Steve Gould (1980), in his paper on the promise of paleobiology as a nomothetic evolutionary discipline, sets the nomothetic, the search for general rules or laws, against the idiographic, the detailed description of unique events. Gould (1980) notes that all idiographic events have nomothetic undertones. I agree, but go further. For me, unique events in the history of life not only have nomothetic undertones, but have nomothetic underpinnings. Here I outline these underpinnings for perhaps the most dramatic event seen in the fossil record, the Cambrian “explosion” of bilaterian animals. I am most interested in the rapid increases in...

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