Among associations other than those of family relationship by means of which the process of displacement is brought about, those depending on mental or physical similarity are probably the most important; of all the available methods of transference, they are too, in many respects, the easiest, most natural and the least liable to cause pathological aberrations of development. There can be little doubt, too, that the frequent occurrence of the displacement of the love impulse along these lines constitutes a factor of very considerable sociological and historical importance. The tendency to choose a mate resembling in some essential aspects--mental or physical--one's own nearest relatives, must, for good or evil, act as a potent means of preserving the purity of individual types and of family, national or racial qualities; especially when, as may often happen, there is added to the influence of this factor that of the narcissistic element of love to which we have already referred. So long as the associative link which conditions the displacement is one that has some correspondence to reality, the closer the unconscious identification of the sexual partner of adult life with the object loved in infancy, the more likely will it be for this partner to possess hereditary qualities similar to those of the lover himself, and the greater therefore, in all probability, the resemblance of the ensuing offspring to their parents. [Sidenote: Name] Among the similarities of a less essential kind which may assist in the process of displacement, those of _name_ are apt to play an important but subtle part and one that is very liable to be overlooked or where observed, ascribed to coincidence rather than (as it more often should be) to the operation of unconscious mental factors[118]. They are in some respects a source of danger, inasmuch as they are concerned with relatively superficial characteristics[119] which have little to do with the real nature of the person selected, thus making easy the choice of otherwise unsuitable objects of affection. [Sidenote: Age] Similarities with the parents as regards _age_ often exercise some influence in early years and in the early stages of displacement, but in later life are less operative than, in view of the intensity of the parent fixation in some individuals, might perhaps be expected. This is probably due, to a large extent at any rate, to the fact already referred to, that the unconscious parent love of adult life has as its object the image of the parents as they appeared to the child in infancy; these image-parents being therefore of a considerably younger age than that which the real parents have actually attained by the time the child has reached maturity.