 In view of the many interpretations of Lamarck’s views that have emerged since the most developed presentation of his theory in his 1809 Philosophie Zoologique (Zoological Philosophy), the primary features of Lamarck’s reflections need to be carefully detailed. In most fundamental terms, his theory of species change was tied to his reversal of the taxonomic ordering of forms originally presented in his early systematic arrangements. In his original classifications, these groups were ordered in a linear series that began with the most complex invertebrates forms (cephalopods) and terminated in the least organized (infusorians). By 1800, Lamarck decided that this ordering was artificial, and that the “natural” arrangement was from simple to complex. The evolutionary theory he subsequently developed involved the claim that this new order of arrangement was also the historical sequence by which forms had been generated one from another over time.