Genetical Aspects of Metrical Growth and Form in Animals

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Abstract
The ontogenesis of those genetic differences in form which are homeomorphic, that is, which can be expressed in terms of measurements, is considered. Particular stress is laid on the advantages of longitudinal (versus cross-sectional, static, and mixed) data, and on the necessity of adapting the method of analysis to the type of data. Bivariate and multivariate methods of analysis are discussed, and the analysis of simple allometry is treated in detail. No existing multivariate method is competent to deal with longitudinal data; a way of overcoming this is suggested. Work on single-gene and multiple-gene differences, and comparisons between related species, are critically examined. Instances in which the allometry line is simply shifted in position, without change in k (the coefficient of allometry) are common; well-established differences in k are relatively rare. When differences in k do occur, they often result in intersection of the allometry lines, or in convergence toward older ages. It is suggested that this results from the combined effects of genes which singly affect either position alone, or k. Evolutionary allometry is held to be a description of evolutionary trends, not an explanation of them in terms of growth. Theories of growth control and regeneration are discussed, and aspects which need reexamination using longitudinal methods of analysis are indicated.