Widespread occurrence of tumors and the ability of tumor cells to differentiate in combination with their ability to express genes that are not expressed in normal tissues, may result in the emergence of new cell types in the evolution of multicellular organisms.
We suggest that tumors could be a sort of proving ground (or reservoir) for the expression of newly evolving genes that originate in the course of genome evolution in the DNA of germ cells (i.e., not in tumor cells themselves). The case in which the expression of a newly evolving gene in tumors results in the origin of a new function would be associated with the origin of new feedback and regulatory circuits, as in root nodules in legumes and macromelanophores in Xiphophorus fishes. Tumor cells would differentiate, resulting in a new cell type for the given multicellular species. This cell type would be inherited because of epigenomic mechanisms similar to those in preexisting cell types.
Populations of tumor-bearing organisms with genetically or epigenetically programmed tumors could represent the transition between established species of organisms at different stages of progressive evolution.
Experimental confirmation of the prediction concerning the expression of evolutionarily new and/or silent (neutrally evolving) sequences in tumor cells will be presented.