Second to fourth digit ratio, body mass index, waist-to-hip
ratio, and waist-to-chest ratio: their relationships in
heterosexual men and women
B. Finky, N. Neavez and J. T. Manning}
yLudwig-Boltzmann Institute for Urban Ethology, University of Vienna, Austria
zHuman Cognitive Neuroscience Unit, School of Psychology and Sport Sciences,
Northumbria University, Newcastle upon Tyne, UK
}Department of Psychology, University of Central Lancashire, Preston, UK
Received 26 September 2002; in revised form 20 August 2003; accepted 27 August 2003
Summary. Background: Prenatal sex steroids have been broadly discussed in terms of their
possible effect on brain differentiation, whereas pubertal/adult sex hormones are thought to
be the main regulators of sexually dimorphic physical features in males and females. Asses-
sing prenatal steroid exposure has previously been difficult but evidence now suggests that
finger length ratio may provide a ‘window’ into prenatal hormone exposure. The length of
the second digit (the index finger) relative to the length of the fourth digit (the ring finger) is
sexually dimorphic as males have a lower second to fourth digit ratio (2D:4D). The sexual
dimorphism is determined as early as the 14th week of fetal life, and remains unchanged at
puberty. There is evidence that sex differences in 2D:4D arise from in utero concentrations of
sex steroids, with a low 2D:4D (male typical ratio) being positively related to prenatal
testosterone, while a high 2D:4D (female typical ratio) is positively associated with prenatal
oestrogen.
Aim: The studied aimed to determine whether, and to what extent, adult sexually dimorphic
physical traits, which are largely determined at puberty, relate to traits that are largely
determined in utero. This work examined the relationship between three sexually dimorphic
traits—body mass index (BMI), waist-to-hip ratio (WHR) and waist-to-chest ratio
(WCR)—and digit ratio.
Participants and methods: BMI, WHR and WCR were assessed in 30 heterosexual male and
50 heterosexual female participants by recording their body height, weight, and measuring
their waist, hip and chest circumference. Digit lengths of the second and fourth fingers
were measured from photocopies of the ventral surface of the hand and by actual finger
measurements.
Results: Digit ratio was found to be significantly lower in men than in women. Significant
negative correlations were found between female’s left and right hand 2D:4D, waist and hip
circumference, and WCR. In males, BMI was found to be positively related to digit ratio but
remained significant only for left hand 2D:4D. Generally, the relationships were stronger for
females than for males. Although not all relationships were found to be significant, they
were in accord with our predictions.
Conclusion: In addition to an activational effect of sex hormones at puberty, the present data
suggest an early organizational effect of sex hormones through the association between
indices of female body shape, male BMI, and human finger length patterns.
1. Introduction
In general, females have twice as much body fat as males and this is distributed
differently around the body. Body fat distribution is sexually dimorphic, and while
the dimorphism in body fat is minimal in infancy, childhood and old age, it is maxi-
mal during early reproductive life mediated by sex steroids in combination with
heritable genetic factors (Nelson et al. 1999). During puberty, males deposit adipose
(and also muscle) tissue around the upper body whilst females deposit adipose tissue
around the thighs and buttocks. This distribution of body fat is thought to signal
ANNALS OF HUMAN BIOLOGY
NOVEMBER–DECEMBER 2003, VOL. 30, NO. 6, 728–738
Annals of Human Biology ISSN 0301–4460 print/ISSN 1464–5033 online # 2003 Taylor & Francis Ltd
http://www.tandf.co.uk/journals
DOI: 10.1080/03014460310001620153

the ratio of pubertal/adult oestrogen to testosterone, since the predominance of
oestrogen at puberty produces a typical female body shape (gynoid), while the pre-
dominance of testosterone produces a typical male (android) body shape (Bjorntrop
1997).
The main reason for the stability of sexual dimorphism of body mass index
(BMI), waist-to-hip ratio (WHR) and waist-to-chest ratio (WCR) is the sex-hormone
profile of an individual. For example, low WHR in women is typically associated
with high levels of circulating oestrogens, whereas high WHR is correlated with high
levels of circulating testosterone (Evans et al. 1983). WHR in females appears to be
directly linked to health and fertility as it has been shown to be an accurate predictor
of risk for various diseases (e.g. Singh 1994, Abbott et al. 2002). Moreover, females
with an optimal WHR produce more offspring and become pregnant more rapidly
when receiving artificial insemination (Singh and Zambarano 1997). Drawings of
female figures with a WHR of around 0.7 are rated as being more healthy and fertile
(Singh 1993) though this is not always reported (Furnham et al. 1997). Some recent
studies have, however, suggested that BMI might be equally or more closely related
to female fertility, attractiveness and health (Tove´e et al. 1998). A BMI of around 19
is associated with better health and higher reproductive capability (Willett et al.
1995, Wang et al. 2000).
Evidence for exogenous sex hormone administration on body fat distribution can
be observed in transsexual men and women. Men that were treated with oestrogen
developed a gynoid fat distribution, whereas women treated with testosterone devel-
oped an android fat distribution (Vague et al. 1984). Studies have shown that in
normal males, ageing is accompanied by decreasing testosterone levels, decreasing
lean body mass and increasing abdominal fat deposition. Testosterone supplemen-
tation in elderly males and in healthy eugonadal men decreases WHR and increases
lean body mass (Rebuffe-Scrive et al. 1991, Vermeulen et al. 1999).
It is commonly accepted that pubertal/adult sex hormones are the main regulators
of sexually dimorphic physical features. However, some studies have suggested that
early (prenatal) hormones may also significantly influence the development of
somatic asymmetries. Sexually dimorphic physical traits are mainly interpreted as
a consequence of pubertal hormone levels but at least part of the variance in these
traits may depend upon in utero masculinizing or defeminizing effects. However, the
interplay between organizational and activational effects of hormones is still a matter
of debate. Hence are, and to what extent, sexually dimorphic traits, largely deter-
mined at puberty, related to traits that are largely determined in utero?
One physical feature that has been suggested to relate to prenatal hormone levels
is the ratio between the length of the second digit (the index finger) and the length of
the fourth digit (the ring finger). There is accumulating evidence that this 2D:4D
ratio is sexually dimorphic and is largely determined prenatally (Manning 2002).
Thus males tend to show lower values of 2D:4D than do females, i.e. males have
on average longer fourth digits relative to their second than females (Phelps 1952,
Manning et al. 1998). Relative finger lengths are determined before birth (Garn et al.
1975), the sex difference in 2D:4D is present in children as young as 2 years
(Manning et al. 1998), and sex differences in 2D:4D are robust across a number of
ethnic groups and races (Manning 2002).
The sexual dimorphism in 2D:4D has been known for many years (e.g. see Baker
1888). However, it has only recently been suggested that sex differences in 2D:4D
arise from in utero concentrations of sex steroids, with 2D:4D negatively related to
Digit ratio and body shape 729