Cellular oncogenes as the ancestors of endocrine and paracrine growth factors and their evolutionary relic status in vertebrates.

Contrary to the popularly held view, genes that have lost their usefulness to the host organism may continue to encode proteins for 50 million years or longer. Accordingly, precisely regulated expression of genes can not be taken as proof of their indispensability. My view is that multitudes of oncogenes of vertebrates are evolutionary relics harking back to the days of invertebrate ancestors in which embryogenesis was still a cell autonomous process. Parts of certain oncogene coding sequences originated from repeats of base oligomers whose numbers of bases were not multiples of three. Thus, these segments are still endowed with a measure of immortality in that they are impervious to normally very deleterious base substitutions, insertions, and deletions.