If these influences have made incest a common practice at one period of man's history, in what ways has this practice contributed to the tendency to incest found at a later date and at the present day? In view of the widespread (we are probably justified in saying universal) occurrence of this tendency, of the relative uniformity of its ultimate nature in spite of manifold differences of culture, training, and environment, of the great strength which it possesses even after ages of repression, there is not unnaturally a temptation to regard it as an innate factor in man's mental constitution, _i. e._, to assert that there is in man an hereditary tendency to direct his love and sexual inclination to those who are of his own blood or at any rate to those with whom he has been brought up and has been familiar since his infancy[245]. Possibly in the long ages in which man or his pre-human ancestors lived in relatively isolated families, this tendency was of advantage in the struggle for existence, in so much as it may have contributed both to more rapid multiplication and to the greater consolidation, and therefore greater safety and stability, of the family, as the most important social unit. The tendency to incest may thus be due ultimately to the action of natural selection; the long period during which incest was regularly practised may have established and ingrained it as a normal feature of the race and its persistence to-day may be due to the continuance of the hereditary disposition thus formed and thus consolidated. Apart from the direct influence of this hereditary factor however, a long period during which incest was habitual may have affected the tendency to incest at a later time through custom, law and tradition. These change but slowly in a primitive society, and, through their inertia, would tend to reinforce or maintain the hereditary factor, even when, owing to the action of other causes, incest may have been abandoned in the main in favour of exogamy. These influences may have kept alive the remembrance of, and desire for, incest, which would otherwise possibly have succumbed to the forces working to bring about its suppression. FOOTNOTES: [Footnote 226: _Cp._ in this connection Abraham, "Untersuchungen über die früheste prägenitale Entwicklungstufe der Libido", _Zeitschrift für ärztliche Psychoanalyse_, 1916, IV. Also Freud, "Sammlung kleiner Schriften zur Neurosenlehre", IV, 274.] [Footnote 227: "Social Psychology", 91.] [Footnote 228: _Cp_. T. Burrow, "The Genesis and Meaning of Homosexuality and its relation to the problem of introverted mental states." _Psychoanalytic Review_, IV. 272.]