A metric for the study of evolutionary trends in the complexity of serial structures

Little empirical work has been done to see what sort of patterns of change in morphological complexity occur in evolution, mainly because the complexity of whole organisms has been so hard to define and to measure. For serial structures within organisms, there are fewer difficulties; this paper introduces a set of complexity metrics that are designed especially for serial structures, and then explores some of the properties of the new metrics. Also, a principle proposed in the last century by Herbert Spencer, and offered recently in a new form by the thermodynamic school of evolutionary thought, predicts that complexity should increase in evolution as a consequence of the accumulation of perturbations. Here, simulations in which perturbations are introduced to ideal and real series of vertebral measurements show how the complexity increase predicted by Spencer's principle would be captured by the new metrics.