bone of contention. The cause of a dispute or discord. It refers specifically to a bone that is fought over by two or more dogs. The OED says that the term derives from the use of the word bone in an earlier phrase “to cast a bone between,” which they describe as an “allusion to the strife which a bone causes between dogs.”

“Bone of contention” has been in use for two centuries, though I doubt many people think of dogs when they use it. Use remains strong, as evident in a search of the New York Times archives, with eight occurrences in 2005. Essayist George Johnson, writing on God's place in science, had some fun with the phrase. “It was on the second day at Cambridge that enlightenment dawned in the form of a testy exchange between a zoologist and a paleontologist, Richard Dawkins and Simon Conway Morris. Their bone of contention was one that scholars have been gnawing on since the days of Aquinas: whether an understanding of the universe and its glories requires the hypothesis of a God.” Writing about scientists who work with bones opens the door. However, given that the bone of contention involves the Christian creation story, I cannot help but think also of the bone God supposedly borrowed from Adam to create Eve. Perhaps we could see that as a kind of Original Bone of Contention.