Original:  What gives this concept of 'academic history' its own historicity, or "cubbyhole in time", superseded by progress, is that an academic history was intended to be definitive even though its subject matter, unlike the marine biology mentioned above, was not objective.
Revised:  What gives this concept of "academic history" its own historicity, or "cubbyhole in time", superseded by progress, is that an academic history was intended to be definitive even though its subject matter, unlike the marine biology mentioned above, was not objective.
Edit intent: fluency