Manipulations of fundamental and formant frequencies influence the attractiveness of human male voices

In human voices, low fundamental frequency is thought to be a cue to masculinity and reproductive capability and large vocal tracts are associated with large body size of the speaker. Female preferences for males with low fundamental frequencies and large vocal tract lengths are potentially adaptive. Although sexually dimorphic characteristics of male voices have been studied, the impact of manipulations of secondary sexual characteristics on preferences for male voices has not. We manipulated fundamental frequencies and apparent vocal tract lengths of young adult male voices, both independently and simultaneously, and assessed their impact on female ratings of masculinity, size, age and attractiveness. Lowering the fundamental frequencies and/or increasing apparent vocal tract lengths of male voices increased females' ratings of the masculinity, size and age of the speaker. Peer group females preferred male voices with (1) lowered fundamental frequencies to those with raised fundamental frequencies, and (2) original frequencies to male voices with raised fundamental frequencies and decreased apparent vocal tract lengths (a combined manipulation to reflect acoustic characteristics of 16-year-old male voices). This suggests that male voices with acoustic characteristics that reflect full sexual maturity may be attractive. Although no general preference was observed for male voices with increased or decreased apparent vocal tract lengths, female preferences for male voices with increased apparent vocal tract lengths were positively related to females' own body size. This latter finding may indicate assortative preferences for acoustic cues to body size.