1 Serron: No, really, how do we know we're in our original timestream and not some alternate one?
2 Paris: The computer scans incoming media and cross-checks against our ship's extensive banks of historical information.
3 Serron: And why do spaceships routinely carry extensive historical data anyway?
4 Paris: In case we come across an alien planet with a culture that bears an uncanny resemblance to a period in Earth's history.
4 Serron: Ah, it all makes sense.

Yep. Future missions across the Galaxy to seek out new life and new civilisations should stock up on historians and linguists and literary scholars, rather than, say, biologists and chemists and geologists.