I just came across, randomly, through one of those serendipitous and unexpected JSTOR journeys, a 1966 article by ornithologist Herbert Friedmann on “The Significance of the Unimportant in Studies of Nature and of Art,” which seems to anticipate a core theme of Carlo Ginzburg’s famous essay on “Clues,” including its reliance on Morelli, although Friedmann compares art-historical methods to natural-history taxonomy rather than to medical diagnosis. A quick web search suggests that these two authors are not often cited together, but when they are it is where you might suspect: in works on biosemiotics, like this one by Thomas Sebeok.