Sex at Dawn

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].”

9. BBC News online, July 16, 2003.

10. BBC News online, October 15, 2007.

11. Psychology Today, March/April 2001.

12. Barratt et al. (2009).

13. Hypothetically, one could try to falsify this hypothesis using data on testicular volume and sperm production from some of the societies we’ve discussed where sperm competition and partible paternity are in effect. To this end, we’ve contacted every anthropologist we could locate who has worked in the Amazon (or anywhere else with hunter-gatherers), but no one seems to have managed to gather these delicate data. Still, even if it were found that males in these societies showed higher testicular volume and sperm production, as our hypothesis predicts, definitive confirmation of the hypothesis would be precluded by the relative absence of the environmental toxins that are presumably at least partly responsible for testicular atrophy in industrialized societies.

14. BBC News online, December 8, 2006.

15. Diamond (1986).

16. W. A. Schonfeld, “Primary and Secondary Sexual Characteristics. Study of Their Development in Males from Birth through Maturity, with Biometric Study of Penis and Testes,” American Journal of Diseases in Children 65, 535-549 (cited in Short, 1979).

17. Harvey and May (1989).

18. Baker (1996), p. 316.

19. Bogucki (1999), p. 20.

Chapter 18: The Prehistory of O

1. Maines’s book has become an underground sensation. Written as a serious cultural history of the vibrator, the story

she tells is surprising and compelling. As we write, a play based on the book written by Sarah Ruhl (In the Next Room) is playing on Broadway. A National Public Radio story on the play is here: http://www.npr.org/templates/story/

story.php?storyId=20463597&ps = cprs.

2. Quotes taken from Margolis (2004).

3. See Money (2000). Interestingly, semen depletion is central to the ancient Taoist understanding of male health and sexuality as well. See, for example, Reid (1989).

4. On Baker Brown, see Fleming (1960) and Moscucci (1996).

5. Coventry (2000).

6. Although the clitoris is often referred to as “the only organ in the human body whose sole function is to provide pleasure,” there are two problems with this observation. First, if female orgasm (pleasure) is functional in the senses we outline (increases chances of fertilization, inspires vocalizations, and thereby promotes sperm competition), then there is clearly a purpose to the pleasure. Secondly, what about male nipples? Not all men find them to be a site of pleasure, but they are certainly highly enervated and serve no functional purpose.

7. Margolis (2004), pp. 242-243.

8. Ironically, according to archaeologist Timothy Taylor

(1996), this image of the Devil is thought to be derived from Cernunnos, the horned god, who was the Celtic translation of