physical size and voice pitch: biology of physical versus social advantage

silverback gorilla

Among non-human primates, females compete physically and aggressively.  For example, pairs of female chimpanzees have been observed snatching and eating other females’ infants.[1]  Females killing other females’ infants, while discussed much less than male infanticide in the scholarly literature, has been observed in over 50 species.[2]  Females also engage in group physical aggression:

In social primates, aggressive exchanges often involve kin of the principal protagonists. In vervet monkeys, adult females who have been displaced from food sources may seek out and attack their displacer’s relatives. In macaques, members of different matrilineal groups ally with each other and individuals that have been displaced or attacked by members of another matriline commonly respond by attacking a vulnerable member of the aggressor’s matriline. [3]

The general understanding that females are less physically aggressive than males is true for humans.[4]  But that’s not true for all female animals.

Human adult males on average are larger than human adult females.  Across twenty-two small-scale societies for which data are available, a man is typically 7.4 kg heavier and 10.7 cm taller than a woman.[5]  That means in a direct physical confrontation, all else equal, a man is likely to have an advantage over a woman.  Humans are highly social, highly communicative animals.  Communication is valuable for organizing and coordinating coalitions and prevailing in conflicts.[6]  In conflicts between multi-party antagonists, women’s communicative superiority to men becomes more important.

Men’s larger physical size relative to women has a communicative cost.  A larger vocal organ makes a lower frequency sound.  Across animal species, lower frequency sounds are associated with competition for dominance and hostile interactions.  Higher frequency sounds cause less distress and are more associated with affiliative behavior.[7]  Men on average have much lower pitch voices than women do.[8]  This sex dimorphism in vocal pitch implies that, all else equal, both women and men prefer supportive communication with women.  In societies in which persons predominately value and remember how persons made them feel, women’s higher average voice pitch is a biological advantage.

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Notes:

[1] Pusey, Williams & Goodall (1997).  High-status female chimpanzees have significantly greater reproductive success than low-ranking female chimpanzees.

[2] Digby (2000) p. 429.

[3] Clutton-Brock & Parker (1995) p. 211.

[4] Archer (2004) pp. 302-5.

[5] Calculated using data in Walker et al. (2006), Tables 2 and 3.  Given values calculated based on the median of sex ratios, evaluated at median male figures (weight 55.6 kg, height 158.5 cm). As id., p. 305, notes, male growth rates are less plastic across societies.

[6] Owings & Morton (1998), pp. 101-4, discusses vocal communication as a substitute for fighting with large muscle movements.

[7] Id. pp. 105-25.  Puts, Gaulin & Verdolini (2006).

[8] An average value for the fundamental frequency of human speech is 120 Hz for men and 210 Hz for women. At the fundamental frequencies, this difference amounts to about 10 semitones. The standard deviation for male and female fundamental voice frequencies is about 3 semitones. Traunmüller (1995) p. 1.  In ordinary life, adult voice pitch is a good sex determinant.

References:

Archer, John. 2004. “Sex Differences in Aggression in Real-World Settings: A Meta-Analytic Review.” Review of General Psychology 8(4): 291-322.

Clutton-Brock, T. H. and G. A. Parker. 1995. “Punishment in animal societies.” Nature 373: 209-216.

Digby, Leslie. 2000. “Infanticide by female mammals: implications for the evolution of social systems.” Pp. 423-65 in Carel P. Van Schaik and Charles H. Janson, eds. Infanticide by males and its implications. Cambridge: Cambridge University Press.

Owings, Donald H. and Eugene S. Morton. 1998. Animal vocal communication: a new approach. Cambridge: Cambridge University Press.

Pusey, Anne, Jennifer Williams and Jane Goodall. 1997. “The Influence of Dominance Rank on the Reproductive Success of Female Chimpanzees.” Science 277(5327): 828-831.

Puts, Andrew David, Steven J.C. Gaulin and Katherine Verdolini. 2006. “Dominance and the evolution of sexual dimorphism in human voice pitch.” Evolution and Human Behavior 27: 283-296.

Traunmüller, Hartmut and Anders Eriksson. 1995. “The frequency range of the voice fundamental in the speech of male and female adults.”

Walker, Robert, Michael Gurven, Kim Hill, Andrea Migliano, Napoleon Chagnon, Roberta De Souza, Gradimir Djurovic, Raymond Hames, A. Magdalen Hurtado, Richard Kaplan, Karen Kramer, William J. Oliver, Claudia Valeggia and Taro Yamauchi. 2006. “Growth Rates and Life Histories in Twenty-Two Small-Scale Societies.” American Journal of Human Biology 18: 295-311.

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