23. The New Yorker, June 26, 2006, p. 76.
1. This quote is taken from a debate between Gould on one side and Steven Pinker and Daniel Dennett on the other. Well worth reading, if you like high-brow discussion with plenty of low blows, is “Evolution: The Pleasures of Pluralism,” The New York Review of Books 44(11): 47-52.
2. Potts (1992), p. 327.
1. Miller (2000), p. 169.
2. Though not always, as other factors can influence body-size dimorphism, apart from the intensity of male-male mating conflict. See Lawler (2009), for example.
3. Male Australopithecus (between three and four million years ago) are thought to have been about fifty percent larger than females. Recent papers suggest Ardipethicus ramidus, another supposed human ancestor (thought to be a million or so years older than Australopithecus) was closer to our 15 to 20 percent levels. But keep in mind that the much-ballyhooed reconstruction of Ardipethicus ramidus relied upon bits and pieces of many different individuals, so our sense of body size dimorphism 4.4 million years ago is based upon educated guesses, at best (White et al., 2009).
4. Lovejoy (2009).
5. http://www.psychologytoday.com/articles/200706/ ten-politically-incorrect-truths-about-human-nature.
6. Supplemental note. On sexual selection in relation to monkeys. Reprinted from Nature, November 2, 1876, p. 18. http://sacred-texts.com/aor/darwin/descent/dom25.htm.
7. As we’ll discuss in the next chapter, the genital echo theory posits that women developed pendulous breasts so that the cleavage would mimic the (is there a scientific term for this?) butt-crack that so enticed our primate ancestors. Following that line of reasoning, some argue that fancily named lipstick serves to re-create the bright red “hinder ends” that so perplexed poor Darwin.
8. See Baker and Bellis (1995) or Baker (1996) for the sperm-team theory.
9. Hrdy (1996) is a wonderfully erudite and engaging discussion of how some of Darwin’s personal sexual hang-ups are reflected still in evolutionary theory.
10. Supplemental note. On sexual selection in relation to monkeys. Reprinted from Nature, November 2, 1876, p. 18. http://sacred-texts.com/aor/darwin/descent/dom25.htm.
1. de Waal (2005), p. 113.
2. In Barkow et al. (1992), p. 299.
3. Barash and Lipton (2001), p. 141.
4. Pochron and Wright (2002).
5. Wyckoff et al. (2000). Other research looking into primate testicular genetics has reinforced the impression that ancestral human mating behavior more closely resembled the promiscuity of chimps than the one-male-at-a-time gorillas. See, for example, Kingan et al. (2003), who conclude that although “predicting the expected intensity of sperm competition in ancestral Homo is controversial, .we find patterns of nucleotide variability at SgI in humans to resemble more closely the patterns seen in chimps than in gorillas.”
6. Short (1979).
7. Margulis and Sagan (1991), p. 51.
8. Lindholmer (1973).
9. For more on this, see work by Todd Shackelford, particularly Shackelford et al. (2007). Shackelford generously makes most of his published work available for free download at http://www.toddkshackelford.com/publications/ index.html.
10. Symons (1979), p. 92. Although we probably disagree with half of his conclusions, and much of the science is out of date, Symons’s book is well worth reading for its wit and artistry alone.
11. Harris (1989), p. 261.
12. Sperm competition is an area of passionate debate. Space limitations (and quite possibly, readers’ interest) preclude us from a more thorough discussion—especially concerning the highly controversial claims of Baker and Bellis regarding sperm teams composed of specialized cells acting as “blockers,” “kamakaze,” and “egg-getters” For a scientific review of their findings, see Baker and Bellis (1995). For a popularized review, see Baker (1996). For a balanced discussion of the controversy written by a third party, see Birkhead (2000), especially pp. 21-29.
13. Data primarily from Dixson (1998).
14. See, for example, Pound (2002).
15. Kilgallon and Simmons (2005).
16. Some readers will argue that these conventions in contemporary pornography are expressions of female subjugation and degradation rather than eroticism. Whether or not this is the case (a discussion we’re going to sidestep at this juncture), one must still ask why it is being expressed in this way, with these images, given that there are so many ways of visibly humiliating a person. Some authorities believe the practice of bukkake originated as a way of punishing adulterous women in Japan—a somewhat less
Puritanical Scarlet Letter, if you will (see, for example, “Bake a Cake? Exposing the Sexual Practice of Bukkake,” poster presented at the 17th World Congress of Sexology, by Jeff Hudson and Nicholas Doong:
http://abstracts.co.allenpress.com/pweb/sexo2005/document/ 50214). If you don’t know what bukkake is, and you’re even slightly prone to being offended, please forget we even mentioned it.
1. Frans de Waal suspects that bonobos have longer penises than humans, at least relative to body size, but most other primatologists seem to disagree with his assessment. In any case, there is no question that the human penis is far thicker than that of any other ape, in absolute terms or relative to body size, and far longer than that of any primate not clearly engaged in extreme sperm competition.
2. Sherfey (1972), p. 67.
3. One species of gibbon, the black-crested gibbon (Hylobates concolor), does in fact have an external, pendulous scrotum. Interestingly, this type of gibbon may also be exceptional in not being strictly monogamous (see Jiang et al., 1999).
4. Gallup (2009) offers an excellent summary of this material.
5. Dindyal (2004).
6. http://news.bbc.co.uk/go/pr/fr/-/2/hi/health/7633400.stm 2008/09/24.
7. Harvey and May (1989), p. 508.
8. Writing in the Encyclopedia of Human Evolution, Robert Martin notes, “Relative to body size, humans have a very low value for rmax—even in comparison with other primates. This suggests that selection has favoured a low breeding potential during human evolution. Any model of human evolution should take this into account.” A low rmax value along with the very high levels of sexual activity typical of humans is yet another indication that sex has long functioned for nonreproductive purposes in our species.
Similarly, while Dixson (1998) characterizes the seminal vesicles of monogamous and polygynous primates (except the gelada baboon) as vestigial or small, he classifies the human seminal vesicles as medium—noting that “it is reasonable to propose that natural selection might have favoured reduction in size of the vesicles under conditions where copulation is relatively infrequent and the need for large ejaculate volume and coagulum formation is reduced.” He goes on to propose that “this might explain the very small size of the vesicles in primarily monogamous [primates].”