How seriously should we take "levels" of reality? I mean the parcellation of the universe into, say, the particle level, the chemical level, the cellular level, the organism, individual level, the social/ecological level etc?

Do levels interpenetrate?

Are these metaphysical matters or just pragmatic ones?

Stimulated by the great session on mental disorders just completed, hosted by @PessoaBrain , featuring Anneli Jefferson, @awaisaftab , @NicoleCRust , Alexey Tolchinky & @eikofried