Fifteen years ago, when I went to a park at the edge of the Hudson, I couldn't step into the river--the sharp edges of open mussel shells were too thick underfoot. Nowadays at the park the creatures are mostly gone. Children splash happily in the shallows. Crumbled shells lie in the sediment, testament to the mussel's collapse. Humans are no different, Margulis believed. The implication of evolutionary theory is that Homo sapiens is just one creature among many, no different at base than P. vulgaris. We and they are controlled by the same forces, produced by the same processes, subject to the same fate. When Borlaug and Vogt stood on the tract of bad land, looking at the city, they were on the edge of the petri dish. Wizard or Prophet, it didn't matter. Homo sapiens, in Margulis's eyes, was just another briefly successful species.