Theoretical background

The human voice plays a crucial role in contexts of sexual selection (e.g. Hodges-Simeon et al., Reference Hodges-Simeon, Gaulin and Puts2010; O'Connor et al., Reference O'Connor, Pisanski, Tigue, Fraccaro and Feinberg2014; Puts et al., Reference Puts, Hill, Bailey, Walker, Rendall, Wheatley and Ramos-Fernandez2016; Rosenfield et al., Reference Rosenfield, Sorokowska, Sorokowski and Puts2019), such as mate choice (Pisanski et al., Reference Pisanski, Oleszkiewicz, Plachetka, Gmiterek and Reby2018). Herein, especially one vocal characteristic, the fundamental frequency (mean F0), has repeatedly been linked to relevant perceptions and characteristics of speakers. F0 influences perceptions of voice pitch, such that lower F0 is associated with deeper pitch. Within sexes, F0 predicts various criteria across contexts and has been linked to, for example, reproductive success (e.g. Apicella et al., Reference Apicella, Feinberg and Marlowe2007; Rosenfield et al., Reference Rosenfield, Sorokowska, Sorokowski and Puts2019), hunting reputation (Smith et al., Reference Smith, Olkhov, Puts and Apicella2017) and corporate hierarchy (Mayew et al., Reference Mayew, Parsons and Venkatachalam2013). In male speakers, lower F0 is typically also related to being perceived as more attractive (e.g. Feinberg et al., Reference Feinberg, Jones, Little, Burt and Perrett2005; Jünger et al., Reference Jünger, Motta-Mena, Cardenas, Bailey, Rosenfield, Schild and Puts2018; Puts et al., Reference Puts, Hill, Bailey, Walker, Rendall, Wheatley and Ramos-Fernandez2016) and more dominant (e.g. Borkowska & Pawlowski, Reference Borkowska and Pawlowski2011; Hodges-Simeon et al., Reference Hodges-Simeon, Gaulin and Puts2010; Puts et al., Reference Puts, Hill, Bailey, Walker, Rendall, Wheatley and Ramos-Fernandez2016).

Meta-analytic evidence suggests that such perceptions are based on an honest signal of F0, as F0 provides valid information about the physical condition and formidability of speakers. For example, male individuals with lower F0 are taller (Pisanski et al., Reference Pisanski, Fraccaro, Tigue, O'Connor, Röder, Andrews and Feinberg2014) and stronger (Aung & Puts, Reference Aung and Puts2019) and have higher testosterone levels (Aung & Puts, Reference Aung and Puts2019). Importantly, however, these relations are relatively weak (r _height/F0 = −0.13, r _strength/F0 = −0.07 and r _{testosterone/F0} = −0.20; meta-analytic references above) and – for strength and testosterone – based on a relatively small number of studies (k _strength/F0 = 13, k _{testosterone/F0} = 8) with relatively small sample sizes (mean N _strength/F0 = 65.00, mean N _{testosterone/F0} = 95.38). Further, strength and height are rather indirect proxies for formidability, whereas evidence that links F0 to actual formidability of an individual is sparse. Although lower F0 predicted better hunting reputation in hunter–gatherers (Smith et al., Reference Smith, Olkhov, Puts and Apicella2017), studies focusing on intrasexual physical competition are hardly existing and/or contradictory. More precisely, given reduced direct male–male competition in contemporary societies, studies investigating whether traits – e.g. beardedness (Dixson et al., Reference Dixson, Sherlock, Cornwell and Kasumovic2018), facial morphometrics (Zilioli et al., Reference Zilioli, Sell, Stirrat, Jagore, Vickerman and Watson2015) and vocal characteristics (Šebesta et al., Reference Šebesta, Třebický, Fialová and Havlíček2019) – are linked to success in male–male competition have focused on sporting contests, ‘which remain active Darwinian arenas in which direct same-sex competition for status readily occur’ (Dixson et al., Reference Dixson, Sherlock, Cornwell and Kasumovic2018: 148). Herein, mixed martial arts (MMA) are typically considered as a good proxy of contest competition in ancestral human environments (e.g. Dixson et al., Reference Dixson, Sherlock, Cornwell and Kasumovic2018), as fights are limited by a few regulations only (e.g. strikes to genitals and eyes are forbidden). Importantly, the best MMA fighters typically receive very high rewards for competing, which suggests that success is indeed linked to higher societal status. Payouts for a single bout in the recent Ultimate Fighting Championship 249 event reached US$500,000 (DAZN, 2020).

While previous research suggests that (masculine) facial cues predict fighting success in male but not female MMA fighters (Little et al., Reference Little, Třebický, Havlíček, Roberts and Kleisner2015; Palmer-Hague et al., Reference Palmer-Hague, Zilioli, Jagore and DeLecce2016; Zilioli et al., Reference Zilioli, Sell, Stirrat, Jagore, Vickerman and Watson2015), mixed findings exist regarding links between F0 and fighting ability. F0 was not linked to fighting success, as indicated by the ratio between wins and losses, in a sample of amateur MMA fighters (Šebesta et al., Reference Šebesta, Třebický, Fialová and Havlíček2019). In contrast, F0 was negatively linked to the number of fights and the number of wins, but not to the percentage of wins, in a sample of professional MMA fighters in an unpublished master's thesis (Goetz, Reference Goetz2015). Importantly, Goetz (Reference Goetz2015) also found that the standard deviation of F0 (F0 SD), perceived as monotonicity, was linked to the number of fights and the number of wins, but not to the percentage of wins.

As recently argued by Aung and Puts (Reference Aung and Puts2019), further research is needed to investigate relations between F0 and formidability. To provide a well-powered test of a potential relation between F0 and formidability, we ran a study including data for 135 amateur MMA fights and 189 amateur boxing fights. This not only deepens our insights into how F0 is related to actual formidability, but also provides a rather direct test of the relation, given that dyadic fight data is available and it can be tested whether the difference in F0 between fighters can predict the outcome of a fight. We hypothesised that, on average, fighters with lower F0 are more likely to win their fights.