The penis is an incredibly diverse and rapidly evolving structure, such that even in closely related species that otherwise differ very little in their morphology, penis form can be highly differentiated. Penises are also much more complex than their fundamental function — sperm transfer — would seem to require. The rapid divergent evolution of male structures is typically the signature of traits under sexual selection and the current evidence suggests the penis is no different in this regard. Despite the general agreement that sexual selection is the main driver of penis evolution, many questions about penis evolution remain unresolved. Furthermore, the penis might be an ideal characteristic on which to focus in the drive to link phenotype with genotype.
Across animals with internal fertilization, the penis and associated structures evolve rapidly and divergently.
Penises are also much more complicated than their simple primary function, sperm transfer, would seem to require, and can sometimes even damage the female during copulation.
Sexual selection, and particularly female choice, is largely responsible for the diversity of the penis, although natural selection might occasionally act on penis form.
Despite rapid evolution, in most instances, selection on the penis does not seem to be particularly strong.
Evidence suggests the human penis is sexually selected, with increased penis size preferred by women in some studies, perhaps explaining why the human penis is large compared with most great apes.
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Eberhard, W. G. Sexual Selection and Animal Genitalia (Harvard Univ. Press, London, 1985).
Higgins, S., Hosken, D. J. & Wedell, N. Phenotypic and genetic variation in male genitalia in the seedbug, Lygaeus equestris (Heteroptera). Biol. J. Linn. Soc. 98, 400–405 (2009).
Kamimura, Y. & Matsuo, Y. A “spare” compensates for the risk of destruction of the elongated penis of earwigs (Insecta: Dermaptera). Naturwissenschaften 88, 468–471 (2001).
Yoshizawa, K., Ferreira, R. L., Kamimura, Y. & Leinhard, C. Female penis, male vagina, and their correlated evolution in a cave insect. Curr. Biol. 24, 1006–1010 (2014).
Rowe, L. & Arnqvist, G. Sexual selection and the evolution of genital shape and complexity in water striders. Evolution 66, 40–54 (2011).
Arnqvist, G. & Thornhill, R. Evolution of animal genitalia: patterns of phenotypic and genotypic variation and condition dependence of genital and non-genital morphology in waterstriders (Heteroptera: Gerridae: Insecta). Gen. Res. 71, 192–212 (1998).
Hosken, D. J. & Stockley, P. Sexual selection and genital evolution. Trends Ecol. Evol. 19, 87–93 (2004).
Simmons, L. W. Sexual selection and genital evolution. Austr. Entomol. 53, 1–17 (2014).
Andersson, M. Sexual Selection (Princeton Univ. Press, Princeton, 1994).
Pitra, C., Fickel, J., Meijaard, E. & Groves, P. C. Evolution and phylogeny of old world deer. Mol. Phyl. Evol. 33, 880–895 (2004).
Emlen, D. J., Marangelo, J., Ball, B. & Cunningham, C. W. Diversity in the weapons of sexual selection: horn evolution in the beetle genus Onthophagus (Coleoptera: Scarabaeidae). Evolution 59, 1060–1084 (2005).
Langerhans, R. B. in Ecology and Evolution of Poeciliid Fishes (eds Evans, J., Pilastro, A. & Schlupp, I.) 228–240 (Univ. of Chicago Press, Chicago, 2011).
Simmons, L. W. & Emlen, D. J. Evolutonary trade-off between weapons and testes. Proc. Natl Acad. Sci. USA 103, 16346–16351 (2006).
Heinen-Kay, J. L. & Langerhans, R. B. Predation-associated divergence of male genital morphology in a livebearing fish. J. Evol. Biol. 26, 2135–2146 (2013).
Hollander, J., Smadja, C. M., Butlin, R. K. & Reid, D. G. Genital divergence in sympatric sister snails. J. Evol. Biol. 26, 210–215 (2013).
Kameda, Y., Kawakita, A. & Kato, M. Reproductive character displacement in genital morphology in Satsuma land snails. Am. Nat. 173, 689–697 (2009).
Darwin, C. The Descent of Man and Selection in Relation to Sex (John Murry, London, 1871).
Hosken, D. J. & House, C. M. Sexual selection. Curr. Biol. 21, R62–R65 (2011).
Parker, G. A. in Sperm Competition and the Evolution of Animal Mating Systems (ed. Smith, R. L.) 1–60 (Academic Press, London, 1984).
Eberhard, W. G. Female Control: Sexual Selection by Cryptic Female Choice (Princeton Univ. Press, Princeton, 1996).
Pitnick, S. & Hosken, D. J. in Evolutionary Behavioural Ecology (eds Westneat, D. F. & Fox, C. W.) 379–399 (Oxford Univ. Press, Oxford, 2010).
Pizarri, T. & Birkhead, T. R. Female feral fowl eject sperm of subdominant males. Nature 405, 787–789 (2000).
Hodgson, D. J. & Hosken, D. J. Sperm competition promotes the exploitation of rival ejaculates. J. Theor. Biol. 243, 230–234 (2006).
Eberhard, W. G. Evidence for widespread courtship during copulation in 131 species of insects and spiders, and implications for cryptic female choice. Evolution 48, 711–733 (1994).
Edvardsson, M. & Arnqvist, G. Copulatory courtship and cryptic female choice in red flour beetles Tribolium castaneum. Proc. Biol. Sci. 267, 559–563 (2000).
Zervomanolakis, I. et al. Physiology of upward transport in the human female genital tract. Ann. NY Acad. Sci. 1101, 1–20 (2007).
Reeder, D. M. in Sexual Selection and Reproductive Competition in Primates: New Perspectives and Directions (ed. Jones, C. B.) 255–303 (American Society of Primotologists, Norman, 2003).
Leivers, S. & Simmons, L. W. Human sperm competition: playing a defensive strategy. Adv. Stud. Behav. 46, 1–44 (2014).
Hosken, D. J. Clitoral variation says nothing about female orgasm. Evol. Dev. 10, 393–395 (2008).
Dixson, A. F. Primate Sexuality (Oxford Univ. Press, Oxford, 1998).
Simmons, L. W., Firman, R. C., Rhodes, G. & Peters, M. Human sperm competition: testis size, sperm production and rates of extra-pair copulations. Anim. Behav. 68, 297–302 (2004).
Clark, A. G., Begun, D. J. & Prout, T. Female x male interactions in Drosophila sperm competition. Science 283, 217–220 (1999).
Evans, J. P., Zane, Francescato, L., S. & Pilastro, A. Directional postcopulatory sexual selection revealed by artificial insemination. Nature 421, 360–363 (2003).
Fairbairn, D. J. in Sex, Size & Gender: Evolutionary Studies of Sexual Size Dimorphism (eds Fairbairn, D. J., Blanckenhorn, W. U. & Szekely, T.) 97–105 (Oxford Univ. Press, Oxford, 2009).
House, C. M., Sharma, M. D., Okada, K. & Hosken, D. J. Pre and post-copulatory selection favor similar genital phenotypes in the male broad horned beetle. Integr. Comp. Biol. 56, 682–693 (2016).
Arnqvist, G. Comparative evidence for the evolution of genitalia by sexual selection. Nature 393, 784–786 (1998).
Ramm, S. A. Sexual selection and genital evolution in mammals: a phylogenetic analysis of baculum length. Am. Nat. 169, 360–369 (2007).
Simmons, L. W. Sperm Competition and it Evolutionary Consequences in the Insects (Princeton Univ. Press, Princeton, 2001).
Gage, M. J. G. Associations between body size, mating pattern, testis size and sperm length across butterflies. Proc. Biol. Sci. 258, 247–254 (1994).
Stockley, P., Gage, M. J. G., Parker, G. A. & Moller, A. P. Sperm competition in fishes: the evolution of testis size and ejaculate characteristics. Am. Nat. 149, 933–954 (1997).
Hosken, D. J. Sperm competition in bats. Proc. Biol. Sci. 264, 385–392 (1997).
Hosken, D. J. & Ward, P. I. Experimental evidence for testis size evolution via sperm competition. Ecol. Lett. 4, 10–13 (2001).
Brennan, P. L. R. et al. Coevolution of male and female genital morphology in waterfowl. PLOS ONE 5, e418 (2007).
Arnqvist, G. & Danielsson, I. Copulatory behaviour, genital morphology, and male fertilization success in water striders. Evolution 53, 147–156 (1999).
Córdoba-Aguilar, A. Male copulatory sensory stimulation induces female ejection of rival sperm in a damselfly. Proc. Biol. Sci. 266, 779–784 (1999).
House, C. M. & Simmons, L. W. Genital morphology and fertilisation success in the dung beetle Onthophagus taurus: an example of sexually selected male genitalia. Proc. Biol. Sci. 270, 447–455 (2003).
Xu, J. & Wang, Q. Form and nature of precopulatory sexual selection in both sexes of a moth. Naturwissenschaften 97, 617–625 (2010).
Stockley, P. et al. Baculum morphology predicts reproductive success of male house mice under sexual selection. BMC Biol. 11, 66 (2013).
Mautz, B. S., Wong, B. B. M., Peters, R. A. & Jennions, M. D. Penis size interacts with body shape and height to influence male attractiveness. Proc. Natl Acad. Sci. USA 110, 6925–6930 (2013).
Prause, N., Park, J., Leung, S. & Miller, G. Women’s preference for penis size: a new research method using selection among 3D models. PLOS ONE 10, e0133079 (2015).
Kahn, A. T., Mautz, B. & Jennions, M. D. Females prefer to associate with male with longer intromittent organs in mosquitofish. Biol. Lett. 6, 55–58 (2009).
House, C. M. & Simmons, L. W. The evolution of male genitalia: patterns of genetic variation and covariation in the genital sclerites of the dung beetle Onthophagus taurus. J. Evol. Biol. 18, 1281–1292 (2005).
Simmons, L. W., House, C. M., Hunt, J. & García-González, F. Evolutionary response to sexual selection in male genital morphology. Curr. Biol. 19, 1442–1446 (2009).
House, C. M. et al. Sexual and natural selection both influence male genital evolution. PLOS ONE 8, e63807 (2013).
Simmons, L. W. & Firman, R. C. Experimental evidence for the evolution of the mammalian baculum by sexual selection. Evolution 68, 276–283 (2014).
Preziosi, R. F. & Roff, D. A. Evidence of genetic isolation between sexually monomorphic and sexually dimorphic traits in the water strider Aquarius remigis. Heredity 8, 92–99 (1998).
House, C. M. & Simmons, L. W. No evidence for condition-dependent expression of male genitalia in the dung beetle Onthophagus taurus. J. Evol. Biol. 20, 1322–1332 (2007).
Hosken, D. J., Minder, A. M. & Ward, P. I. Male genital allometry in Scathophagidae (Diptera). Evol. Ecol. 19, 501–515 (2005).
Eberhard, W. G. et al. One size fits all? Relationships between the size and degree of variation in genitalia and other body parts in twenty species of insects and spiders. Evolution 52, 415–431 (1998).
Lessells, C. M. Why are males bad for females? Models for the evolution of damaging male mating behaviour. Am. Nat. 165, S46–S63 (2005).
Parker, G. A. Sexual conflict over mating and fertilization: an overview. Phil. Trans. R. Soc. B 361, 235–259 (2006).
Hosken, D. & Snook, R. How important is sexual conflict? Am. Nat. 165, S1–S4 (2005).
Rowe, L., Cameron, E. & Day, T. Escalation, retreat and female indifference as alternative outcomes of sexually antagonistic coevolution. Am. Nat. 165, S5–S18 (2005).
Hosken, D. J., Stockley, P., Tregenza, T. & Wedell, N. Monogamy and the battle of the sexes. Ann. Rev. Entomol. 54, 361–378 (2009).
Crudgington, H. S. & Siva-Jothy, M. T. Genital damage, kicking and early death. Nature 407, 855–856 (2000).
Hotzy, C. & Arnqvist, G. Sperm competition favours harmful males in seed beetles. Curr. Biol. 19, 404–407 (2009).
Blanckenhorn, W. U. et al. The costs of copulating in the dung fly Sepsis cynipsea. Behav. Ecol. 13, 353–358 (2002).
Hosken, D. J. & Price, T. Genital evolution: the traumas of sex. Curr. Biol. 19, R519–R521 (2009).
Rönn, J., Katvala, M. & Arnqvist, G. Coevolution between harmful male genitalia and female resistance in seed beetles. Proc. Natl Acad. Sci. USA 104, 10921–10925 (2007).
Siva-Jothy, M. T. Trauma, disease and collateral damage: conflict in cimicids. Phil. Trans. R. Soc. B 361, 269–275 (2006).
Carayon, J. in Monographs of the Cimicidae (ed. Usinger, R.) 81–87 (Entomological Society of America, Philadelphia, 1966).
Eberhard, W. G. Sexually antagonistic coevolution in insects is associated with only limited morphological diversity. J. Evol. Biol. 19, 657–681 (2006).
Jennions, M. D. & Kelly, C. D. Geographical variation in male genitalia in Brachyrhaphis episcope (Poeciliidae): is it sexually or naturally selected? OIKOS 97, 79–86 (2002).
Langerhans, R. B., Layman, C. A. & DeWitt, T. J. Male genital size reflects a trade-off between attracting mates and avoiding predators in two live-bearing fish species. Proc. Natl Acad. Sci. USA 102, 7618–7623 (2005).
Ryan, M. J. A Taste for the Beautiful: The Evolution of Attraction (Princeton Univ. Press, Princeton, 2018).
Wessells, H., Lue, T. F. & McAninch, J. W. Penile length in the flaccid and erect states: guidelines for penile augmentation. J. Urol. 156, 995–997 (1996).
Soto, I. M., Manfrin, M. H. & Hasson, E. Host-dependent phenotypic plasticity of aedeagus morphology in a pair of cactophilic sibling Drosophila species of the replete group (Diptera. Drosophilidae). J. Zool. Syst. Evol. Res. 46, 368–373 (2008).
Córdoba-Aguilar, A. Sensory trap as the mechanism of sexual selection in a damselfly genitalic trait (Insecta: Calopterygidae). Am. Nat. 160, 594–601 (2002).
Hosken, D. J., Martin, O. Y., Born, J. & Huber, F. Sexual conflict in Sepsis cynipsea: female reluctance, fertility and mate choice. J. Evol. Biol. 16, 485–490 (2003).
Morrow, E. H., Arnqvist, G. & Pitnick, S. Adaptation versus pleiotropy: why do males harm their mates? Behav. Ecol. 14, 802–806 (2003).
Kingsolver, J. G. et al. The strength of phenotypic selection in natural populations. Am. Nat. 157, 245–261 (2001).
Lande, R. & Arnold, S. J. The measurement of selection on correlated characters. Evolution 37, 1210–1226 (1983).
Arnold, S. J. & Wade, M. J. On the measurement of natural and sexual selection: theory. Evolution 38, 709–719 (1984).
Arnold, S. J. & Wade, M. J. On the measurement of natural and sexual selection: applications. Evolution 38, 720–734 (1984).
We thank Michelle Taylor for the box 2 analysis and many colleagues for discussion of genital evolution.
Nature Reviews Urology thanks P. Brennan, Y. Kamimura, and the other anonymous reviewer(s) for their help with the peer review of this manuscript.
The authors declare no competing interests.
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Hosken, D.J., Archer, C.R., House, C.M. et al. Penis evolution across species: divergence and diversity. Nat Rev Urol 16, 98–106 (2019). https://doi.org/10.1038/s41585-018-0112-z
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