Why is self-consciousness desire?

This is about the transition from self-consciousness to desire in the Phenomenology of Spirit. The German text (unfortunately without italics) is here. Where I quote from the English I give the first few words of the German passage afterwards so you can locate it if you want to. There is a good German-English dictionary here.

First of all, what does Hegel mean by self-consciousness?

At para 164 (Miller edition) he says that:

it is a distinguishing of that which contains no difference, or self-consciousness. I distinguish myself from myself, and in doing so I am directly aware that what is distinguished from myself is not different [from me]. I, the selfsame being, repel myself from myself; but what is posited as distinct from me, or as unlike me, is immediately, in being so distinguished, not a distinction for me. It is true that consciousness of an ‘other’, of an object in general, is itself necessarily self-consciousness, a reflectedness-into-self, consciousness of itself in its otherness. The necessary advance from the previous shapes of consciousness for which their truth was a Thing, an ‘other’ than themselves, expresses just this, that not only is consciousness of a thing possible only for a self-consciousness, but that self-consciousness alone is the truth of those shapes.

es ist Unterscheiden des Ununterschiedenen, oder Selbstbewußtsein ...

At 166 he repeats the point:

In this there is indeed an otherness; that is to say, consciousness makes a distinction [between itself and its object - AC], but one which at the same time is for consciousness not a distinction.

Es ist darin zwar auch ein Anderssein ...

So self-consciousness as Hegel understands it is a standpoint, or 'configuration of consciousness', in which I conceive my object, i.e. that which is not-me, as myself. So it is contradictory. There is a contradiction between difference (the object is not me) and identity (the object it is me). He explicitly introduces desire as a solution to this contradiction at 167:

Hence otherness is for it [i.e. for the subject who occupies the standpoint of self-consciousness - AC] in the form of a being, or as a distinct moment; but there is also for consciousness the unity of itself with this difference as a second distinct moment. With that first moment, self-consciousness is in the form of consciousness [i.e. the standpoints discussed in chapters 1-3 - AC], and the whole expanse of the sensuous world is preserved for it, but at the same time only as connected with the second moment, the unity [Einheit = oneness] of self-consciousness with itself; and hence the sensuous world is for it an enduring existence which, however, is only appearance, or a difference which, in itself, is no difference [kein Sein hat = has no being].

Es ist hiemit für es das Anderssein, als ein Sein ...

I take it that 'the unity of self-consciousness with itself' means the identity of the self-conscious subject with its object. So the same contradiction is being restated. The subject is driven to resolve the contradiction by coming to see the object as distinct from itself in appearance but identical to it in essence.

The same passage continues:

This antithesis of its appearance and its truth has, however, for its essence only the truth, viz, the unity of self-consciousness with itself; this unity must become essential to self-consciousness, i.e. self-consciousness is Desire in general. Consciousness, as self-consciousness, henceforth [nunmehr = henceforth or now] has a double object: one is the immediate object, that of sense-certainty and perception, which however for self-consciousness has the character of a negative; and the second, viz. itself, which is the true essence, and is present [vorhanden = existent] in the first instance only as opposed to the first object.

This is obscure but my reading is that that desire is the subject's effort to resolve the contradiction between difference and identity in favour of the latter, i.e. to render the object thoroughly identical to the subject. The object is seen as double: in its appearance it is distinct from the subject but in its essence it is identical to the subject. So the appearance is 'negative': it is not what the object really is (for really the object is identical to the subject). In desire the subject aims to do away with the appearance and reduce the object to the subject.

At 174 he says something a bit different:

self-consciousness is thus certain of itself only by superseding this other that presents itself to self-consciousness as an independent life; self-consciousness is Desire. Certain of the nothingness of this other, it explicitly affirms that this nothingness is for it the truth of the other; it destroys the independent object and thereby gives itself the certainty of itself as a true certainty, a certainty which has become explicit for self-consciousness itself in an objective manner.

das Selbstbewußtsein hiemit seiner selbst nur gewiß, durch das Aufheben ...

(By the way the claim that the object of desire must be a living organism has been introduced at 168. I'll pass over this.)

Here what he says is that subject was certain that the object was 'nothing', i.e. was not genuinely distinct from itself , but by destroying the object it shows itself that this is the case. Previously the subject was 'certain of itself' (or 'self-certain'). Hegel uses this term to mean to refer to the initial stage of self-consciousness. So it just means that the subject conceived its object as itself. But now this certainty has become 'true' or 'explicit for self-consciousness itself in an objective manner'. In other words it has shown itself that its object is identical to itself.

The difference is that in 167 desire is portrayed as an effort to make the object identical to the subject, but in 174 desire it is portrayed as an effort to prove that the object is essentially identical to the subject. The first formulation seems to carry over to his later writings (the Philosophical Propadeutic and the Encyclopedia Philosophy of Mind).