From one point of view abnormalities occurring in these later stages are perhaps less serious than those which we considered in the earlier chapters, inasmuch as the regression is less complete; some degree of psychical emancipation from the parents being still preserved. Nevertheless these abnormalities may constitute a very grave hindrance to the general development and mental health of the individual and, in the case of the displacement of very intense affects, may give rise to consequences of a distinctly pathological order; while, on their more sublimated side, they have contributed much to some of the most important aspects of social life and culture. [Sidenote: Insufficient Displacement] [Sidenote: Displacement depending on family relationship] [Sidenote: Brother and sister] We have already in Chapter III studied some of the ways in which the displacement of the original love from parents to other persons takes place. If the displacement remains at a stage in which the associative link between the original and the later object of love is a very firm or close one, we may say that the development is incomplete, inasmuch as the individual's love is still to an undue extent on an infantile fixation. Of the various associative links which we have enumerated as being those of most frequent occurrence--mental or physical characteristics, age, circumstances of life, past history, family relationship etc., the last named is apt to play an especially important part in cases of arrested or regressive development. The displacement of love from parent to brother or sister may probably, as we have seen, be regarded as a normal transitory phase. The intensity of the attachment frequently aroused and the sexual nature which it often retains in the Unconscious right on into adolescent and adult life are vouched for, on the negative side, by the strength of the repressions raised against incestuous tendencies of this kind--repressions which are scarcely less severe than those directed against parent incest. Similarly, on the positive side, the true nature of the brother-sister relationship is often startlingly revealed by the process of psycho-analysis and is also shown by the study of legend, of literature and of the habits and customs of primitive peoples. [Sidenote: Cases where brother-sister incest has been permitted]