In a letter to the editor in the American Journal of Medical Genetics, two authors suggest that the story of Adam’s rib being the humble beginnings of Eve is the result of a mistranslation. In reality, they suggest, the story is an explanatory myth for why humans are one of the few mammals lacking a baculum, or penile bone.
“Congenital Human Baculum Deficiency: The Generative Bone of Genesis 2:21-23,” Scott F. Gilbert & Ziony Zevit, American Journal of Medical Genetics, May 2001, Vol. 101, pp. 284-285. The authors from Swarthmore College and American Jewish University write:
Our opinion is that Adam did not lose a rib in the creation of Eve. Any ancient Israelite (or for that matter, any American child) would be expected to know that there is an equal (and even) number of ribs in both men and women. Moreover, ribs lack any intrinsic generative capacity. We think it is far more probable that it was Adam’s baculum that was removed in order to make Eve. That would explain why human males, of all the primates and most other mammals, did not have one. The Hebrew noun translated as “rib”, tzela (tzade, lamed, ayin), can indeed mean a costal rib. It can also [...] be used to indicate a structural support beam. Interestingly, Biblical Hebrew, unlike later rabbinic Hebrew, had no technical term for the penis and referred to it through many circumlocutions. [...]
A rib has no particular potency nor is it associated mythologically or symbolically with any human gen- erative act. Needless to say, the penis has always been associated with generation, in practice, in mythology, and in the popular imagination. Therefore, the literal, metaphorical, and euphemistic use of the word tzela make the baculum a good candidate for the singular bone taken from adam to generate Eve.