the practical consequence of the conditions obtaining in Darwin’s primal horde must be exogamy for the young males. Each of them might, after being driven out, establish a similar horde, in which the same prohibition upon sexual intercourse would rule owing to its leader’s jealousy.
Freud derives exogamy and the incest prohibition directly from the structural logic of the primal horde, treating the expelled sons’ dispersal as the originary moment of social and sexual law.
, Totem and Taboo, 1913thesis