Eberhard, Female Control, pp. 142—46, 204—45, 248—54.
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A similar conundrum pertains to the “function” of the male copulatory organ in birds. Most male birds do not have a penis—insemination is achieved through simple contact of male and female genital apertures—and therefore its occurrence in some birds would appear to be, from a functional standpoint, “superfluous” (which could perhaps also be said about its occurrence in all other species). Moreover, in those species that do have a phallus (about 3 percent of all birds), its precise role in ejaculation and transporting semen remains unclear (see King, A. S. [1981] “Phallus,” in A. S. King and J. McLelland, eds., Form and Function in Birds, vol. 2, pp. 107—47 [London: Academic Press]; Briskie, J. V., and R. Montgomerie [1997] “Sexual Selection and the Intromittent Organ of Birds,” Journal of Avian Biology 28:73-86). In ratites such as Ostriches, Rheas, and Emus, as well as in Ducks and Geese, for example, the penis does not have an orifice connected to the male’s internal reproductive organs, and he simply ejaculates through his cloaca (at the base of the penis) as do all other male birds without a phallus. Although it carries a groove on its outside surface that may help direct semen during penetration, the penis does not transport semen internally. Moreover, in some birds such as buffalo weavers, the phallus has no such groove whatsoever (nor any internal ducts) and its role in sperm transport is even less clear. Consequently, the phallus’s reproductive “function” in these species is nearly as puzzling to biologists as that of the clitoris—the possibility that it could give sexual pleasure (to male and/or female) is rarely, if ever, even considered. Indeed, it is perhaps just as appropriate to speak of a male “clitoris” as it is of an actual “penis” in these cases, since the anatomy and function(s) of this organ may not be directly related to insemination (i.e., sperm transport). In addition, display of the phallus may also be an important element of courtship (as opposed to copulatory) activity in some species, as in the male Ostrich’s “penis-swinging” ceremony (Sauer and Sauer 1966:56-57) and possible penile displays in the white-billed buffalo weaver (Birkhead, T. R., M. T. Stanback, and R. E. Simmons [1993] “The Phalloid Organ of Buffalo Weavers Bubalornis,” p. 330, Ibis 135:326-31).
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Scientists who have recognized that sexual pleasure (or related aspects such as sexual arousal, gratification, or libido, and/or sexual, affectionate, or “erotic” attraction) may play a significant role in homosexual and /or heterosexual interactions include: primates (Wolfe, “Human Evolution and the Sexual Behavior of Female Primates,” p. 144; Vasey, “Homosexual Behavior in Primates,” p. 196); Bonobo (Kano 1992:195-96, 1990:66; Thompson- Handler et al. 1984; de Waal 1995:45—46, 1997:1,4,104, 111, 158); Orang-utan (Maple 1980: 158—59); Rhesus Macaque (Hamilton 1914:317-18; Akers and Conaway 1979:78-79; Erwin and Maple 1976:13); Japanese Macaque (Vasey 1996); Stumptail Macaque (Chevalier-Skolnikoff 1976:525); Killer Whale (Rose 1992:116-17); Gray Whale (Darling 1978:60; 1977:10); Northern Elephant Seal (Rose et al. 1991:186); African Elephant (Buss 1990:20); Silver Gull (Mills 1994:57—58); Laughing Gull (Hand 1981:139-40); Sage Grouse (Scott 1942:495). See also M. O’Neil’s and J. D. Paterson’s replies to Small (Small, M. F. (1988) “Female Primate Sexual Behavior and Conception: Are There Really Sperm to Spare?” pp. 91-92, Current Anthropology 29:81—100), and P. Vasey’s recent comments in Adler, T. (1996) “Animals’ Fancies: Why Members of Some Species Prefer Their Own Sex,” Science News 151:8-9.
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Birkhead, T. (1995) “The Birds in the Trees Do It,” BBC Wildlife 13(2):46-50; Brown-headed Cowbird (Rothstein et al. 1986:127-28).
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For some specific examples, see Marais 1922/1969:196-97 (Savanna Baboon); Fradrich 1965:379 (Warthog); Greenhall 1965:450 (Vampire Bat); Kear 1972:85-86 (Swans); Kharitonov and Zubakin 1984:103 (Black-headed Gull), Coulson and Thomas 1985:20 (Kittiwake); Nuechterlein and Storer 1989:341 (Grebes); Szekely et al., “An Evolutionary Approach to Offspring Desertion in Birds,” pp. 272—73.
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Common Murre (Birkhead and Nettleship 1984:2123-25).
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Virtually any of the references provided in the preceding notes will offer a sense of the ongoing debate and confusion about the “function” of each of these phenomena. For further examples, see: Adoption—Hansen, T. F. (1995) “Does Adoption Make Evolutionary Sense?” Animal Behavior 51: 474-75.
Nonreproductive copulations—Hatchwell 1988 (Common Murre); Small, “Female Primate Sexual Behavior and Conception.”
Multiple copulations—Gowaty, P. A. (1996) “Battles of the Sexes and Origins of Monogamy,” in J. M. Black, ed., Partnerships in Birds: The Study of Monogamy, pp. 21-52 (Oxford: Oxford University Press); Hunter, F. M., M. Petrie, M. Otronen, T. Birkhead, and A. P. Moller (1993) “Why Do Females Copulate Repeatedly With One Male?” Trends in Ecology and Evolution 8:21 -26; Petrie, M. (1992) “Copulation Behavior in Birds: Why Do Females Copulate More Than Once with the Same Male?” Animal Behavior 44:790-92.
Infanticide—Hrdy, S. B., C. Janson, and C. van Schaik (1994/1995) “Infanticide: Let’s Not Throw Out the Baby with the Bath Water,” Evolutionary Anthropology 3:151-54; Sussman, R. W., J. M. Cheverud, and T. Q. Bartlett (1984/1985) “Infant Killing as an Evolutionary Strategy: Reality or Myth?” Evolutionary Anthropology 3:149-51; Small, “Female Primate Sexual Behavior and Conception.”
Sex segregation (including migratory)—Miquelle et al. 1992 (Moose); Myers, J. P. (1981) “A Test of Three Hypotheses for Latitudinal Segregation of the Sexes in Wintering Birds,” Canadian Journal of Zoology 59:1527-34; Stewart and DeLong 1995 (Northern Elephant Seal).
Masturbation—Baker, R. R., and M. A. Bellis (1993) “Human Sperm Competition (Ejaculate Adjustment by Males and the Function of Masturbation,” Animal Behavior 46:861-85; Wikelski, M., and S. Baurle (1996) “Pre-Copulatory Ejaculation Solves Time Constraints During Copulations in Marine Iguanas,” Proceedings of the Royal Society of London, Series B 263:439-44.
On a related point, a number of insightful analyses of otherwise puzzling aspects of sexual and reproductive behavior are now being offered by two relatively recent (and complementary) strains in biological thinking. One of these is the theory of “sperm competition,” which contends that reproductive anatomy, physiology, and behavior are fundamentally shaped by the phenomenon of sperm from different males competing for fertilization by being present simultaneously in the female’s reproductive tract. The other is the theory of “cryptic female choice,” which argues that females themselves exert considerable influence on paternity after mating takes place by controlling whether and how sperm is utilized for fertilization. However, the complete absence of any discussion of sexual pleasure in these analyses (even where human beings are concerned) is notable. Not only is sexual pleasure as a “motivating force” compatible with many “sperm competition” and “cryptic female choice” analyses (and should therefore be considered as an important cofactor), it also offers significant insights into phenomena that continue to elude even these approaches (such as the extraordinarily high copulation rates of monogamous raptors, or mating far in advance of sperm storage periods in birds, or extrapair copulations with nonfertilizable females). For some discussion of these theories, see Baker and Bellis, Human Sperm Competition; Birkhead and Moller, Sperm Competition in Birds; Ginsberg and Huck, “Sperm Competition in Mammals”; Smith, ed., Sperm Competition and the Evolution of Animal Mating Systems; Eberhard, Female Control; Birkhead and Moller, “Female Control of Paternity.” For a critique of the general male-centeredness of most sperm-competition studies, see Gowaty, P. A. (1997) “Principles of Females’ Perspectives in Avian Behavioral Ecology,” pp. 97-98, Journal of Avian Biology 28:95- 102. For additional observations on the limitations of sperm competition (and sexual selection) theory as applied to species such as Oystercatchers, see Ens (1998:637).
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On the “function” of kissing in various species, see Common Chimpanzee (Nishida 1970:51-52); Orang-utan (Rijksen 1978:204-6); Squirrel Monkey (Peters 1970); West Indian Manatee (Moore 1956; Hartman 1979:110). For similar analyses applied to human kissing in various cultures, see Eibl-Eibesfeldt, I. (1972) Love and
