Genuine Puzzles In Biology?

I found one hypothesis to explain this, from here*. The basic idea is that, in mammals, the control genes regulating the expression of cervical vertebrae also regulate the rate at which cells reproduce. Any significant change to these runs the serious risk of making you very cancer-prone. Apparently, experimental studies on mice show that changes in the expression of certain control genes increase the expression of both cervical ribs and cancers, and there is supposedly a high correlation between the appearance of cervical ribs and childhood cancers in humans.*It's an excerpt from Glbert, S. 2006, Dev Bio, A Companion to Developmental Biology