This is the most general theme about mainstream views, be they past or present, on the operations of the world absent humans. The theme may discuss widely held existential claims, moral precepts, or views on human nature. It may particularly discuss scientific, religious, philosophical, artistic, and humanist views on the nature of reality.

Notes:
A view of reality is "mainstream" when it is broadly accepted in society. Fringe notions belong in "alternate reality". The societies falling under the scope of this theme are ones that presently exist on the face of the earth, and past societies the world views of which are reasonably well understood.

References:
https://en.wikipedia.org/wiki/Nature