Evolution and Human Behavior 21 (2000) 1–9
Original articles
Second to fourth digit ratio in elite musicians: Evidence for
musical ability as an honest signal of male fitness
Vanessa A. Sluming M.Sc.a, John T. Manning, Ph.D.b,*
a
Department of Medical Imaging and the bSchool of Biological Sciences, The University of Liverpool,
Liverpool, United Kingdom
Manuscript received September 13, 1999; revised manuscript September 20, 1999
Abstract
Prenatal testosterone may facilitate musical ability. The ratio of the length of the second and fourth
digit (2D:4D) is probably determined in utero and is negatively related to adult testosterone concentrations and sperm numbers per ejaculate. Therefore, 2D:4D may be a marker for prenatal testosterone
levels. We tested the association between 2D:4D and musical ability by measuring the ratio in 70 musicians (54 men and 16 women) recruited from a British symphony orchestra. The men had significantly lower 2D:4D ratios (indicating high testosterone) than controls (n ⫽ 86). The mean 2D:4D of
women did not differ significantly from controls (n ⫽ 78). Rankings of musical ability within the orchestra were associated with male 2D:4D (high rank ⫽ low 2D:4D). Differences in 2D:4D ratio were
not found among instrument groups, suggesting that 2D:4D was not related to mechanical advantages
in playing particular intruments. Concert audiences showed evidence of a female-biased sex ratio in
seats close to the orchestra. This preliminary study supports the thesis that music is a sexually selected
trait in men that indicates fertilizing capacity and perhaps good genes. However, the association between low 2D:4D ratio and orchestra membership and high status within the orchestra may result from
testosterone-mediated competitive ability. Further tests of the association between 2D:4D and musical
ability per se are necessary. © 2000 Elsevier Science Inc.
Keywords: Second to fourth digit ratio; Musicians; Signal; Fitness
The production of music takes time and energy and apparently has no adaptive value in
surviving predation or infection or in obtaining food. However, this commonsense observation does not preclude a Darwinian explanation for the existence of music. Darwin (1871)
himself argued that human music, along with bird song, was explicable in terms of sexual selection. More recently, Miller (1998, 1999) pointed out that parallels between human music
and bird song, gibbon song, and whale song support a biological interpretation of music as
* Corresponding author. E-mail: [email protected].
1090-5138/00/$ – see front matter © 2000 Elsevier Science Inc. All rights reserved.
PII: S1 0 9 0 - 5 1 3 8 ( 9 9 ) 0 0 0 2 6 -4
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sexual courtship. Among classical and popular musicians, males are more common than females. An inspection of the web sites of 18 symphony orchestras (5 British, 9 Continental
European, and 4 North American orchestras) revealed a male representation varying from
60% to 97% (mean 80%). Consistent with this, Miller (in press) showed that principal musicproducers of more than 7,000 jazz, rock, and classical albums were predominantly males
(male to female ratio of 10:1) whose musical output peaked at around age 30. A similar pattern in human homicide has been reasonably accepted as evidence for the importance of sexual selection in the evolution of violent competition (Daly and Wilson, 1994). Of course, we
are not arguing that females are unable to appreciate or produce music. On the contrary, the
judgment of good music in particular would be crucial in any courtship display, and it is expected to be particularly so when women are at their most fertile. Female performance in music dichotic listening tasks has been shown to be dependent on position in the menstrual cycle. A switch from left hemisphere music interpretation to use of the right hemisphere
appears to be favored when estrogen levels are low (Sanders and Wenmoth, 1998). It is possible that ovulation, which is associated with low estrogen concentrations, is correlated with
enhanced musical appreciation.
If males are using music in courtship, what is it signaling? The answer may be prenatal exposure to testosterone. Geschwind and Galaburda (1985) suggested that fetal testosterone
may compromise the development of the left hemisphere, resulting in impaired fluency and
other aspects of language and a tendency toward left-handedness. They also speculate that
development of the right hemisphere is facilitated, leading to enhanced musical, spatial, and
mathematical abilities. It is difficult to test this hypothesis directly, because in utero testosterone levels are not readily determined. Indirect tests of the overall hypothesis have led to
mixed and often negative results (Bryden et al., 1994; Gilger et al., 1992, 1998). However,
there is some confirmation of the association between music and right hemisphere function.
In a study of the cerebral hemodynamics of music perception, Evers et al. (1999) reported
right hemisphere lateralization for harmony perception and a delay in the lateralization in
nonmusicians compared to musicians. They concluded that nonmusicians and musicians
have different lateralization strategies with regard to harmony perception. The former have a
marked right hemisphere lateralization, whereas the latter also may use their left hemisphere.
Brain damage and cortectomy provide an opportunity to study the effect of lesions on the
perception of music. Many of these studies confirmed the importance of the right hemisphere
in the perception of pitch presented in isolation, in chords, or in melodies (Peretz, 1990) and
the use of contour and interval information in the discrimination of melodies (LiegeoisChauvel, 1998).
It is not possible to directly test prenatal testosterone levels of accomplished musicians.
However, the ratio between the length of the second digit (2D) and fourth digit (4D) may
provide an indirect test of the association. The 2D:4D ratio is sexually dimorphic, with male
2D:4D lower on average than female (Baker, 1888; George, 1930; Phelps, 1952). Manning et
al. (1998) measured 2D:4D ratio and hormonal levels in a sample of 60 men and 40 women
attending an infertility clinic. They reported negative associations between 2D:4D ratio and
sperm number (r ⫽ ⫺.37, p ⫽ .004) and testosterone (r ⫽ ⫺.29, p ⫽ .03, men only) and positive relationships between estrogen and 2D:4D (r ⫽ .33, p ⫽ .002, men and women). The
waist to hip ratio (a proxy for testosterone concentrations) in a sample of Jamaican women
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also has been shown to be negatively correlated with 2D:4D in their children (Manning et al.,
1999). That is, women with high levels of serum testosterone have children with low 2D:4D
ratios. The 2D:4D ratio is independent of age (Manning et al., 1998), and evidence from fetal
material suggests that it is fixed by week 14 of development (Garn et al., 1975). The formation of the testes and the digits is influenced by Homeobox (Hox) genes found in the Hoxa
and Hoxd groups (Herault et al., 1997; Peichel et al., 1997). The fetal testes produce large
amounts of testosterone from about week 8 of development (Tanner, 1990). Therefore, perturbations in the formation of the testes may be linked directly to patterns of digit formation.
Alternatively, testosterone may stimulate growth of the fourth digit. If this is so, perturbations in testicular function may be reflected in fetal testosterone production and, therefore, in
patterns of digit growth. We presently are investigating the distribution of testosterone receptors on fetal digits. It remains possible that associations between 2D:4D, testosterone, and estrogen reflect in utero hormonal levels. Reproductive success depends on more than sperm
production and concentrations of testosterone and estrogen. However, Manning et al. (1999)
found evidence for a negative relationship between male 2D:4D and offspring number in
samples from England and Spain, and a positive relationship between female 2D:4D ratio
and family size in samples from England, Germany, and Hungary. It may be that behavioral
traits (e.g., musical and spatial ability) associated with high prenatal testosterone and low estrogen concentrations could be used by females to judge male fertilizing ability.
The purpose of this work was (a) to compare the 2D:4D ratio in elite musicians (members
of a British symphony orchestra) with that of controls and (b) to examine the relationship between 2D:4D ratio and musical ability within the orchestra.
1. Methods
Our subjects were 70 symphony musicians (54 men and 16 women) who were recruited
from a British symphony orchestra (the Orchestra requested anonymity). The male sample
consisted of the following instrument groups: violin (15 subjects), viola (6), cello (6), horn
(6), bass (5), trombone (3), percussion (3), bassoon (3), clarinet (2), oboe (1), flute (1), trumpet (1), tuba (1), and timpani (1). The female sample included violin (5 subjects), viola (5),
cello (2), harp (1), piccolo (1), oboe (1), and flute (1).
Controls (86 men and 78 women) were recruited from adult social clubs and part-time
adult classes of the University of Liverpool. Recruitment was restricted to an age range of 20
to 60 years. The catchment area for this sample included inner city, suburban, and rural areas.
The age of the participants was recorded and the length of the left and right second and
fourth digits measured on the palmar surface of the hand from the proximal crease to the tip
of the digit. It is known that this measurement can be made with high repeatability (Manning,
1995; Manning et al., 1998). All measurements were made with vernier calipers measuring
to 0.01 mm. Thirty hands from 30 subjects were measured twice to establish the repeatability
of our 2D:4D ratios.
To determine the sex composition and distribution of the concert audience, we counted the
number of women and men in the first four rows of the centre stalls and in the four back
rows. This was done at 11 concerts given by our subject orchestra.
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2. Results
Repeatabilities were high for the 2D:4D ratio (r1 ⫽ .99), and the ratio of within-subject
measurement error to between-subject differences in 2D:4D was significant (model II analysis of variance, F ⫽ 270.43, p ⫽ .0001) (Zar, 1984). We concluded that our 2D:4D ratios
represented real differences between our subjects.
Mean ages of our musician and control samples were similar (males, musicians x ⫽ 41.61 ⫾
10.19 [SD] years and controls x ⫽ 41.83 ⫾ 8.27, t ⫽ 0.14, p ⫽ .89; females, musicians x ⫽
33.00 ⫾ 6.96 years and controls x ⫽ 34.56 ⫾ 7.75 years, t ⫽ 0.75, p ⫽ .46).
Male musicians had mean 2D:4D ratios as follows: left hand x ⫽ 0.96 ⫾ 0.03 SD and
right hand x ⫽ 0.93 ⫾ 0.03. Male controls had higher 2D:4D ratios: left hand x ⫽ 0.98 ⫾
0.03 and right hand x ⫽ 0.98 ⫾ 0.04. The difference between mean 2D:4D ratios of musicians and controls was highly significant (left hand, t ⫽ 4.32, p ⫽ .0001; right hand, t ⫽
7.34, p ⫽ .0001; Fig. 1). The mean 2D:4D ratios found in the controls were very similar (x ⫽
0.98) to mean ratios reported for a sample of 400 males from the Merseyside population (our
present controls were not drawn from this sample). Manning et al. (1999) found significant
differences between mean 2D:4D ratios sampled from different countries. The musicians included two Scandinavian men. The difference between mean 2D:4D of the musicians and
controls remained significant after removal of the Scandinavian subjects (musicians left hand
x ⫽ 0.96 ⫾ 0.03 and controls x ⫽ 0.98 ⫾ 0.03, t ⫽ 4.04, p ⫽ .0001; musicians right hand x ⫽
0.94 ⫾ 0.03 and controls x ⫽ 0.98 ⫾ 0.04, t ⫽ 7.03, p ⫽ .0001).
Female musicians had mean 2D:4D ratios as follows: left hand x ⫽ 1.00 ⫾ 0.04 and right
hand x ⫽ 0.98 ⫾ 0.05. Female controls had similar mean ratios that did not differ significantly from the musicians (controls left hand x ⫽ 1.00 ⫾ 0.04, t ⫽ 0.56, p ⫽ .58; right hand
x ⫽ 0.99 ⫾ 0.04, t ⫽ 1.38, p ⫽ .17). An earlier sample of Merseyside females (n ⫽ 400)
gave similar mean female 2D:4D ratios (x ⫽ 1.00) (Manning et al., 1998). There were highly
significant differences between the mean 2D:4D ratios of male and female musicians in our
orchestra sample (left hand t ⫽ 5.09, p ⫽ .0001; right hand, t ⫽ 4.58, p ⫽ .0001). This suggested that these samples should not be pooled.
There was no evidence of significant differences in 2D:4D between male musicians who
played different instruments. For example, dividing the male sample into string and nonstring
instrument players gave similar mean 2D:4D ratios (left hand: strings n ⫽ 31, x ⫽ 0.96 ⫾
0.03, nonstrings n ⫽ 23, x ⫽ 0.96 ⫾ 0.03, t ⫽ 0.45, p ⫽ .65; right hand: strings n ⫽ 31, x ⫽
0.93 ⫾ 0.03, nonstrings n ⫽ 23, x ⫽ 0.94 ⫾ 0.03, t ⫽ 0.57, p ⫽ .57). This suggests that the
low 2D:4D ratios seen in the male musicians do not reflect mechanical advantages in actually
playing instruments. If this were so, differences in 2D:4D would emerge between musicians
playing different instruments. A similar division into string and nonstring instruments gave
similar nonsignificant results among women musicians (left hand: string x ⫽ 1.00 ⫾ 0.03, nonstring x ⫽ 1.00 ⫾ 0.03, t ⫽ 0.19, p ⫽ .85; right hand: string x ⫽ 0.97 ⫾ 0.04, nonstring x ⫽
1.00 ⫾ 0.07, t ⫽ 0.80, p ⫽ .44).
Symphony orchestras are hierarchical in that, within each section or instrument group,
there are positions allocated that represent a judgment of relative individual ability. Some
sections may contain one musician (e.g., timpani), whereas in others we had measurements
on one subject only. In the male sample, we had 39 ranked individuals in sections with two
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Fig. 1. Distribution of 2D:4D ratio in the right hand of 54 male symphony orchestra musicans and 86 male controls.
or more musicians. The largest group was that of the male violinists, 14 of whom had a section position. A regression of section position on 2D:4D showed a significant positive (low
position ⫽ high rank) relationship for the left hand, i.e., male violinists with low 2D:4D ratio
in the left hand were highly placed in the section (left hand b ⫽ 208.61, F ⫽ 7.10, p ⫽ .02;
right hand b ⫽ 68.67, F ⫽ 1.45, p ⫽ .25; Bonferroni correction for two tests p ⫽ .04 for left
hand) (Fig. 2). Considering the sections with two or more ranked members, we divided each
section into two groups. One contained the top ranked musician down to the middle ranked;
the other contained the lower ranked musicians. In all there were 20 participants in the former
and 19 in the latter group. The high ranking group had a significantly lower left hand 2D:4D
ratio compared to the low ranking group (left hand: high ranking group x ⫽ 0.95 ⫾ 0.03, low
ranking group x ⫽ 0.97 ⫾ 0.02, t ⫽ 3.15, p ⫽ .003; right hand: high ranking group x ⫽ 0.92
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Fig. 2. Position in the violin section regressed on 2D:4D ratio of the left and right hand of 14 male violinists (low
section position ⫽ high rank).
⫾ 0.03, low ranking group x ⫽ 0.94 ⫾ 0.02, t ⫽ 1.46, p ⫽ .15; Bonferroni correction for two
tests left hand p ⫽ .006). These results lead us to believe that judgments of relative ability
within the male members of the orchestra were correlated with 2D:4D in that low ratio is associated with high ability. Our female sample of 16 musicians distributed among seven sections was too small to relate 2D:4D ratio to section position.
We found evidence of a nonrandom distribution of women and men in the center stalls.
The rows nearest the orchestra contained a higher proportion of women than the rows at the
back of the stalls. We counted 1,750 members of the audience in 11 concerts. In the first four
rows of the center stalls there was a total of 820 individuals made up of 565 women (69% ⫾
5.90% SD) and 255 men (31%). In the last four rows there were 930 individuals made up of
477 women (51% ⫾ 6.35%) and 453 men (49%). This distribution of women and men was
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nonrandom (␹2 ⫽ 56.47, p ⫽ .0001). The percentage of women in the front stalls varied from
63 to 78 and in the back stalls from 41 to 59. In all concerts there was a higher percentage of
women in the front stalls compared to the back.
3. Discussion
Our sample of elite male musicians had lower 2D:4D ratios than the population norms.
There was evidence of significant relationships between 2D:4D ratio and ranking of male
musicians within the orchestra. Low 2D:4D was associated with high rank. We found no evidence that 2D:4D was related to mechanical advantage in the playing of particular instruments. Furthermore, female representation in seats close to the orchestra was greater than expected by chance.
Our results are consistent with an evolutionary origin of music through sexual selection.
So what does male musical ability signal to women? A trait used by males in courtship may
signal a direct benefit to females, e.g., fertility or parental care (Price et al., 1993), or it may
signal a benefit to the female’s offspring because it is correlated in some way with “good
genes” in the male (Kokko and Lindstrom, 1996; Manning, 1985; Zahavi, 1977). Of course,
these possibilities are not mutually exclusive. For example, fertilizing ability may depend on
good genes. The problems that arise with models of mate choice include the maintenance of
honesty in signaling (i.e., how is the spread of cheating genes opposed) and, in the case of
good genes models, how the additive genetic variance for the trait is maintained. Male musical ability may provide an honest signal of male fitness because it signals prenatal testosterone exposure, which itself is correlated with the efficient formation of the testes. In addition,
it may indicate to females that their sons will benefit from the genes for fertilizing ability advertised by their father. Genes of this nature often are advantageous in one sex but not the
other (sexually antagonistic genes) (Rice and Holland, 1997). Additive variance associated
with sexually antagonistic genes is maintained by selection because they find themselves in
both male and female bodies. A major disadvantage to a good gene model, i.e., loss of additive variance, is avoided if the genes preferred by females are sexually antagonistic.
With regard to the evolution of male musical ability, this study needs to be extended to
other symphony orchestras and to musicians in other forms of music. In particular, our results do not exclude the possibility that low 2D:4D correlates with membership and position
in the orchestra because it is associated with testosterone-mediated competitive behavior.
More work is needed to relate 2D:4D to musical ability per se. However, on the basis of our
preliminary data, we suggest the following model. A fetus is exposed to testosterone derived
from its own testes and from the maternal bloodstream (George et al., 1981; Tanner, 1990). It
also is exposed to estrogen produced by the placenta and derived from the mother (Trichopoulos, 1990). Testosterone probably is beneficial to a male fetus because it is necessary
for differentiation of the testes and for later spermatogenesis. Estrogen is important in the
formation of the female urinogenital system and the breast buds (Imagawa et al., 1994).
Genes for prenatal testosterone and estrogen production are sexually antagonistic. Therefore,
sex-limited expression has evolved so that testosterone production is enhanced and estrogen
reduced when the fetus is male and vice versa when it is female. However, a sex-limited phe-
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notype is difficult to evolve (Rice, 1996) so that its expression is incomplete. This means that
in many males prenatal exposure to estrogen is too high and in many females exposure to testosterone is too high. Testosterone enhances the growth of the right hemisphere and may facilitate musical ability. If it does so, musical ability then is a signal for male fertilizing ability, i.e., a direct benefit to the choosy female. Of course, males may have high prenatal
testosterone and not develop good musical ability. Such males may advertise their fertility in
other ways, e.g., enhanced spatial ability would be advantageous in male to male aggression
or in sports such as soccer. Nevertheless, musical ability, when present, is likely to be associated with male fertility. How then is the honesty of the signal maintained? Honesty in signals
may be maintained if there is a condition-dependent cost to the signal. Geschwind and Galaburda (1985) suggest that high levels of prenatal testosterone are also associated with autism,
dyslexia, migraine, stammering and a compromised immune system. Manning et al. (1999)
found that autistic children and their parents have lower 2D:4D ratios than population norms.
In addition, male adult depression symptoms have been reported as being correlated with
fourth digit length corrected for height of the subject (Martin et al., 1999). Exposure to high
concentrations of prenatal testosterone may have deleterious results if fetal phenotypic quality is low (Manning and Bundred, in press). Phenotypic quality itself may be partly determined by good genes. If so, musical ability in a male who is not compromised by depression,
autism, etc., could signal male fertilizing ability, sexually antagonistic genes that are advantageous in male children, and overall good genes. These are benefits that are likely to interest
females and therefore may explain the elaboration of human music by sexual selection.
Acknowledgment
Our thanks to the orchestra for permission to measure and to our subjects, musicians, and
nonmusicians who showed great patience in allowing us to measure their digits.
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