Italian to English Art/Literary Art, Arts & Crafts, Painting Realism

The context is the evolution of Realism and the entire sentence is this:
"L’esigenza di manifestare un principio di verità nell’approccio più diretto al **dato naturale** si insinua in maniera forse meno esplicita, ma altrettanto penetrante e significativa, anche nei dipinti di storia o di soggetto religioso di artisti formatisi in ambito accademico"


Please don't worry about the rest of the sentence, I am clear about all of it, except the two words I have requested. Even there, I am pretty sure I understand what is meant, but I am at a loss as to now it can be expressed.

Many thanks for suggestions.

Angela