Ontogeny, Phylogeny, Paleontology, and the Biogenetic Law

Nelson, G. (Department of Ichthyology, The American Museum of Natural History, New York, New York 10024) 1978. Ontogeny, Phylogeny, Paleontology, and the Biogenetic Law. Syst. Zool. 27:324-345. -The biogenetic law is restated in a falsifiable form: given an ontogenetic character transformation, from a character observed to be more general to a character observed to be less general, the more general character is primitive and the less general advanced. The law, as restated, may be generally valid. In any case, the ontogenetic argument is a valid direct technique of character phylogeny; the anatomical argument ("outgroup comparison") is an indirect technique; the paleontological argument is of uncertain status. Falsification -of all three types of arguments is explored in an analysis of L. Agassiz's concept of "threefold parallelism. " Neoteny is a falsifier not of the biogenetic law, but of character phylogeny-of all three arguments. Phylogenetic reconstruction in its entirety appears to be an extrapolation of the orderliness of development. [Ontogeny; phylogeny; paleontology; biogenetic law; parsimony; falsification; Agassiz. ] "When great changes occur in history, when great principles are involved, as a rule the majority are wrong" (Eugene Debs, 1918). "I have a simple faith that . semantic difficulties inspire 90% of any argument and that, when these are sorted out, both sides are doing something right" (Stephen Gould, 1976). "When you believe in things you don't understand, then you suffeT; superstition ain't the way" (Stevie Wonder, 1972). During the history of science there occur periods of disagreement and debate. One side of the debate sometimes emerges victorious, as for example uniformitarianism over catastrophism in geology. At other times, both sides lose, when subsequent history renders the entire debate irrelevant, as for example the debate among preformationists (spermatists vs. ovists). The last 25 years has been a period of debate among systematists. The debate has concerned basic principles of systematics (phenetics, phyletics, gradistics, etc.) and shows no sign of ending. At present, there are authors who claim that victory will be achieved in favor of some particular point of view, and others who claim that the entire debate was, is, and will continue to be, irrelevant. Of the latter authors, there are those who claim that the debate is irrelevant for systematics, and others who claim that the irrelevant factor is systematics itself. In short, all possible viewpoints seem represented. With respect to the current debate, and the future progress of science, wherein lies the relevance of systematics? In order to answer, a person must have some idea of what is being debated-the basic issues. Attaining a clear idea of the basic issues is a formidable task, as anyone who has read through the first 25 volumes of Systematic Zoology will readily admit. There are times when I wonder if there really are any basic issues, and at those times the debate seems to be over the question whether there need to be some. At other times I think that one basic issue concerns evolution and its bearing on systematics and classification. This is not a simple issue. Let me simplify it. According to the phylogenetic school, one objective of the systematist is clear: to search out shared advanced characters ("synapomorphies"), which can be used to define groups and subgroups, and which specify the nature of evolution insofar as its results are known to be orderly. The problem with this objective is