The reign of the sexual instinct and "perversions" already appear in the animal kingdom:
Perhaps the bonobo's most typical sexual pattern, undocumented in any other primate, is genito-genital rubbing (or GG rubbing) between adult females. One female facing another clings with arms and legs to a partner that, standing on both hands and feet, lifts her off the ground. The two females then rub their genital swellings laterally together, emitting grins and squeals that probably reflect orgasmic experiences. (Laboratory experiments on stump- tailed macaques have demonstrated that women are not the only female primates capable of physiological orgasm.)
Male bonobos, too, may engage in pseudocopulation but generally perform a variation. Standing back to back, one male briefly rubs his scrotum against the buttocks of another. They also practice so-called penis-fencing, in which two males hang face to face from a branch while rubbing their erect penises together.
The diversity of erotic contacts in bonobos includes sporadic oral sex, massage of another individual's genitals and intense tongue-kissing. Lest this leave the impression of a pathologically oversexed species, I must add, based on hundreds of hours of watching bonobos, that their sexual activity is rather casual and relaxed. It appears to be a completely natural part of their group life. Like people, bonobos engage in sex only occasionally, not continuously. Furthermore, with the average copulation lasting 13 seconds, sexual contact in bonobos is rather quick by human standards. De Waal, ‘Bonobo Sex and Society’
So, if we oppose Freud's simple model of sexual pleasure leaning on the self-preservative instinct and instead talk about how genital pleasure can activate or be displaced onto other parts of the body then we have new questions of how the 'organs' or parts are sources that can be chosen.
Furthermore, as Fenichel noted, these parts can also be activated by aggressive energy:
Let us begin with the first problem. When looking has become libidinized, so that the aim of the person who looks is not perception but sexual gratification, it differs from the ordinary kind of looking. Libidinal looking often takes the form of a fixed gaze, which may be said to be spastic, just as the act of running, when libidinized, is spastic. (Libidinization has the effect of impairing an ego-function.) (13)
Very often sadistic impulses enter into the instinctual aim of looking: one wishes to destroy something by means of looking at it, or else the act of looking itself has already acquired the significance of a modified form of destruction. Thus, for instance, the compulsion so frequently met with in women to look at the region of a man's genitals is really a modified expression of active castration-tendencies. It seems then that there are two tendencies which always or often determine the goal of the scopophilic instinct: (a) the impulse to injure the object seen, and (b) the desire to share by means of empathy in its experience. (11)
It is a well-known fact that when an organ is constantly used for purposes of erotogenic pleasure, it undergoes certain somatic changes.48 It happens that Freud was speaking of the eyes of persons in whom the scopophilic instinct is specially developed, when he said, 'If an organ which serves two purposes overplays its erotogenic rôle, it is in general to be expected that this will not occur without alterations in its response to stimulation and in innervation', i.e. of the physiological factors in general. From the point of view of research it is probably more useful, when studying myopia, to consider the somatic changes which take place in the eye in consequence of its being used for libidinal purposes than to regard the incapacity to see at a distance as a symbol of castration. We have an additional reason for thinking that we shall discover somatic-neurotic relations when we read further in Freud: 'Neurotic disturbances of vision are related to psychogenic as, in general, are the actual neuroses to the psychoneuroses; psychogenic visual disturbances can hardly occur without neurotic disturbances, though the latter surely can without the former.'50
What has ophthalmic medicine to say on the subject of myopia? We are told that it is caused by an elongation of the axis of the eyeball. This elongation is attributed partly to the external muscles of the eye and partly to general vegetative changes which alter the contour of the eyeball itself. It would seem, then, that incapacity to see distant objects has no psychic significance but is the involuntary, mechanical sequel to processes which either affect the external optic muscles or take place within the eyeballs. But what causes these processes? At all events the vegetative nervous system plays a decisive part in them, and the functioning of that system is, apart from various somatic factors, psychically determined. The question is this. We have seen that the constant use of the eye for the libidinal gratification of scopophilic impulses causes it actively to strain in the direction of objects, in order psychically to incorporate them. Is it not possible that this may finally result in a stretching of the eyeball?
We recognize that this is putting the problem very crudely. Of course an exact knowledge of the ways in which such stretching may occur would be necessary to explain why many people in whom the scopophilic instinct is peculiarly strong are not in the least short-sighted. There is no difficulty about the converse fact, namely, that many short-sighted people (often those in whom the symptom is most pronounced) show no sign of a marked scopophilic tendency. There is no reason to suppose that every case of myopia is psychogenic. And, while the stretching of the eyeball may sometimes be due to the attempt to incorporate objects at the bidding of scopophilic impulses, in other cases the origin of the disability is undoubtedly surely somatic. (33-4)
Fenichel, O. (1937). The Scopophilic Instinct and Identification
I'll have to post more on this in the future, but Wilhelm Reich was the only fully materialist psychoanalyst and made the simple point that repression will never occur without suppression. The desires or emotions held back are felt, or have what he calls organ sensations, in that we aren't just angry but feel our 'blood begin to boil' we feel like we want to hit out, we feel a knot in our stomach in worrying about punishment, we feel aroused, etc. So, Reich would pair up a pattern of rigid muscles that are involved in holding back these feelings and which, in their rigidity, could receive the aggressive and sexual displacements of which Fenichel writes.