Heredity in Freud

One of the most basic aspects of Freud's thought is his move away from the hereditary in his thought on etiology and towards a comprehensive notion of sexuality. One might say that the biggest tendency in objections to Freud--whether they be scientific or cultural--take the form of trying to work against this move and resituate symptoms in a rich (genetic and neurophysiological) conception of heredity (one can see this in a recent article on the diagnosis of depression). And while this may be more correct--in whatever sphere, be it scientific or cultural--it must overlook a particular complication or wrinkle the direction of Freud's movement produces. Etiology, when not interpreted as a hereditary function (and interpreted in terms of sexuality), precisely calls for a rethinking of the concept of etiology. That is, it calls for the rethinking of cause, such that we can attribute the cause of a symptom with equal validity to that of heredity or psychology. In other words, Freud doesn't merely replace heredity with psychology or psycho-sexual disposition. He makes the first coextensive with the latter, such that we can never be totally sure which one is the real source of the symptoms.
We find this summarized in a great early paper (written in French to the students of Charcot, who rigorously interpreted symptoms as hereditarily caused), L'hérédité et l'étiologie des névroses (1896):

Our opinion of the etiological role of heredity in nervous illnesses ought decidedly to be based on an impartial statistical examination and not on a circular argument. Until such an examination has been made we ought to believe that the existence of acquired nervous disorders is just as possible as that of hereditary ones.
-Complete Psychological Works, III, 144, my emphasis.

Because the question is no longer about where the illness originated, since it can be just equally regarded as heredity or as acquired in the course or one's individual life (that is, as psychology), the question becomes one of how the symptoms are able to originate. More precisely, it is a question of the possibility of one cause being able to show up as the other. A whole dynamic here is missed if we simply go against Freud and try to ground him again in heredity. It is not a solely psychological dynamic, either: it is precisely the transit between the physical or hereditary and the psychical that is working itself here. And this is why conversion is such a key notion for the early Freud: the ability of anything to show up in a register where it should not be (the psychical in the physical) makes analysis stop looking for the original source and approach the issue more holistically. This doesn't mean that prescribing a drug won't change things: Freud is quick to actually recommend this where we are very sure we can determine a particular illness is heredity. It is just that we have to look at symptoms as only able to show themselves in part--even when they are already parts of a whole illness. We only get parts of the parts of illnesses--this is what it means to reevaluate etiology with this critique of heredity.