Original articleMating context and menstrual phase affect women's preferences for male voice pitch
Introduction
Voice pitch is the most salient acoustic feature of human speech (Banse & Scherer, 1996). Voice pitch is also sexually dimorphic; males speak up to an octave lower than females do, on average (e.g., Klatt & Klatt, 1990). This sexual dimorphism is not due merely to sex differences in body size. Relative to both height and body volume, vocal fundamental frequency (F0, the acoustic parameter most closely related to pitch) is lower in adult males than in adult females and prepubescent children of both sexes (Titze, 2000).
The proximate and developmental causes of this male secondary sex characteristic are known. Adult males have 60% longer membranous portions of the vocal folds, which vibrate at a lower F0. Vocal anatomy is masculinized under the influence of pubertal androgens, which cause males' vocal folds to increase in size faster than the overall rate of body growth (Hollien, 1960). Moreover, circulating androgens appear to maintain masculine vocal fold morphology in adults; F0 correlates negatively with androgen levels in men (Dabbs & Mallinger, 1999) and decreases with androgen treatment (Need, Durbridge, & Nordin, 1993).
By contrast, little is known about why men evolved this developmental pattern. Some evidence suggests that low F0 increased males' attractiveness to females. Oguchi and Kikuchi (1997) found that male voices rated as highly attractive by Japanese university students were significantly lower in voice pitch (VP) than were the voices rated as less attractive. Additionally, Collins (2000) found that Dutch women rated lower male voices as being significantly more attractive. However, because of their correlational designs, these studies could not demonstrate that pitch (P), in itself, affects vocal attractiveness.
Nonetheless, if female choice shaped male VP over human evolution, this preference requires explanation. Mate preferences are costly and generally evolve because they provide compensatory benefits (Andersson, 1994). In many species, female preferences apparently function in recruiting mates of high genetic quality, and androgen-dependent traits are often the foci of such preferences (Andersson, 1994). The degree of expression of androgen-dependent traits may signal fitness because androgens are immunosuppressant (Grossman, 1985) and can be produced at high levels only by otherwise healthy individuals (Folstad & Karter, 1992; see also Zahavi & Zahavi, 1997). Evidence from nonhuman animals (reviewed in Andersson, 1994) and humans (e.g., Gangestad & Thornhill, 2003, Scheib et al., 2003) suggests that some masculine traits are reliable fitness indicators, and genetic transmission of these fitness benefits has been demonstrated in some species (e.g., Norris, 1993, Reynolds & Gross, 1992).
In humans, female preferences for androgen-dependent (masculine) features show signs of complex design (Williams, 1966) for recruiting good genes. For example, women's mate preferences vary with probability of conception, such that women in the follicular (fertile) phase of their menstrual cycles exhibit preference shifts toward more masculine facial features (Johnston et al., 2001, Penton-Voak et al., 1999, Penton-Voak & Perrett, 2000) and odors (Grammer, 1993). Moreover, women's preferences for androgen-dependent features may be greater when evaluating men as short-term sex partners rather than as long-term mates (Penton-Voak et al., 1999; reviewed in Penton-Voak & Perrett, 2001). Because low VP is androgen dependent, it may also signal heritable fitness, and women's preferences for low VP may similarly depend on mating context and menstrual phase. Indeed, some studies have found that women prefer the voices of men who carry other fitness markers, such as external body symmetry and a high shoulder-to-hip ratio (Hughes et al., 2004, Hughes et al., 2002).
The present study thus evaluates the predictions of one hypothesis for the evolution of low voice pitch in human males: Women prefer males with low voices because VP reflected heritable fitness in ancestral environments. Specifically, I test whether low male VP (1) increases short-term, sexual attractiveness more than long-term relationship attractiveness, (2) is more attractive to women nearer peak fertility, and (3) predicts higher mating success. Unlike previous studies (Collins, 2000, Oguchi & Kikuchi, 1997), this study uses an experimental, rather than correlational, design by examining the effects of computer-based pitch manipulations on attractiveness ratings.
Section snippets
Participants
One hundred eleven male and 142 female self-identified heterosexual undergraduate students from the University of Pittsburgh participated. The mean age of the males was 18.9 years (range=18–24, S.D.=1.2), and the mean age of the females was 19.1 years (range=18–30, S.D.=1.7). Male participants were native English-speaking nonsmokers who reported not being involved in committed relationships. Female participants reported not taking hormonal contraception and having regular menstrual cycles.
Male participants: VP in competition for mates
To
Results
An initial regression analysis revealed a moderate but significant linear relationship—and, in each case, a less significant quadratic relationship—between unmanipulated VP and each of the four categories of attractiveness ratings (short-term/fertile, short-term/nonfertile, long-term/fertile, and long-term/nonfertile). Linear relationships between F0 (predictor variable) and attractiveness ratings ranged from p=.003, β=−.27, and r2=.07 for short-term/fertile to p=.036, β=−.17, and r2=.03 for
Discussion
Women prefer the utterances of men who speak at a low pitch. This conclusion is supported by previous studies (Collins, 2000, Oguchi & Kikuchi, 1997) as well as by the present study, in which significant negative linear relationships were observed between the F0 of spontaneous male utterances and women's ratings of those utterances. However, these correlations do not appear to be driven by an effect of VP itself on attractiveness ratings. In the present study, variations among utterances, such
Acknowledgments
I thank Steve Gaulin for many helpful comments on previous drafts; Katherine Verdolini for methodological and logistic support; Steve Gangestad for advice regarding menstrual cycle data collection; Lisa Brevard, Rachel Chandler, Christina Jerzyk, Jerome Lee, Rebecca Prosser, John Putz, Melinda Putz, and Linda Snyder for their generous assistance during various phases of experiment preparation and data collection; and Martin Daly, Vera Kempe, Margo Wilson, and two anonymous reviewers for their
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Note. A previous version of this paper received the 2004 New Young Investigator award from the Human Behavior and Evolution Society.
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Current address: Neuroscience Program, 108 Giltner Hall, Michigan State University, East Lansing, MI 48824, USA.