Evolutionary paleontology and the science of form

Details Evolutionary paleontology and the science of form Evolutionary paleontology and the science of form

Apr 1970

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970esrv....6...77g&link_type=abstract

Earth Science Reviews, Volume 6, Issue 2, p. 77-119.

Biology

Quantitative Biology

Quantitative Methods

1

Scientific paper

A science of form is now being forged within evolutionary theory. It studies adaptation by quantitative methods, using the organism-machine analogy as a guide; it seeks to reduce complex form to fewer generating factors and causal influences. If a function can be postulated for a structure, then its optimum form, or paradigm (Rudwick, 1961), can be specified on mechanical grounds. The approach of a structure to its paradigm provides the elusive criterion of relative efficiency that any science of adaptation requires. Physical laws and forces also specify that form be adapted to the requirements of size (surface/volume relationships) and space (close packing criteria). When we cannot establish paradigms on deductive criteria, an experimental approach to form is appropriate. Idealized models are favored over actual specimens because they can be built to test predetermined factors. Paleontology need not remain solely a descriptive science based on observational methods, but may adopt the experimental techniques of explanatory procedures. It is inconceivable that each aspect of a complex form is the direct product of an individual genetic instruction. We can simplify, and thereby understand, the generation of apparent complexity by recognizing that physical forces directly influence shape and that a few simple rules can fashion some very intricate final products. These rules can be programmed; computers have simulated structures that bear remarkable correspondence to actual forms; the geometry of genetic instruction need be no more complex. The rules can be used to generate a range of potential form available to such structures as the coiled shell (Raup, 1966). Actual forms fill only a part of the total spectrum; their basic adaptation may be grasped when we realize why unoccupied areas are not utilized. Among inductive studies of ontogeny and phylogeny, univariate techniques display trends and rates of change for single characters; they have been applied recently to the periodic growth lines of fossil shells, providing thereby a paleontological input to geophysics. Bivariate procedures, as the inevitable Gryphaea story illustrates, have been plagued by errors of method. When properly applied, they serve well in the separation of species and sexual dimorphs; they are the standard tool of quantitative description. Multivariate methods are based on the more satisfactory premise that an organism grows and evolves as a set of interacting parts; interactions should be considered together, not abstracted as pairs. In the R-mode, these methods may detect interrelated character clusters, reduce the high dimensionality of a system to few interpretable directions of variation, and eliminate redundant variables. In the Q-mode, they provide an objective picture of phenetic differences among samples and specify how the measured characters produce these differences. The importance of a new methodology can be gauged by its impact on ideas of life's history. A quantitative and functional science of form suggests that parallelism and convergence are dominant phenomena, not mere taxonomic nuisances. Early in their history, most phyla display great diversity at high taxonomic levels. These are not classic adaptive radiations, but sets of competing experiments in basic design. Early experimentation is followed by standardization of the best mechanical designs. These are often improved in similar ways by many independent lineages. Standardization and improvement provide invertebrate life with a history; the Phanerozoic has not been a time of endless ecological variation on a static set of basic structures.

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