Employing artificial materials to create simulations of nature, the 18 artists featured in UnNaturally explore the ways in which the boundaries between nature and culture are sometimes blurred. Works by Tim Hawkinson, I igo Manglano-Ovalle, Roxy Paine, Marc Quinn and Francis Whitehead play on our nostalgia for an idealized pre-industrial past in which man and nature coexisted harmoniously in an unspoiled landscape--the same nostalgia that has...