I’m a new Minecrafter, and was wondering if new updates are backwards compatible. Specifically, will the new “Adventure Update” features (Beta 1.8) appear in existing worlds created with Beta 1.7 and earlier? Or will I need to create a new world for this version?
No, ruins and villages are generated with the world, not actively built. If that changes in a future update, then it might not be required then, but for now all new geographic features require you to generate new chunks.
The usual way of doing this is just making a new world with all new chunks, but if you walk to places that you haven’t yet, then new chunks will generate. (Potentially with new features.) It’s still recommended that you generate a new world though since you might have to walk a while to get to new parts, the boundary between versions might not line up right, and biomes might shift(especially with the addition of a new one), but if you haven’t explored much or really like it so far, it might be worth it.