Bull. Natl. Mus. Nat. Sci., Ser. D, 43, pp. 1–6, December 22, 2017

Sexual dimorphism in the human hand proportion:
A radiographic study
Megumi Kondo1, Naomichi Ogihara2, Ken-ichi Shinoda3, Sayaka Anada1, Kohta Ito2,
Mitsunori Murata4, Toshiaki Tanaka5, Shozo Takai6 and Shuji Matsuʼura1
1
2

Laboratory of Physical Anthropology, Ochanomizu University, Bunkyo Ward, Tokyo 112–8610, Japan
Department of Mechanical Engineering, Keio University, Yokohama City, Kanagawa 223–8522, Japan3
Department of Anthropology, National Museum of Nature and Science,Tsukuba City, Ibaraki 305–0005, Japan
4
Wayo Womenʼs University, Ichikawa City, Chiba 272–8533, Japan
5
Tanaka Growth Clinic, Yoga 2–36–7, Setagaya Ward, Tokyo 158–0097, Japan
6
University of Tsukuba, Tsukuba City, Ibaraki 305–8577, Japan

Abstract The proportion of the human hand, i.e., the length relationships between the fingersand palm, is known to differ between males and females. However, sexual dimorphism in the proportions of individual metacarpals and phalanges has not been investigated in detail. In the presentstudy, we analyzed patterns of variability in the human hand in a modern Japanese population
based on planar radiography. A total of 197 anteroposterior X-ray images of the adult hand wereobtained. The lengths of 19 metacarpals and phalanges were measured by digitizing the images.
Variation patterns in hand proportions were extracted and compared based on a principal component analysis. Our results demonstrated that males have significantly longer metacarpals and phalanges than females. Furthermore, there is a significant difference in hand proportion between
males and females, with males having relatively longer distal phalanges among finger bones. Also
males have relatively shorter second but relatively longer fourth fingers than females. This indicates that hand bone dimensions could possibly be used as a good indicator of sex. We also foundthat individuals with relatively longer fingers tend to possess relatively shorter metacarpal lengths
and vice versa, but this tendency was not associated with sex. Our results may be useful for understanding normal growth of hand proportions and in designing gender-specific hand tools.
Key words: Sexual dimorphism, Metacarpals and phalanges, Length relationships, Human hand
proportion, Planar radiography

Introduction
The proportion of the human hand, i.e., thelength relationships between the fingers andpalm, is known to differ between males andfemales. For example, it has been historicallyknown that males tend to have relatively shorter
second but longer fourth digits than females(e.g., Baker, 1888; George, 1930; Peters et al.,
2002; Robertson et al., 2008), possibly due toprenatal hormonal environment (Putz et al.,
2004; Honekopp et al., 2007; Zheng and Cohn,
2011; Klimek et al., 2016). Furthermore, previous studies have reported that the length data ofhand bones can be used for sex determination(Case and Ross, 2007), indicating that there is acertain degree of sexual dimorphism in the proportion of the human hand. However, we areaware of no previous studies that have systematically analyzed sexual dimorphism in the patternsof correlation and covariation among the lengthsof all individual metacarpals and phalanges. Thismay be the case mainly due to the difficulty ofcollecting hand bone length data. Therefore,
detailed patterns of sexual dimorphism in thehuman hand proportion have remained unclear.
In the present study, based on planar radiography, we analyzed patterns of variability of theKondo et al.

2

human hand proportion among individuals of amodern Japanese population. Specifically anteroposterior X-ray images of modern Japanese adulthands were obtained, and the lengths of all 19
metacarpals and phalanges were measured. We
aimed to analyze the pattern of variations in thehand proportion based on a principal componentanalysis. By using the X-ray images, bonelengths could be directly measured with highprecision, hopefully extracting unknown sexual
differences in hand proportions.
Several previous studies have measured themetacarpal and phalangeal bone lengths fromplanar radiographs to analyze the relative lengthsof the bones (Hamilton and Dunsmuir, 2002;
Park et al., 2003). However, the aim of thesestudies was to test if the bone lengths of thehuman hand correlated with the Fibonaccisequence (Littler, 1973), and not to clarify sexual
differences in the human hand proportion.
Materials and Methods
In the present study, we used anteroposterior
X-ray images of the right hands of a total of 197
adult individuals (61 males and 136 females)
who participated in the Ogi Growth Study performed by the Saga University School of Medicine from 1979 to 1988 (Takai, 1990; Takai andShinoda, 1991). This study was a longitudinal
growth study of Japanese students who resided inOgi city, Saga prefecture, Japan. Along withstandard anthropometric measurements, ananteroposterior X-ray image of the right hand
was taken every year from the age of 6 to 18years (all the X-ray films are currently housed inthe Department of Anthropology, National
Museum of Nature and Science). In the present
study, we selected only the X-ray images (anonymized in an unlinkable fashion) after epiphyseal
fusion since our focus was on the adult hand proportion.
The X-ray films were scanned with the resolution of 150 dpi (a pixel size of 0.169 mm) using afilm scanner (EPSON GT-X980). On each digital
image, the most proximal and distal ends ofFig. 1. Anteroposterior X-ray image of the handwith some digitized points connected by line
segments representing bone lengths.

metacarpals (MC), proximal phalanges (PP),middle phalanges (MP), and distal phalanges(DP) were manually digitized along the shaftaxis (Figure 1). This was done using custommade software named Dicom&16Tiff Viewer
Ver.2.2 (Ogihara Lab., Dept. Mech. Eng., Keio
University). Using this program, we calculated
the distances between the proximal and distal
ends of the bones. The measurement was conducted by one of the authors (S.A.). Each length
was measured twice (on different days), and themean value was used as the length of each MC orphalanx. The intra-observer error of the length
measurement was approximately 0.3 mm for all
the bones, corresponding to ＜1% of the lengthof the MCs and PPs, and ＜2% of the MPs andDPs, indicating that the measurements weremade in a highly reproducible fashion.
In the present study, hand proportion variation
among individuals were examined by computing

Sexual dimorphism in human hand proportion

the principal components (PCs) from the variance-covariance matrix of 19 hand bone dimensions (lengths) using R version 3.2.4 (The R
Project for Statistical Computing). To extractpossible size-related change of hand proportions,correlations between the PC scores and the log ofthe stature of the participant (at the time of radiography) were tested. In order to test for significant differences in PC scores between females
and males, one-way analysis of variance(ANOVA) was conducted using the same software.
The present study was approved by the Ethics
Committee of the National Museum of Natureand Science.
Results
The means and standard deviations of themeasured metacarpal and phalangeal bonelengths are presented in Table 1. The results of
PCA concerning variability in hand proportionsof the modern Japanese population are presented
in Figure 2 as plots of the first principal component (PC1) versus PC2, and as PC1 versus PC3.
Based on a scree plot and cumulative variance,
we considered the first three principal components to be dominant and thus retained them forfurther analyses. The remaining components
were interpreted as secondary components show-3

ing scarce morphological variation as represented in the hand proportion. The first three PCs
accounted for 92.5% of the variation (85.4%,4.9%, and 2.2% for PC1, PC2, and PC3, respectively).
Only PC1 exhibited a significant positive linear relationship with log stature (r＝0.781,p＜0.001). Plots of the PC scores in Figure 2
showed clear separation between female andmale hands along the PC1 axis, indicating that
Table 1. Mean values and standard deviations ofmetacarpal and phalangeal bone lengths (mm)Male (n=61)
MC1MC2MC3MC4MC5PP1PP2PP3PP4PP5MP2MP3MP4MP5DP1DP2DP3DP4DP5Female (n=136)

MeanSD

MeanSD

48.3
71.0
66.7
59.9
55.0
32.6
42.9
47.9
44.8
35.023.8
28.6
27.2
18.5
22.4
17.9
19.2
20.0
17.6

3.1
4.7
4.3
3.7
3.4
2.4
2.7
2.9
2.7
2.2
1.7
1.9
1.8
1.7
1.8
1.3
1.3
1.4
1.5

43.4
64.4
60.7
54.6
50.0
29.2
39.4
43.9
40.8
31.9
21.7
26.1
24.6
16.3
19.8
15.9
17.0
17.5
15.6

2.7
3.6
3.5
3.2
3.1
1.9
2.2
2.4
2.2
1.9
1.5
1.6
1.6
2.1
1.7
1.1
1.2
1.2
1.2

Fig. 2. The results of principal component (PC) analysis. Left, PC1 (x-axis) versus PC2 (y-axis); right, PC1(x-axis) versus PC3 (y-axis). Red circle, female; blue triangle, male.

Kondo et al.

4size-related variation due to sexual dimorphism
is represented by PC1. Significant differences of
PC1 scores between the sexes were detected by
ANOVA (p＜0.001). Besides PC1, there was asignificant sexual difference only in PC3 (Figure2), with males tending to have slightly higher
PC3 sores (p＜0.01).
The factor loadings of each PC axis were presented in Figure 3. Figure 3 demonstrates thatwith increasing PC1 values, all 19 bones tend tobe longer, indicating that the variation represented
by PC1 is mostly size-related. On the other hand,PC2 represents relative elongation of all the phalanges and a relative contraction of MC2-5 withincreasing PC2 values. It is interesting to noteFig. 3.

that the PC2 loadings of the four MPs were muchgreater than those of the PPs and DPs.
PC3 represents relative elongation of the DPs
and a relative contraction of MPs with increasing
PC3 values. The PC3 factor loading was noticeably high in the DP1, suggesting that males tend
to possess relatively long DPs, particularly in thethumb. We also note that the factor loadings ofthe MPs tended to decrease (more negative) withdistance from MP2.
Discussion
The present study analyzed possible statisticaldifferences between male and female hand pro-Factor loadings for the 19 hand bones.

Sexual dimorphism in human hand proportion

portions using 19 metacarpal and phalangeal
bone dimensions. To our knowledge, this is thefirst study to apply a multivariate statistical analysis to identify sexual differences in the human
hand proportion. From the results of the presentstudy, we have demonstrated that the DPs, particularly that of the first ray, are relatively longer inmale phalanges than in female phalanges. Thechange in phalangeal proportion might be related
to the grasping capability of the hand. The difference in the relative lengths of the three phalanges
may alter kinematics and force-generating capacity of the fingers and thumb, possibly leading to achange in grasping capability of the hand. However, the is also a possibility that the change inphalangeal proportion might simply emerge due
to differences in the timing of secondary sexual
development and fusion of epiphysis, but has
nothing to do with the functional difference ofthe hand between males and females. The functional significance of this difference in hand proportion between males and females should beinvestigated in future studies.
It is well established that males tend to haverelatively shorter second but longer fourth digits
than females (e.g., Baker, 1888; George, 1930;
Peters et al., 2002; Robertson et al., 2008). In ouranalysis, this was observed in the factor loadingsof the PC1 presented in Figure 3. If we compared
the factor loadings of PPs, MPs and DPs between
the second and fourth fingers, the values werealways larger in the fourth finger. The PC1 score
was significantly larger in the male hands than infemale hands. Therefore, our result is consistent
with the previous findings reporting that males
tend to have relatively shorter second but relatively longer fourth fingers than females. Thistendency was also confirmed by the fact that
there was a significant difference (p＜0.01) inthe ratio between the second and fourth digit
lengths (PP ＋ MP ＋ DP) between males andfemales using the same sample.
We also found that there is a certain trend invariability of hand proportions that is independent of both size and sex. The human hand tends
to possess relatively short metacarpal bones if

5

the phalangeal bones are relatively long, and viceversa. And if the fingers become relatively long,the MPs tend to get relatively longer than the PPsand DPs. Understanding the pattern of variabilityof hand proportions is important in designinggloves as well as hand tools (Kouchi et al.,2005). The present description of possible patterns of hand proportion variability may be useful in the field of ergonomics.
One limitation of the present study is that wehere studied only the hand of a Japanese population. However, hand proportions are known todiffer geographically (Manning et al., 2004,2007; Loehlin et al., 2006), because of environmental factors such as climate. Studying variability in the hand proportions of different populations is an issue for future research. Anotherlimitation is that we studied the sexual differenceof the hand proportion using adult radiographs,
and did not study ontogenetic changes of proportion. Since longitudinal radiographs of the same
participants are available, in future studies, weplan to investigate the developmental change ofhand proportions by adding the longitudinal data.
Acknowledgement
We wish to express our thanks to anonymous
reviewers for constructive and useful comments
which improved the manuscript, and to the Editor of this journal, Dr. Kazuhiro Sakaue, for hisgenerous help.
References
Baker, F. 1888. Anthropological notes on the human hand.
The American Anthropologist, 1: 51–76.
Case, D. T. and Rose, A. H. 2007. Sex determination fromhand and foot bone lengths. Journal of Forensic Science, 52: 264–270.
George, R. 1930. Human finger types. Automical Record,
46: 199–204.
Hamilton, R. and Dunsmuir, R. A. 2002. Radiographic
assessment of the relative lengths of the bones of thefingers of the human hand. Journal of Hand Surgery(British and Eouropean), 27B: 546–548.
Honekopp, J., Bartholdt, L., Beier, L. and Liebert, A.
2007. Second to fourth digit length ratio (2D : 4D) and6

Kondo et al.

adult sex hormone levels: New data and a meta-analytic review. Psychoneuroendocrinology, 32: 313–321.
Klimek, M., Galbarczyk, A., Nenko, I. and Jasienska, G.
2016. Brief communication: Woman with more feminine digit ratio (2D : 4D) have higher reproductive success. American Journal of Physical Anthropology, 160:
549–553.
Kouchi, M., Miyata, N. and Mochimaru, M. 2005. An
analysis of hand measurements for obtaining representative Japanese hand models. Proceeding of the 8thAnnual Digital Human Modeling for Design and Engineering Symposium, 2005-01-2734: (CD-ROM).
Loehlin, J. C., McFadden, D., Medland, S. E. and Martin,
N. G. 2006. Population differences in finger-length
ratios: ethnicity or latitude? Archives of Sexual Behavior, 35: 739–742.
Manning, J. T., Stewart, A., Bundred, P. E. and Trivers,
R. L. 2004. Sex and ethnic differences in 2nd to 4th
digit ratio of children. Early Human Development, 80:
161–168.
Manning, J. T., Churchill, A. J. and Peters, M. 2007. The
effects of sex, ethnicity, and sexual orientation on selfmeasured digit ratio (2D : 4D). Archives of SexualBehavior, 36: 223–233.
Park, A. E., Fernandez, J. J., Schmedders, K. and Cohen,M. S. 2003. The Fibonacci sequence: relationship to thehuman hand. The Journal of Hand Surgery, 28A: 157–160.
Peters, M., Mackenzie, K. and Bryden, P. 2002. Finger
length and distal finger extent patterns in humans.
American Journal of Physical Anthropology, 177: 209–217.
Putz, D. A., Gaulinb, S. J. C., Sporterc, R. J. and McBurney, D. H. 2004. Sex hormones and finger length What
does 2D:4D indicate? Evolution and Human Behavior,
25: 182–199.
Robertson, J., Zhang, W., Liu, J. J., Muir, K. R., Maciewicz, R. A. and Doherty, M. 2008. Radiographic
assessment of the index to ring finger ratio (2D : 4D) inadults. Journal of Anatomy, 212: 42–48.
Takai, S. 1990. Smoothed skeletal maturity curve of Japanese children by Tanner-Whitehouse 2 (TW2) method
and its application. Kaibogaku Zasshi (Acta Anatomica
Nipponica), 65: 436–447 (In Japanese).
Takai, S. and Shinoda, K. 1991. The mid- and adolescent
growth spurts of some somatic dimensions analyzed bya smoothing cubic B-spline function. Bulletin of Institute of Health and Sport Science, University of Tsukuba, 14: 119–130 (In Japanese).
Zheng, Z. and Cohn, M. J. 2011. Developmental basis ofsexually dimorphic digit ratios. Proceedings of theNational Academy of Sciences, 108: 16289–16294.