It is evident that certain genes which either initially or ultimately have beneficial effects may at the same time produce characters of a non-adaptive type, which will therefore be established with them. Such characters may sometimes serve most easily to distinguish different races or species; indeed, they may be the only ones ordinarily available, when the advantages with which they are associated are of a physiological nature. Further, it may happen that the chain of reactions which a gene sets going is of advantage, while the end-product to which this gives rise, say a character in a juvenile or the adult stage, is of no adaptive significance.