders
Autism (Manning et al 2001)
Depression (Bailey & Hurd, 2005b)
Schizophrenia (Arato et al 2004)
Physical and competitive ability
Skiing (Manning 2002b)
Soccer ability (Manning & Taylor 2001)
Sporting ability in females (Paul et al 2006)
Financial trading (Coates et al 2009)[1]
Cognition and personality
Assertiveness in women (Wilson 1983)
Spatial ability (van Anders & Hampson 2005)
Aggression (Benderlioglu & Nelson, 2004 , Bailey & Hurd 2005a)
Masculinity of Handwriting (Beech and Macintosh 2004)
Perceived 'dominance' and masculinity of man's face (Neave et al 2003; Burriss et al. 2006)
Personality (Austin et al 2002, Fink et al 2004, Luxen & Buunk 2005)
Exam scores: a higher ratio is correlated with higher exam scores among male university students (Romano et al 2006)
Musical ability (Sluming et al 2000)
Sexual orientation
Bem sex role score in women (Csatho et al 2003), erotic role preference in men (McIntyre 2003)
Lesbians vs. straight women, butch vs. femme lesbians (Brown et al 2002)
http://msu.edu/~breedsm/pdf/ButchFemme.pdf
Gay vs straight men and the very odd Europe vs. North American straight man effect (reviewed in McFadden et al 2005 [2]).
Difference in digit ratio between identical female twins discordant for sexual orientation (Hall & Love 2003)
Fraternal birth order effect on digit ratio (Williams et al 2000).
http://msu.edu/~breedsm/pdf/breedlove2000.pdf
Transsexualism
A recent study in Germany has found a correlation between digit ratio and male to female transsexualism. Male to female transsexuals were found to have a higher digit ratio than control males, but one that was comparable to control females. (Transmen showed ratio comparable to biological females.) (Schneider, Pickel & Stalla 2005)
Digit ratio and handedness, autism, other immune diseases
There is some evidence that testosterone facilitates the differentiation of the brain both prenatally and postnatally. There have been many extensions of this, such as the Geschwind-Galaburda Hypothesis, that immune diseases (Geschwind and Galaburda, 1985) and autism (Baron-Cohen et al., 2004) are related to prenatal testosterone, this also explaining why more men are left-handed, autistic, etc. than women. Prenatal exposure to testosterone is thought to promote the development of the right-hemisphere and increase the incidence of sinistrality. As such low 2D:4D was found to be associated with improved left-hand performance (Manning et al 2000, Fink et al 2004).
Digit ratio and development
There is some evidence that 2D:4D ratio may also be indicative for human development and growth. Ronalds et al (2002) showed that men who had an above average placental weight and a shorter neonatal crown-heel length had higher 2D:4D ratios in adult life. Moreover, studies about 2D:4D correlations with face shape suggest that testosterone exposure early in life may set some constraints for subsequent development. Prenatal sex steroid ratios (in terms of 2D:4D) and actual chromosomal sex dimorphism were found to operate differently on human faces, but affect male and female face shape by similar patterns (Fink et al 2005). However, exposure to very high levels of testosterone and/or estrogen in the womb may have also negative effects. Fink et al (2004) found that men with low (indicating high testosterone) and women with high (indicating high estrogen) 2D:4D ratios express lower levels of facial symmetry .
Cancer
Oimitrios Tricopou1os, an epidemiologist at Harvard University, proposed a decade ago that breast cancer may originate in utero (The Lancet, vol. 335, p 939). He suggested that high concentrations of estrogen may create a "fertile soil" for cancer to develop later in life, He also thought that variability in estrogen levels during pregnancy may help to explain why breast cancer rates are generally higher in women born to Caucasian mothers compared with those born to Oriental or younger mothers. Recently he and his colleague Karin Michels showed that high birth weight in girls-another sign of high prenatal estrogen levels-was associated with an increased risk of breast cancer.
Handedness
Children with low 2D:4D ratios suggestive of high exposure to testosterone in the womb-are more likely to be quicker with their left hands than the kids with higher ratios. This, he says, suggests that our degree of left-handedness and more generally the way the brain divides up tasks between left and right hemispheres - may be influenced by hormone levels in the womb.
Autism
Children with low 2D:4D ratios suggestive of high exposure to testosterone in the womb-are more likely to be quicker with their left hands than the kids with higher ratios. This, he says, suggests that our degree of left-handedness and more generally the way the brain divides up tasks between left and right hemispheres - may be influenced by hormone levels in the womb.
Manning has begun examining autism too. He teamed up with Simon Baron- Cohen and Svetlana Lutchmaya from the University of Cambridge, who have used samples of amniotic fluid to directly measure the levels of hormones that babies are exposed to in the womb. When the children reached their first birthday, the researchers measured their vocabularies and ability to make eye contact. Poor language skills and an unwillingness to make eye contact are early hallmarks of autism. They found that babies who'd been exposed to high levels of testosterone in the womb fared the worst.
"What we're hoping to look at is whether finger ratios can be used as a proxy for hormones," says Lutchmaya. Amniocentesis is a risky procedure that only a few mothers choose to undergo, she says. But by measuring finger lengths instead, researchers can assess a random sample of children for possible early signs of impaired language and social skill development. Currently, they are checking the fingers of children for whom they have amniotic samples. Meanwhile, Manning and Baron-Cohen have looked at the finger ratios of 49 children with firm diagnoses of autism, 23 with a mild form of the disorder called Asperger's syndrome, and their families. The researchers found that autistic children tended to have very low 2D:4 ratios. Interestingly, children with Asperger's syndrome had ratios that fell between those of autistics and unaffected children. "It fits exceptionally well with the theory," says Manning.
Musical Ability
Manning recruited 54 male musicians from a British symphony orchestra. He discovered that these men had significantly lower 2D:4D ratios than controls-they had a very "masculine" ratio. Even more striking, when he compared the top-ranked "first" musicians with their lower-ranked colleagues--a measure of their relative ability-the former had significantly lower 2D:4D ratios. Could testosterone really predispose the brain to be more tuned in to music? Manning thinks so.
Aggression
The research, done at the University of Alberta and announced Wednesday, found a connection between the length of the male index finger relative to the ring finger and the tendency to be aggressive. No such connection was found in women.
Examination marks of male university students positively correlate with finger length ratios (2D:4D)
Maria Romano, Barbara Leoni and Nicola Saino; Università degli Studi di Milano; 13 October 2004 -
Intersexual and intrasexual variation in second to fourth digit length (2D:4D) in humans may result from differential exposure to fetal testosterone. 2D:4D predicts several physiological, psychological and performance traits in adulthood. These relationships may reflect the ‘pleiotropic’ effects of testosterone on development of digits and diverse organ systems, which are expressed in adulthood. We hypothesized that 2D:4D also predicts academic success of students. 2D:4D of right hand positively predicted examination marks of males from two three-year degree courses (TYDCs). Marks of females did not covary with 2D:4D. Males from the two TYDCs differed in 2D:4D. The present results thus add to the rapidly accumulating literature on 2D:4D showing correlations with phenotypic traits in humans. If testosterone affects 2D:4D and intellectual performance, our results suggest that testosterone levels are under stabilizing selection because of effects on performance traits documented in previous studies and antagonistic effects on intellectual performance (present study).
More Info:
http://www.human-nature.com/nibbs/02/manning.html
http://www.palmistry.org/fing.html
Length of index and ring fingers differentially influence sexual attractiveness of men's and women's hands - Saino, N., Romano, M., Innocenti, P. 2006
Digit ratio (2D:4D) moderates the impact of an aggressive music video on aggression - Millet, K., Dewitte, S. 2007
Index to ring finger length ratio and the risk of osteoarthritis - Zhang, W., Robertson, J., Doherty, S., Liu, J.J., Maciewicz, R.A., Muir, K.R., Doherty, M. 2008
2d:4d, sex steroid hormones and human psychological sex differences - Vermeersch, H., T'Sjoen, G., Kaufman, J.M., Vincke, J.
Question Help: 
