The biological level is a level within World 1 that emerged from its physical-chemical evolution over a vast tract of time, as a lifeless universe eventually gave rise to living organisms, such as those on earth.
This cosmological approach is directly opposed to any form of reductionism that argues that we can ultimately explain whatever comes later in the known universe in terms of what came before.
Against this, Popper argues that we should instead see the universe as "creative" and indeterministic, and as having given rise to genuinely new levels or realms - like biological life, "World 2" and "World 3" - that were not there from its beginning and which are not fully 'reducible' to (or fully explicable in terms of) what was there at its beginning.
The three worlds may be understood, in terms of this evolutionary and cosmological framework, as containing three categories of entity: These include the states and processes that we seek to explain by physics and by chemistry, and also those states and processes that subsequently emerge with life and which we seek to explain by biology.
In Popper's view, World 3 'objects' encompass a very wide range of entities, from scientific theories to works of art, from laws to institutions.
This includes abstract objects such as scientific theories, stories, myths and works of art.
Popperian cosmology rejects this essentialism, but maintains the common sense view that physical and mental states exist, and they interact.