I carried out a complex comparative neurochemical study of the translation machinery functioning in the brain cells of three conventionally "phylogenetically related" species of wild lumber voles (Clethrionomys glareolus, Clethrionomys frater and Clethrionomys gapperi). I found that the cytoplasm of vole brain cells contains one or more oligonucleotide (oligoribonucleotide) factors with molecular weight below 1.0 KD** which are capable of the complete and highly selective inhibition of translation directed by mRNAs which are species-specific templates isolated from analogical tissue (brain) of these so-called "closely related" organisms. This phenomenon was found for the first time using a special cell-free translation system (CFTS) of very different variants of composition consisting of the following main components: (1) post-mitochondrial supernatant (PMS); (2) total cytoplasmic poly(A)+ mRNA or a species-specific poly(A)+ mRNA isolated from the PMS by affinity chromatography on columns with the anti- mRNA1 -Fab-(CNBr)-Sepharose, or purified 9S globin or 11S histone specific mRNAs, respectively, and (3) a few samples of the CFTS containing the addition of high or low molecular weight cytosolic compounds isolated from S150 fraction by ultrafiltration in Diaflo UM2 membranes with an exclusion limit of 1.0 KD. All CFTS components listed were isolated separately from the brain tissue of each organism studied. A new complex way for constructing and using the CFTS provided enough evidence to suggest the existence of one or more special, and as yet uncharacterized, cytoplasmic oligoribonucleotide factors which efficiently block the cytoplasmic expression of "evolutionally renovated parts" of the genome. These factors seem to be powerful enough to suppress the translation of every mRNA template that is not part of the cell type containing the cytoplasmic suppressors mentioned. Thus they would block the translation of any "novel" mRNA molecules that might have arisen as a result of spontaneous nonlethal gene mutations. This is a case in which gene expression is blocked at the level of mRNA function in the cytoplasm. The origins implications of this finding are discussed.