In the sprawling, splashy “New Humans” exhibition inaugurating New York’s newly expanded New Museum (sound new enough for you?), a mechanical apparatus quietly whirrs. This tumbler, by the artist Steffani Jemison, is slowly but surely agitating and refining dredged debris: glass, coins, stone.Having studied comparative literature as an undergraduate, Jemison often moves between writing and art in thoughtful if seemingly unlikely ways, as in her novella A Rock, A River, A Street