ANIMAL BEHAVIOUR, 2000, 60, 773–780 doi:10.1006/anbe.2000.1523, available online at http://www.idealibrary.com on Men’s voices and women’s choices SARAH A. COLLINS Behavioural Biology Section, Institute of Evolutionary & Ecological Sciences, Leiden, The Netherlands (Received 21 March 2000; initial acceptance 10 May 2000; final acceptance 5 July 2000; MS. number: 6530) I investigated the relationship between male human vocal characteristics and female judgements about the speaker. Thirty-four males were recorded uttering five vowels and measures were taken, from power spectrums, of the first five harmonic frequencies, overall peak frequency and formant frequencies (emphasized, resonance, frequencies within the vowel). Male body measures were also taken (age, weight, height, and hip and shoulder width) and the men were asked whether they had chest hair. The recordings were then played to female judges, who were asked to rate the males’ attractiveness, age, weight and height, and to estimate the muscularity of the speaker and whether he had a hairy chest. Men with voices in which there were closely spaced, low-frequency harmonics were judged as being more attractive, older and heavier, more likely to have a hairy chest and of a more muscular body type. There was no relationship between any vocal and body characteristic. The judges’ estimates were incorrect except for weight. They showed extremely strong agreement on all judgements. The results imply that there could be sexual selection through female choice for male vocal characteristics, deeper voices being preferred. However, the function of the preference is unclear given that the estimates were generally incorrect.  2000 The Association for the Study of Animal Behaviour Relationships between acoustic parameters and body size (Appleby & Redpath 1997; Giacoma et al. 1997), hormonal status (Fusani et al. 1994; Beani et al. 1995) and age (Ballintijn & ten Cate 1997) have been found in a number of taxa (birds, anurans and some mammals). However, the relationships between acoustic parameters and individual characteristics in primates (including humans) appear to be more complex (Lass & Brown 1978; van Dommelen 1993; Hauser 1993). One commonly found relationship, in nonprimate species, is between the acoustic frequency of a vocaliz- ation and body size: larger individuals produce lower- frequency sounds (Morton 1977; Howard & Young 1998). The relationship between body size and frequency holds across primate species (Hauser 1993), but not within species (Fitch 1997). Most people believe that a deep human voice (i.e. a low-frequency voice) indicates a larger person, although this is not true (van Dommelen & Moxness 1995). As pointed out by Fitch (1997), this is not surprising when one considers the structure of the vocal apparatus in primates. The fundamental frequency of the voice, in both nonhuman primates and humans, is dependent upon the thickness and size of the vocal folds (Fant 1960; Lieberman 1984; Scho ¨n Ybarra 1995) which are soft tissues. Testosterone increases the size and thickness of the folds (Hollien 1960; Beckford et al. 1985). Changes in the vocal apparatus occur at the same time as changes in body shape and size during puberty, but the relative increase in the size of the vocal folds is greater than that in body size (Hollien et al. 1994) and is independent of measures of skeletal size (Beckford et al. 1985). During adolescence, there is a correlation between vocal frequency and body size, because body size increases and the voice deepens simultaneously, although the correlation disappears during the latter stages of puberty (Hollien et al. 1994). However, some information about body size is con- tained in the vocalizations of primates. The vocal tract is made up of hard tissue, its length being related to both skull and skeletal size (Fitch & Hauser 1995; Fitch 1997) and the size of the tract determines the resonance fre- quencies of calls (Fant 1960; Lieberman & Blumstein 1988; Moore 1992). The resonance frequencies, known as formant frequencies, are emphasized frequencies within vocalizations (Fig. 1). Fitch (1997) showed that in rhesus macaques, Macaca mulatta, the length of the vocal tract and the formant frequencies produced are both related to body size. The same is probably true in baboons (Owren et al. 1997). More precisely, it is the difference in fre- quency between successive formant frequencies (formant dispersion) that correlates with body size. Larger indi- viduals have smaller differences between the formant frequencies (Fitch 1997). This information could be used by other individuals to infer body size. Correspondence and present address: S. A. Collins, Behavioural Ecol- ogy Research Group, School of Life and Environmental Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, U.K. (email: Sarah.Collins@nottingham.ac.uk). 0003–3472/00/120773+08 $35.00/0  2000 The Association for the Study of Animal Behaviour 773