1 Rowe, N. & Myers, M. 2011. All the World's Primates. Charlestown RI: Primate Conservation Inc (www.alltheworldsprimates.org). 2 Grueter, C.C. et al. 2015. Are badges of status adaptive in large complex primate groups? Evol. Hum. Behav. 36: 398–406. 3 Smith, R.J. & Jungers, W.L. 1997. Body mass in comparative primatology. J. Hum. Evol. 32: 523–559. 4 Plavcan, J.M. & Ruff, C.B. 2008. Canine size, shape, and bending strength in primates and carnivores. Am. J. Anat. 136: 65–84. 5 Harcourt, A.H. et al. 1995. Sperm competition: mating system, not breeding season, affects testes size of primates. Funct. Ecol. 9: 468–476. 6 Campbell C.J. et al. 2011. Primates in Perspective (2nd ed.). Oxford: Oxford University Press. 7 "Dunham, A.E. & Rudolf, V.H.W. 2009. Evolution of sexual size-monomorphism; the influence of passive mate-guarding. J. Evol. Biol. 22: 1376–1386." 8 Cramer, J.D. et al. 2013. Variation in scrotal color among widely distributed vervet monkey populations (Chlorocebus aethiops pygerythrus and Chlorocebus aethiops sabaeus). Am. J. Primatol. 75: 752–762. 9 Dunn, J.C. et al. 2015. Evolutionary trade-off between vocal tract and testes dimensions in howler monkeys. Curr. Biol. 25: 2839–2844. 10 Kaleita, M. et al. 2011. Impact of intrasexual selection on sexual dimorphism and testes size in the Mexican howler monkeys Alouatta palliata and A. pigra. Am. J. Phys. Anthropol. 146: 179–187. 11 Kappeler, P.M. & Haymann, E.W. 1996. Nonconvergence in the evolution of primate life history and socio-ecology. Biol. J. Linn. Soc. 59: 297–326. 12 Dixson, A.F. & Anderson, M.J. 2004. Sexual behavior, reproductive physiology and sperm competition in male mammals. Physiol. Behav. 83: 361–371. 13 This study, based on the same methods as in ref. 2. 14 Leal, M.C. & Franηa, L.R. 2006. The seminiferous epithelium cycle length in the black tufted-ear marmoset (Callithrix penicillata) is similar to humans. Biol. Reprod. 74: 616–624. 15 Thorιn, S., Lindenfors, P. & Kappeler, P.M. 2006. Phylogenetic analyses of dimorphism in primates: evidence for stronger selection on canine size than on body size. Am. J. Phys. Anthropol. 130: 50–59. 16 Gingerich, P.D. et al. 1982. Allometric scaling in the dentition of primates and prediction of body weight from tooth size in fossils. Am. J. Phys. Anthropol. 58: 81–100. 17 Mate, C., Colell, M. & Escobar, M. 1995. Preliminary observations on the ecology of forest Cercopithecidae in the Lokofe-Ikomaloki Region (Ikela, Zaire). Folia Primatol. 64: 196–200. 18 Anderson, M.J. & Dixson, A.F. 2009. Sexual selection affects the sizes of the mammalian prostate gland and seminal vesicles. Curr. Zool. 55: 1–8. 19 Lindenfors, P. 2002. Sexually antagonistic selection on primate size. J. Evol. Biol. 15: 595–607. 20 Scott, J.E. 2010. Nonsocial Influences on Canine Size in Anthropoid Primates. PhD thesis, Arizona State University. 21 Kappeler, P.M. 1997. Intrasexual selection and testis size in strepsirhine primates. Behav. Ecol. 8: 10–19. 22 Dixson, A.F. 2012. Primate Sexuality: Comparative Studies of the Prosimians, Monkeys, Apes, and Humans. Oxford University Press, Oxford, UK. 23 Layton, R. & O'Hara, S. 2010. Human social evolution: a comparison of hunter-gatherer and chimpanzee social organisation. In: Social Brain, Distributed Mind (ed.: R. Dunba, C. Gamble & J. Gowlett). British Academy 158, pp. 85–115. 24 Lucas, P.W. et al. 1986. Sexual dimorphism of tooth size in anthropoids. Hum. Evol. 1: 23–39. 25 Morrow, E.H. & Fricke, C. 2004. Sexual selection and the risk of extinction in mammals. Proc. R. Soc. B 271: 2395–2401. 26 Gordon, A.D. 2006. Scaling of size and dimorphism in primates II: Macroevolution. Int. J. Primatol. 27: 63–105. 27 Harding, L.E. 2010. Trachypithecus cristatus (Primates: Cercopithecidae). Mamm. Species 42: 149–165. 28 Burton, G.J. 1981. The relationship between body and gonadal weights of the dusky leaf monkey (Presbytis obscura). Int. J. Primatol. 2: 351–368.