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Finger Celebrities in Science

Big names in finger measurement
by Alice Shirrell Kaswell and Stephen Drew, Improbable Research staff

Many researchers now spend their careers, and build their professional reputations, studying finger lengths. This new academic field has produced several celebrities. This article gazes at some of the most brightly blazing academic finger stars.

[Editor’s note: For a quick tour through the ever-widening archives of finger research, see “The Meaning of the Finger.”]

Lingo, Lingo
An important piece of finger length lingo is the phrase “2D:4D.”

This is the ratio of the second finger’s length to that of the fourth finger. It is, the studies tell us, the key to almost everything. There is a related, though subtler, concept called “fluctuating asymmetry,” or “FA.” One researcher defines fluctuating asymmetry in a simple phrase: it “represents non-directional deviations from perfect symmetry in morphological characters.”

***

John Thomas Manning, Finger Patriarch
Professor John Thomas Manning of the University of Liverpool is the star of stars, so far as fingers are concerned. Though by no means elderly, Professor Manning is the Grand Old Man of finger-length ratio. An October 17, 2006 profile in the Washington Post says:

In 1998, British researcher John Thomas Manning suggested that the difference between male and female digit ratios stemmed from prenatal exposure to the hormones testosterone and estrogen. If the digit ratio—which is established by the time a fetus is 9 weeks old and remains constant throughout a person’s life—reflects the level of that exposure, Manning reasoned, then it might serve as a marker for other conditions—including predisposition to many diseases—thought to be affected by prenatal hormone exposure.

In 2002 Professor Manning published a book, Digit Ratio: A Pointer to Fertility, Behavior, and Health (Rutgers University Press). The back cover conveys some of the excitement that lies within:

In this book, Manning presents evidence for how 2D:4D correlates with traits ranging from sperm counts, family size, musical genius, and sporting prowess, to autism, depression, homosexuality, heart attacks, and breast cancer.

Here are some of Professor Manning’s most provocative studies.

Manning: Skiing
“The Ratio of 2nd to 4th Digit Length and Performance in Skiing,” J.T. Manning, Journal of Sports Medicine and Physical Fitness, vol. 42, no. 4, December 2002, pp. 446–50. Professor Manning reports:

This preliminary study aimed to assess the relationship between 2D:4D ratio and skiing speed on the basis of times recorded on a 200 m slalom course by 72 skiers. Each skier made 2 individual timed runs and the fastest time was used for comparisons....

Low 2D:4D was associated with fast skiing times.

Manning: Susceptibility to All Disease?
“The Ratio of 2nd to 4th Digit Length: A New Predictor of Disease Predisposition?”, J.T. Manning and P.E. Bundred, Medical Hypotheses, vol. 54, no. 5, May 2000, pp. 885–7. Professor Manning hypothesizes:

The ratio between the length of the 2nd and 4th digits is: (a) fixed in utero; (b) lower in men than in women; (c) negatively related to testosterone and sperm counts; and (d) positively related to oestrogen concentrations. Prenatal levels of testosterone and oestrogen have been implicated in infertility, autism, dyslexia, migraine, stammering, immune dysfunction, myocardial infarction and breast cancer. We suggest that 2D:4D ratio is predictive of these diseases.

Manning: Autism
“The 2nd to 4th Digit Ratio and Autism,” J.T. Manning, S. Baron-Cohen, S. Wheelwright and G. Sanders, Developmental Medicine and Child Neurology, vol. 43, no. 3, March 2001, pp. 160–4. Professor Manning suggests:

2D:4D ratio may be a possible marker for autism which could implicate prenatal testosterone in its aetiology.

Manning: Psychopathological Kids
“Second to Fourth Finger Ratio and Possible Precursors of Developmental Psychopathology in Preschool Children,” J. H. G. Williams, K. D. Greenhalgh and J. T. Manning, Early Human Development, vol. 72, no. 1, May 2003, pp. 57–65.

Manning: Contracting HIV and AIDS
“The Ratio of 2nd to 4th Digit Length: A Proxy for Testosterone, and Susceptibility to HIV and AIDS?”, J.T. Manning, P. Henzi and P.E. Bundred, Medical Hypotheses, vol. 57, no. 6, December 2001, pp. 761–3.

The incidence of HIV and AIDS is high in sub-Saharan Africa and in male homosexuals.... There is evidence that black South Africans have lower 2D:4D ratios than most other populations and male homosexuals have lower 2D:4D ratios than male heterosexuals. Men with low 2D:4D ratios may also be more sexually active and/or more fertile than men with high ratio. We suggest that men and women with low 2D:4D are susceptible to HIV infection and AIDS and babies with low 2D:4D ratio susceptible to vertical transmission.

Manning: Male Sports and Fighting
“Second to Fourth Digit Ratio and Male Ability in Sport: Implications for Sexual Selection in Humans,” J.T. Manning and R.P. Taylor, Evolution and Human Behavior, vol. 22, no. 1, January 2001, pp. 61–69.

Professional football players had lower 2D:4D ratios than controls. Football players in 1st team squads had lower 2D:4D than reserves or youth team players. Men who had represented their country had lower ratios than those who had not... We suggest that prenatal and adult testosterone promotes the development and maintenance of traits which are useful in sports and athletics disciplines and in male:male fighting.

Manning: Male Dominance
“Second to Fourth Digit Ratio, Testosterone and Perceived Male Dominance,” Neave, S. Laing, B. Fink and J.T. Manning, Proceedings of the Royal Society of London B, vol. 270, 2003, pp. 2167–72.

Manning: Sperm, Sperm, Sperm
“The Ratio of 2nd to 4th Digit Length: A Predictor of Sperm Numbers and Concentrations of Testosterone, Luteinizing Hormone and Oestrogen,” J.T. Manning, D. Scutt, J. Wilson and D.I. Lewis-Jones, Human Reproduction, vol. 13, no. 11, November 1998, pp. 3000–4.

Manning: Reproductive Success
“The 2nd:4th Digit Ratio, Sexual Dimorphism, Population Differences, and Reproductive Success. Evidence for Sexually Antagonistic Genes?”, J.T. Manning et al, Evolution and Human Behavior, vol. 21, no. 3, May 1, 2000, pp. 163–83.  Professor Manning explains:

We report data on the following. (a) reproductive success and 2D:4D from England, Germany, Spain, Hungary (ethnic Hungarians and Gypsy subjects), Poland, and Jamaica (women only). Significant negative associations were found between 2D:4D in men and reproductive success in the English and Spanish samples and significant positive relationships between 2D:4D in women and reproductive success in the English, German, and Hungarian samples. The English sample also showed that married women had higher 2D:4D ratios than unmarried women.

Manning: Male Homosexuality
“The Ratio of 2nd to 4th Digit Length and Male Homosexuality,” S.J. Robinson and J.T. Manning, Evolution and Human Behavior, vol. 21, no. 5, September 1, 2000, pp. 333–345. Professor Manning reports:

We report that (a) 2D:4D was lower in a sample of 88 homosexual men than in 88 sex- and age-matched controls recruited without regard to sexual orientation, (b) within the homosexual sample, there was a significant positive relationship between mean 2D:4D ratio and exclusive homosexuality, (c) overall, there was a decrease in 2D:4D from controls to homosexual men to bisexual men.

***

Emma Nelson, Student of the Fingers of Early Man
Emma Nelson, a graduate student at the Unversity of Liverpool, has done a series of finger-related studies, some with John T. Manning, others with others. Here are two of the most salient.

Nelson: Sex Cave Art Hand Stencils
“Using the Length of the 2nd to 4th Digit Ratio  (2D:4D) to Sex Cave Art Hand Stencils: Factors to Consider,” E. Nelson, J. Manning and A. Sinclair, Before Farming, vol. 1, 2006, pp. 1–7.

Nelson: Chimp Testes Size and Dominance
“The Length of the 2nd to 4th Digit Ratio (2D:4D), Testes Size and Dominance in a Group of Captive Chimpanzees (Pan troglodytes),” E.C. Nelson, E. Videan and S. Shultz. This study is not yet published, but can be found online.

***

(Image credit: Archanapatil215)

Martin Voracek, Scholar of Manly Fingers
Martin Voracek of the University of Vienna takes a manifold interest in fingers. He has collaborated
with finger research celebrity John T. Manning, and done other research independently. Dr. Voracek’s work on this and many other subjects was featured in the special Rivalry issue of AIR (vol. 13, no. 3).  Here we mention his finger work but briefly.

Voracek: Danish Men and How to Measure Them
“High (Feminized) Digit Ratio (2D:4D) in Danish Men: A Question of Measurement Method?”, M. Voracek and S.G. Dressler, Human Reproduction, vol. 21, 2006, pp. 1329–31.

Voracek and Manning: Austrian Men and Their Conquests
“Digit Ratio (2D:4D) in Homosexual and Heterosexual Men from Austria,” M. Voracek, J.T. Manning and I. Ponocny, Archives of Sexual Behavior, vol. 34, 2005, pp. 335–40.

Voracek and Manning: Austrian and German Men and Their Conquests

“2nd to 4th Digit Ratio (2D:4D) and Number of Sex Partners: Evidence for Effects of Prenatal Testosterone in Men,” Johannes Honekopp, Martin Voracek and John T. Manning, Psychoneuroendocrinology, vol. 31, 2006, pp. 30–7.

We report two studies concerning the relationship between a probable negative correlate of prenatal testosterone, the ratio of the length of 2nd and 4th digits (2D:4D), and number of sexual partners per individual (NSP) in men... We tested [our hypothesis] in two samples of men: (a) German heterosexual males recruited from a University and from the general population; (b) Austrian heterosexual and homosexual men recruited from offices and social clubs in Vienna.

The relationship between number of sexual partners and 2D:4D appears to be confined to heterosexual men.

Voracek: Mice and Men
“Of Mice And Men—Cross-Species Digit Ratio (2D:4D) Research: Comment on Bailey, Wahlsten, and Hurd (2005),” M. Voracek, Genes, Brain and Behavior, vol. 5, 2006, pp. 299. (For the original article upon which Professor Voracek is commenting, as well as the original authors’ reply to his comment, see the below section on Peter Hurd.)

Voracek: Fingers and Fencing
“Digit Ratio (2D:4D), Lateral Preferences, and Performance in Fencing,” M. Voracek, B. Reimer, C. Ertl and S.G. Dressler, Perceptual and Motor Skills, vol. 103, 2006, pp. 427–46.

Voracek and Manning: Fingers and Penis
“Length of Fingers and Penis are Related Through Fetal Hox Gene Expression,” M. Voracek and J.T. Manning, Urology, vol. 62, 2003, p. 201.

Voracek: Thumbs
“Sex and Side Differences in Relative Thumb Length,” M. Voracek, Journal of Hand Surgery, vol. 31, 2006, pp. 326–7.

***

Marc Breedlove, Discoverer of Lesbian Finger Distinctions
S. Marc Breedlove is Barnett Rosenberg Professor of Neuroscience at Michigan State University. He has become a giant of finger research. Here are two of his most heralded studies.

Breedlove: Sexual Orientation and Fingers
“Finger-Length Ratios and Sexual Orientation,” Terrance J. Williams, Michelle E. Pepitone, Scott E. Christensen, Bradley M. Cooke, Andrew D. Huberman, Nicholas J. Breedlove, Tessa J. Breedlove, Cynthia L. Jordan, and S. Marc Breedlove, Nature, vol. 404, no. 6777, March 30, 2000, pp. 455–6.
(Thanks to Mason Porter et al for bringing this to our attention.) Professor Breedlove reports a wealth of information:

Among heterosexuals, the mean 2D:4D ratio is larger in women than in men, especially on the right hand. The right-hand 2D:4D ratio of homosexual women is more masculine (that is, smaller) than that of heterosexual women. Men with more than one older brother are more likely to be homosexual and have a significantly more masculine right-hand 2D:4D ratio than men without older brothers. Subjects were offered lottery ‘scratcher’ tickets for their participation.

Breedlove: Lesbian Fingers at a Street Fair
“Differences in Finger Length Ratios Between Self-identified ‘Butch’ and ‘Femme’ Lesbians,” W.M. Brown, C.J. Finn, B.M. Cooke and S.M. Breedlove, Archives of Sexual Behavior, vol. 31, 2002, pp. 117–121.

We surveyed individuals from a gay pride street fair and found that lesbians who identified themselves as “butch” had a significantly smaller 2D:4D than did those who identified themselves as “femme.”

***

Peter Hurd, Seeker of Hockey Players and Depressed Men
Peter Hurd is Associate Professor of Psychology at the University of Alberta. He is a prolific finger-length researcher. A March 3, 2005 press release from the university says: Hurd is conducting ongoing research in this area, including a study that involves measuring hockey players’ finger lengths and cross-referencing the results with each player’s penalty minutes. Here are two of his most celebrated studies.

Hurd: Inbred Mouse Strains
“Digit Ratio (2D:4D) and Behavioral Differences Between Inbred Mouse Strains,” A. A. Bailey, D. Wahlsten and P. L. Hurd, Genes, Brain and Behavior, vol. 4, no. 5, July 2005, pp. 318–23.

Hurd: Depressed Men
“Depression in Men Is Associated with More Feminine Finger Length Ratios,”  Allison A. Bailey and Peter L. Hurd, Personality and Individual Differences, vol. 39, pp. 829–36.

Hurd: Nay, Nay, Voracek, Not in Mice
“No Sex Difference In Mouse Digit Ratio: Reply to Voracek (letter),” D. Wahlsten and P.L. Hurd, Genes, Brain and Behavior, vol. 5, pp. 300–2.

***

Mark Brosnan, Examiner of Scholars’ Fingers
Dr. Mark Brosnan is a psychology researcher at the University of Bath, and a noted comparative-digit-length scholar. On his web site, Dr. Brosnan reports an array of discoveries he made by studying 100 of his colleagues at the university. In his words:

Digit ratio is significantly different between:

Members of the Science Faculty and members of the HaSS/Management Faculty

Those with children and those without children

Those with children who have a psychological diagnosis in the family (typically Dyslexia) and those with children who do not have a psychological diagnosis in the family.

Digit ratio is NOT significantly different between:

Males and females
 
Lecturers, Senior Lecturers, Readers and

Professors

Left and right handers

Dr. Brosnan wrote a study, soon to be published (in 2008), about finger ratios and mathematical ability. In it, he explains:

Recent research has identified a relationship between digit ratio and basic numeric competency.... The present study extended this finding to academic assessment, namely the Standardised Assessment Tests undertaken in numeracy and literacy by children in the UK at the age of 7.... Digit ratios were calculated for 75 (mainly Caucasian) children aged between 6 and 7 attending a state funded infant school. The digit ratios were then correlated with the results from their national standard assessment tests (SATs). A significant correlation was found as hypothesised.... These effects were small.

***

Siegfried Dewitte and Bram Van den Bergh, Finger Financialists
Professor Siegfried Dewitte is an applied economist at Katholieke Universiteit Leuven. Bram Van den Bergh trained under Professor Dewitte. They are rising stars in comparative-finger-length explication. Their work, compared with that of some of their competitors, is abstruse. Here are the two best-known of their publications.

Dewitte: Fingers and Cooperation
“Second to Fourth Digit Ratio and Cooperative Behavior,” K. Millet and S. Dewitte, Biological Psychology, vol. 71, no. 1, 2006, pp. 111-115. The authors explain:

[We] predicted that a low 2D:4D would be associated with high levels of egoism and altruism and low levels of common cooperativeness (i.e. contributing exactly one’s fair share). We found the exact opposite: participants with a low 2D:4D were more likely to act cooperatively and less likely to act altruistically and egoistically.
 

Dewitte and Van den Bergh: Fingers and Ultimatums
“Digit Ratio (2D:4D) Moderates the Impact of Sexual Cues on Men’s Decisions in Ultimatum Games,” Bram Van den Bergh and Siegfried Dewitte,  Katholieke Universiteit Leuven Working Paper No. MO 0604, 2006. The authors write:

Three experimental studies demonstrate that ‘sex-related cues’ impact human decision-making in ultimatum games [games in which the players must split a pot of money amongst themselves]. Our studies show that exposure to pictures of sexy women or lingerie increases the likelihood of accepting unfair offers. Digit ratios of responders are reliably associated with their behaviour: males with lower digit ratios are more likely to reject an unfair split in neutral contexts, but more likely to accept unfair offers in sex-related contexts.

_____________________

This article is republished with permission from the September-October 2007 issue of the Annals of Improbable Research. You can download or purchase back issues of the magazine, or subscribe to receive future issues. Or get a subscription for someone as a gift! Visit their website for more research that makes people LAUGH and then THINK.


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