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Digit Ratio: A Pointer to Fertility, Behavior, and Health



An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.
Heredity (2002) 89, 403
2002 Nature Publishing Group All rights reserved 0018-067X/02 $25.00
Book review
Digit Ratio: A Pointer to Fertility,
Behavior, and Health
John T Manning
Rutgers University Press, New Jersey. 2002; 173 pp. $27.00,
paperback. ISBN 0-8135-3030-X
Heredity (2002) 89, 403. doi:10.1038/sj.hdy.6800151
The main message of this book is simple and John Man-
ning does an excellent job of delivering it clearly. The
ratio of second and fourth (finger) digit lengths (2D:4D)
appears to be affected by foetal testosterone exposure,
may be fixed before birth, and so may be a reliable indi-
cator of early prenatal conditions and subsequent
health factors.
Through sequential chapters, Manning relates 2D:4D to
various evolutionary concepts such as reproductive suc-
cess, individual performance, heritability, and mate
choice; to social factors such as aggression, sexual prefer-
ences, and individual status; through to more applied
medical studies of health and illness. Clearly, some of
these relationships are better supported than others, and
Manning presents the weakest correlations with a few
well-placed caveats.
In general, the book builds from relatively basic claims
to declarations that many readers will construe as ‘over-
interpretation’. If we take Manning’s conclusions literally,
you could predict a team’s performance at the next World
Cup by the digit ratio of team members (p 139) the
lower 2D:4D the better their chances. This means we
should all head to Ladbrokes and bet on rank outsiders
Jamaica they have the lowest digit ratio of the cultures
sampled so far (p 19), and yet will offer quite stagger-
ing odds!
The book is aimed as an introductory text into this field
and, as such, presents data that has been analysed with
varying statistical rigour. Manning also adopts a fairly
uncritical tone throughout. It is fair to say that several of
the correlations presented have marginal significance,
and r
values and effect sizes are largely not reported.
Many bivariate plots resemble shotgun blasts, and much
of the data are not published. Maybe this will change as
the field grows. Or perhaps we should expect weak corre-
lations when analysing such complex, multidimensional
traits (such as human sexual orientation)?
I was a little surprised at the apparent holes in the data.
It is unclear to what extent 2D:4D is affected by foetal
testosterone, and how much of the variance in the digit
ratio of adults is explained by uterine conditions. Man-
ning reports a lack of longitudinal data on relative
changes in finger lengths with age. Yet several of his own
datasets point to digit ratio differences among age
cohorts (eg, pp 87 and 91). Also, he has previously
reported significant within-individual changes in finger
dimensions over short time periods (Manning et al, 1996;
Scutt and Manning, 1996; Manning et al, 2002). Person-
ally, I am not sure how to reconcile these discrepancies
and it would have been useful for Manning to address
this head-on.
Readers will undoubtedly adopt more welcoming or
more damning views of the book’s thesis. Clearly this is
a field of interest to many health care professionals and
yet some fundamentally important questions remain
unexplored. Manning communicates this well. Every
student entering graduate school in a related field should
be licking their chops! There is plenty to achieve here.
With this in mind, I hope that researchers working in this
field steer clear of wholly adaptive scenarios and adopt
quantitative rigor in interpreting the strengths and weak-
nesses of their data. The field of digit ratio research, and
any medical advances that accrue, will be better for it.
The book is designed to open people’s eyes to possi-
bilities rather than make definitive statements. There is
just too little data at present. Manning’s style is jovial,
easy to read, and will make digit ratio research interest-
ing and accessible to many. This is a great book for stu-
dents to read, but may frustrate many seasoned evol-
utionary biologists. If it is read with the appropriate
caveats in mind, it will be a good basis for seminars and
discussion classes.
Manning JT, Gage AR, Driver MJ, Scutt D, Fraser WD (2002).
Short-term changes in asymmetry and hormones in men. Evol
Human Behav 23: 95–102.
Manning JT, Scutt D, Whitehouse GH, Leinster SJ, Walton JM
(1996). Asymmetry and the menstrual cycle in women. Ethol
Sociobiol 17: 129–143.
Scutt D, Manning JT (1996). Symmetry and ovulation in women.
Human Reprod 11: 2477–2480.
JP Swaddle
Institute for Integrative Bird Behavior Studies
Biology Department
College of William & Mary
Williamsburg VA 23187-8795, USA
... The 2D:4D ratio has been used as a marker in studies of behavioural and psychological characteristics and has even been used to determine an individual's propensity to a range of diseases, especially those diseases that show sex differences in their occurrence, progression and/or prognosis (SWADDLE et al., 2002). ...
... Approximately 19 genes have been correlated to the formation and differentiation of digit ratios and some of them have been correlated to carcinogenesis, making 2D:4D a marker for the action of these genes and predictive of the susceptibility to several types of cancer, such as oral cancer, prostate cancer, breast cancer , gastric cancer and colorectal cancer (SWADDLE et al., 2002;SARODE et al., 2014;MENDES et al., 2016;GONÇALVES et al., 2017;FERREIRA FILHO et al., 2015). ...
... The 2D:4D ratio is a marker for the activity of these genes and it is possible that digital length is also a predictor for the development of oral cancer; this suggests that such a condition might be related to effects of intrauterine exposure to sex hormones (SWADDLE et al., 2002;SARODE et al., 2014). ...
... Más específicamente, la relación 2D:4D viene dada por el balance entre los andrógenos y los estrógenos durante un pequeño espacio temporal del desarrollo embrionario (Zheng & Cohn, 2011). Estudios previos informaron que los andrógenos del útero de la madre podrían estimular el crecimiento 4D, mientras que los estrógenos podrían estar relacionados con el crecimiento del 2D (Manning et al., 2000;Swaddle, 2002). Así, niveles altos de testosterona en el útero, en comparación con los niveles de estrógenos, se relacionan con una ratio 2D:4D baja; por lo que los hombres suelen presentar, ratios 2D:4D más bajos que las mujeres (Fink, Thanzami, Seydel, & Manning, 2006;Hönekopp & Schuster, 2010;Kociuba, Kozieł, Chakraborty, & Ignasiak, 2017;Manning et al., 2000). ...
... Esto puede ser explicado por la corriente que afirma que la ratio 2D:4D no se ve afectada por el crecimiento (McIntyre et al., 2005;Trivers et al., 2006). Concretamente, autores como Manning et al. (2000) o Swaddle (2002) indicaron que el crecimiento prenatal del cuarto dedo estaría estimulado por los andrógenos; mientras que, el segundo dedo lo estaría por los estrógenos. Esto podría explicar que los chicos presenten una ratio significativamente menor que chicas y, ya que, una baja proporción en la ratio 2D:4D, refleja niveles más altos de testosterona en el útero, en comparación con los niveles de estrógenos (Malas et al., 2006). ...
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Introducción: La ratio 2D:4D es el cociente entre la longitud del dedo índice y anular de la mano, asociada al balance entre andrógenos y estrógenos, durante el desarrollo embrionario. Una baja proporción 2D:4D, refleja niveles más altos de testosterona en el útero. Esta medida se ha relacionado con ciertos parámetros de la composición corporal, que podrían ser indicativos de la probabilidad de presentar riesgos para la salud. Objetivos: analizar si existe relación entre la ratio 2D:4D y la composición corporal y explorar las diferencias entre los sexos. Método: Se realizó un estudio observacional y correlacional con 225 adolescentes (108 chicos y 117 chicas), de entre los 12 y 17 años. Se realizaron medidas antropométricas, de composición corporal y la ratio 2D:4D. Resultados: se encontró una relación directa entre la ratio 2D:4D porcentaje de masa grasa (r=,321 y p<,001) y con el IMC (r=,241 y p<,001). Al segmentar por sexo esta correlación solo se encontró en chicas (r=,408, p<,001 y r=,419, p<,001, respectivamente). Además, se encontraros diferencias significativas entre sexos para altura (p=,002), porcentaje de grasa (p<,001) y masa muscular (p<,001), ratio 2D:4D (p<,001). Conclusiones: existe una relación directa de la ratio 2D:4D con el porcentaje de masa grasa y el IMC en adolescentes de Extremadura; es decir, mayores ratios 2D:4D se asocian a mayores porcentajes de grasa e IMC. Además, las chicas presentan mayores ratios 2D:4D y porcentaje de masa grasa, y menor altura y masa muscular en comparación con los chicos.
... Many studies have demonstrated that women have a higher 2D: 4D than men, which is consistent with our findings. In addition, the D R-L or D L-R of 2D: 4D can reveal 2D: 4D asymmetry between the left and right hands [38]. Several reports have suggested that PT influences R2D: 4D and D R-L more than it influences L2D: 4D, and the D R-L of 2D: 4D is negatively correlated with prenatal exposure and sensitivity to testosterone [39]. ...
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Background Cytochrome P450 (CYP) genes are necessary for the production or metabolism of fetal sex hormones during pregnancy. The second-to-fourth digit ratio (2D: 4D) is formed in the early stage of human fetal development and considered an indicator reflecting prenatal sex steroids levels. We explored the association between 2D: 4D and single-nucleotide polymorphisms (SNPs) of CYP. Material/Methods Correlation analysis between 2D: 4D and 8 SNPs, rs2687133 (CPY3A7), rs7173655 (CYP11A1), rs1004467, rs17115149, and rs2486758 (CYP17A1), and rs4646, rs2255192, rs4275794 (CYP19A1), was performed using data from 426 female and 412 male Chinese university students. SNP genotyping was conducted using PCR. Digit lengths were photographed and measured by image processing software. Results rs2486758 (CYP17A1) correlated with left hand 2D: 4D in men (P=0.026), and rs1004467 (CYP17A1) correlated with right hand 2D: 4D in men (P=0.008) and the whole population (P=0.032). In men, allele G rs1004467 decreased right hand 2D: 4D, while allele C of rs2486758 increased left hand 2D: 4D. In women, left hand 2D: 4D was higher in genotypes with allele A of SNP rs4646 (CYP19A1) under the dominant genetic model; female DR-L was higher in genotypes with allele T of rs17115149 (CYP11A1). SNPs rs2687133 (CYP3A7) and rs1004467 (CYP17A1) were significantly correlated with right hand 2D: 4D (P=0.0107). Conclusions SNPs rs1004467 and rs2486758 of CYP17A1 are significant in the relationship between 2D: 4D and CYP gene polymorphisms under different conditions. SNP interactions between CYP genes probably impact 2D: 4D. The correlation between 2D: 4D and some sex hormone-related diseases may be due to the effect of CYP variants on the 2 phenotypes.
... Manning reported that 2D:4D was a biomarker of prenatal steroid exposure, where a low 2D:4D was associated with prenatal high testosterone and low estrogen exposure 23,24 , and showed that the 2D:4D ratio was negatively correlated with circulating androgens in men and was positively correlated with circulating estrogen in men and women 25 . Some scholars speculate that maternal androgen level during pregnancy may promote the growth of offspring 4D, while maternal estrogen level during pregnancy may promote the growth of offspring 2D 26 . The average finger ratio of men is lower than that of women, that is, a ratio < 1 means that the ring finger is longer, which is called the male pattern 22 . ...
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Body image dissatisfaction (BID) is a negative evaluation of personal physical characteristics, including dissatisfaction with body shape, gender, sexual organs, appearance and so forth, and it plays an important role in growth and development. The second-to-fourth digit ratio (2D:4D) is recognized as a putative indicator of intra-uterine testosterone to estrogen ratio exposure, and it has been observed that higher levels of fetal testosterone exposure are associated with a lower 2D:4D. The present paper contributes to a better understanding of the biological underpinnings of BID by analyzing BID and the digit ratio (2D:4D). We found that the 2D:4D was positively related to appearance dissatisfaction in boys with first spermatorrhea, which means that low prenatal androgen exposure may increase boys’ dissatisfaction with their appearance. In girls with breast development being lower than Tanner stage II, their 2D:4D was negatively related to their body shape dissatisfaction, which means that high prenatal androgen exposure may increase girls’ dissatisfaction with their body shape. These results suggest that the prenatal androgen exposure level might play an important role in the body image dissatisfaction of the offspring.
Background: Digit ratio, especially 2D:4D, is hypothesised as a potential biological marker of exposure to intrauterine sex hormones. The aim of this study was to investigate the association between 10 SNPs of sex steroid hormone receptor (SSHR) related genes and 2D:4D. Subjects and methods: 814 college students were randomly selected as research participants. After taking pictures of both hands of the participants, Image Pro Plus (IPP) software was used to measure 2D:4D. ESR1 (rs2228480 and rs3798758), ESR2 (rs944459, rs8006145, rs928554, and rs8018687), GPER1 (rs10269151 and rs12702047), and PGR (rs1042839 and rs500760) were genotyped using multiplex PCR. Results: Females had significantly higher 2D:4D in both hands than male students (p < 0.05), and the R2D:4D of the Han population was significantly higher than that of the Hui population (p < 0.05). The number of females carrying the GPER1 G allele of rs12702047 was significantly higher than that of males (p < 0.05). The L2D:4D in males was significantly different in rs1042839, and the R2D:4D in the Han ethnicity was significantly different in rs3798758. Logistic regression analysis showed that rs12702047 was significantly associated with 2D:4D in both hands (p < 0.05). Conclusions: GPER1 rs12702047 may be involved in the formation of digit ratio by affecting phalanx development in the Chinese population.
Background: The aim of this study was to analyze the relationship between 2D:4D and childhood overweight or obesity, which might indirectly show the role of prenatal hormone in childhood overweight or obesity. Methods: Using stratified cluster sampling approach, a school-based cross-sectional investigation was undertaken among 687 children and adolescents aged 8-15 years. Each participant's index finger (2D) and ring finger (4D) length, height, weight, testosterone, and estradiol levels were measured, and their dietary behaviors, physical and sedentary activities were also surveyed. Results: The prevalence of overweight or obesity among children and adolescents aged 8- and 12-15 years was 36.0% and 25.9%, respectively (P < 0.05). There were no associations between 2D:4D and overweight or obesity in both boys and girls (P > 0.05). However, 2D and multiplying index of digit ratio and length (MIDRL) associated directly with overweight or obesity among boys (OR (95%CI) were 1.45 (1.00, 2.14), 1.46 (1.01, 2.11), respectively), and was indirectly related to overweight or obesity by testosterone (OR were 1.30, 1.26, respectively). Conclusions: In boys, 2D and MIDRL were directly related to overweight or obesity, and indirectly associated with overweight or obesity by testosterone, which suggested that prenatal hormone exposure might associate with overweight or obesity among boys.
Digit ratio (2D:4D) is a biomarker of prenatal hormone exposure levels; this biomarker is negatively related to prenatal androgen exposure and positively related to prenatal estrogen exposure. We investigated the correlation between digit ratio (2D:4D) and blood pressure. A school-based survey of 687 adolescents aged 8–15 years was conducted. The ring finger (4D) and index finger (2D), systolic blood pressure (SBP), diastolic blood pressure (DBP), testosterone, and estradiol levels were measured. Their dietary behaviors and physical and sedentary activity time were surveyed. The results showed the 2D:4D ratio was not significantly related to SBP, DBP, or testosterone in boys and girls. However, it was significantly positively correlated with serum estradiol levels in boys. The 2D, 4D, multiplied index of digit ratio and length (MIDRL) and average of the index finger and ring finger (AIR) were directly related to SBP in both sexes (βs in boys were 4.16, 5.49, 2.95, and 5.25, respectively, P < 0.01; βs in girls were 3.43, 2.71, 3.02, and 3.36, respectively, P < 0.01) and were also indirectly associated with SBP through testosterone (P < 0.05). The 2D, 4D and AIR were indirectly related to DBP in girls through testosterone (P < 0.05). In conclusion, there were direct and indirect associations between finger-length indicators and blood pressure, which implies that prenatal hormone levels might be correlated with blood pressure in children and adolescents.
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This study examines the relationship between prenatal testosterone exposure (PTE) and selection into entrepreneurship. We argue that the relationship between PTE and entrepreneurial intent is positive and mediated by general and domain-specific risk-taking related to financial investment and professional career. Using the second-to-fourth digit ratio (2D:4D) as noninvasive retrospective marker for PTE, we identify two-step mediation effects of PTE on entrepreneurial intent through both general and domain-specific risk-taking. To account for possible socialization-based effects, we control for gender and parental self-employment. Applying ordinary least square regression analyses and structural equation models, we provide empirical evidence for a biological association between 2D:4D and entrepreneurial intent.
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Digit ratio (2D:4D) denotes the relative length of the second and fourth digits. This ratio is considered to be a biomarker of the balance between fetal testosterone (T) and estrogen (E) in a narrow window of early ontogeny. Evidence for this assertion is derived from direct and indirect measures of prenatal hormonal exposure (in experimental animals, via amniotic fluid samples and in the study of sex-typical traits) in relation to 2D:4D. In contrast, the relationships between 2D:4D and levels of sex steroids in adults are less clear, as many correlational studies of 2D:4D and adult sex steroids have concluded that this association is statistically non-significant. Here, we suggest that in order to understand the link between 2D:4D and sex hormones, one must consider both fetal organizing and adult activating effects of T and E. In particular, we hypothesize that 2D:4D correlates with organizing effects on the endocrine system that moderate activating effects in adulthood. We argue that this is particularly evident in "challenging" conditions such as aggressive and sexual encounters, in which individuals show increased levels of T. We discuss this refinement of the 2D:4D paradigm in relation to the links between 2D:4D and sports performance, and aggression.
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Women have cryptic ovulation, and self-observation methods of determining the timing of ovulation, such as monitoring cervical mucus symptoms or recording basal body temperature, are not reliable. It has recently become apparent that the symmetry of paired soft tissue traits, such as breast size and digit length, changes across the menstrual cycle. This paper presents evidence that symmetry in four paired soft tissue traits showed a marked increase on the day of ovulation. The difference (i.e. the asymmetry) between the size of the left and right trait in ears, 3rd, 4th and 5th digits was measured. The timing of ovulation was confirmed by real-time pelvic ultrasonography and trait measurements were made without knowledge of scan results. Asymmetry was lowest on the day of ovulation (day 0), decreasing by about 30% from day −1, and significant within-subjects changes occurred from days −2 to day −1, and day −1 to day 0. The practical and evolutionary implications of these findings are discussed.
Full-text available
Women have cryptic ovulation, and self-observation methods of determining the timing of ovulation, such as monitoring cervical mucus symptoms or recording basal body temperature, are not reliable. It has recently become apparent that the symmetry of paired soft tissue traits, such as breast size and digit length, changes across the menstrual cycle. This paper presents evidence that symmetry in four paired soft tissue traits showed a marked increase on the day of ovulation. The difference (i.e. the asymmetry) between the size of the left and right trait in ears, 3rd, 4th and 5th digits was measured. The timing of ovulation was confirmed by real-time pelvic ultrasonography and trait measurements were made without knowledge of scan results. Asymmetry was lowest on the day of ovulation (day 0), decreasing by about 30% from day -1, and significant within-subjects changes occurred from days -2 to day -1, and day -1 to day 0. The practical and evolutionary implications of these findings are discussed.
Asymmetries are negatively associated with developmental precision. However, asymmetries in human traits, which consist partly or entirely of soft-tissue, are correlated with a surprising diversity of fitness domains, including fertility, disease resistance, running speed, aggression, and depression. We show that in men there are both between-subject differences in asymmetry and short-term (24 h) within-subject changes in soft-tissue asymmetry, and the latter are more pronounced in some subjects than in others. A number of hormones showed significant correlations with these changes, including positive associations between asymmetry and luteinising hormone (LH), total thyroxine (T4), and parathyroid hormone (PTH), and negative associations between asymmetry and follicle stimulating hormone (FSH). “Fixed” asymmetries accumulated during development represent long-term developmental imprecision and are related to various stressors. Nonfixed asymmetries in soft-tissue traits may correlate with short-term changes in hormone concentrations. We discuss the implications of our findings for the understanding of the relationships between asymmetry, behaviour, and fitness in men, and the possible patterns of short-term changes in asymmetry in male and female partners.
Fluctuating asymmetry (FA) is small random deviations from perfect bilateral symmetry that are thought to accumulate during development. FA is therefore a measure of one component of fitness, that is, developmental stability. This work is not concerned with permanent between-individual differences in asymmetries but rather with temporary within-individual changes in asymmetry that are related to the menstrual cycle (cyclical asymmetry, CA). We present evidence from studies of non-sexually selected traits (ear and digit size) and a sexually selected trait (breast size) that, in characters made up wholly or in part of soft tissue, CA varies across the menstrual cycle in women. It is highest at the beginning and end of the cycle, when women are generally infertile, and low in mid-cycle, when fertility is highest. Furthermore in mid-cycle there is an indication of a transitory (24-hour) increase in CA followed by a substantial decrease, which may indicate ovulation. Temporal changes in CA could therefore be used by males to indicate a female's position in the cycle. We discuss these findings in relation to (1) our understanding of the evolution of human mating systems, (2) the practical implications of these data in the treatment of infertility and to facilitate contraception, and (3) their relevance to exercise and dieting as a means to minimize across-cycle increases in asymmetry.