Group size and mating system predict sex differences in vocal fundamental frequency in anthropoid primates

Abstract

Vocalizations differ substantially between the sexes in many primates, and low-frequency male vocalizations may be favored by sexual selection because they intimidate rivals and/or attract mates. Sexual dimorphism in fundamental frequency may be more pronounced in species with more intense male mating competition and in those with large group size, where social knowledge is limited and efficient judgment of potential mates and competitors is crucial. These non-mutually exclusive explanations have not been tested simultaneously across primate species. In a sample of vocalizations (n = 1914 recordings) across 37 anthropoid species, we investigated whether fundamental frequency dimorphism evolved in association with increased intensity of mating competition (H1), large group size (H2), multilevel social organization (H3), a trade-off against the intensity of sperm competition (H4), and/or poor acoustic habitats (H5), controlling for phylogeny and body size dimorphism. We show that fundamental frequency dimorphism increased in evolutionary transitions towards larger group size and polygyny. Findings suggest that low-frequency male vocalizations in primates may have been driven by selection to win mating opportunities by avoiding costly fights and may be more important in larger groups, where limited social knowledge affords advantages to rapid assessment of status and threat potential via conspicuous secondary sexual characteristics.

Effects of Voice Pitch on Social Perceptions Vary With Relational Mobility and Homicide Rate

“…Across cultures, men were likewise more likely to display beards, another putative status badge, rather than shaving under crowded conditions with high anonymity (Dixson et al, 2017). Moreover, cross-species analyses indicate that conspicuous visual (Grueter et al, 2015) and acoustic (Aung, Hill, et al, 2023) female mate choice in shaping this preference because females may prefer high-status males especially in longterm contexts (Buss & Schmitt, 1993). However, our results are inconsistent with the hypotheses that women's masculinity preferences are stronger in short-term mating contexts to recruit heritable fitness benefits for offspring (e.g., Puts, 2005) or in violent environments because of an increased need for protection (Brooks et al, 2011).…”

“…Assessing rivals through conspicuous, sexually differentiated traits may also be more important in large, complex social environments in which social knowledge is limited. Comparative research suggests that visually conspicuous male status badges (Grueter et al, 2015) and relatively lower male f o (Aung, Hill, et al, 2023) evolve in anthropoid primate species with larger group sizes. In humans, conspicuous status signals may be particularly salient in societies characterized by higher relational mobility, a socioecological measure that represents freedom and opportunity to form interpersonal relationships based on personal preferences (Thomson et al, 2018).…”

Globally, men and women’s singing and speaking voices are not exactly one octave apart: Commentary on Bannan et al., “The evolution of gender dimorphism in the human voice: The role of octave equivalence”

“…This all suggests that the sexual dimorphism in human vocal production does not quite align precisely with the octave. This does not necessarily undercut Bannan et al's argument -the dimorphism is indeed almost an octave, and this is much greater than for other apes (Aung et al 2023). Since human vocal pitch production is quite flexible, it is clearly close enough to an octave to enable men and women/children around the world to sing in octave harmony (Savage et al 2015;Mehr et al 2019;Brown and Jordania 2013), which is indeed generally perceived as unison via the phenomenon of octave equivalence.…”

“…All data in Table 1 and Figure 2 is taken from the publicly available sources in the relevant publications (Aung et al, 2023;Hilton et al, 2022;Ozaki et al, 2022;Puts et al, 2012Puts et al, , 2016.…”

Human Male Body Size Predicts Increased Knockout Power, Which Is Accurately Tracked by Conspecific Judgments of Male Dominance

“…age on opponents (Emlen, 2008;McCullough et al, 2016) whereas ornamental features communicate social rank and dominance without necessarily being related to physical formidability (Dixson et al, 2005;Grueter et al, 2015; for more crossprimate evidence of ornamental features, see Aung et al, 2023; but also see Aung et al, 2020;Aung & Puts, 2020;Puts & Aung, 2019;Rendall et al, 2007). However, both improve male resource-holding power (Arnott & Elwood, 2009).…”