I need some help for coming up with some reasons as to why certain cell signaling pathways are preserved in species over the course of evolution. Why would natural selection favor a certain basic, primitive pathway when more advanced pathways have been developed in higher organisms?
For example, a particular wound-healing pathway, the ERK (extracellular signal-regulated kinase) cascade pathway induces repair and regeneration of an asceptically damaged cuticle in fruit flies. ERK works by inducing the activity of the Grainy Head transcription factors to regenerate the cross-linking proteins of the skin. The Grainy Head transcription factors are also present in mice. Why is this so? Is it because ERK and Grainy Head are reliable back-up pathways in case other more advanced pathways fail? Are there other reasons? Thanks.
I can not provide you with a certain answer, but I'm not sure anybody can. This is somewhat outside my ordinary field (cancer therapy). On the other hand I think it is wise to apply Occam's razor on a question like this and not make ...