Labels:book | bulletin board | reckoner | sky OCR: the Cambrian explosion represents an initial filling of the "ecological barrel" of niches for multicellular organisms, and any experiment found a space The barrel has never emptied since even the great mass extinctions left few species in each principal role and their occupation ecological space forecloses opportunity for fundamental novelties But an "internal' explanation based on genetics and development also seems necessary as complement the earliest multicellular animals may have maintained flexibility for genetic change and embryological transf formation that became greatly reduced as organisms "locked in" to a set of stable and successful designs. In any case this initial period of both internal and external flexibility yielded a range of invertebrate anatomies that may have exceeded ...
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