A brief review of shape, form, and allometry in geometric morphometrics, with applications to human facial morphology

We briefly and informally review the concepts of size, shape, and form and how they are estimated in geometric morphometrics using Procrustes analysis. We demonstrate how deformation grids and reconstructed shapes or forms can be used as powerful tools to visualize shape and form differences. Complex patterns of individual or group differences can be studied effectively by ordinations of shape space or form space. Allometry, the statistical relationship between size and shape, is estimated in geometric morphometrics by regression of the Procrustes shape coordinates on centroid size. We illustrate these methods by an application to human face shape. We reveal shape cues to body size in the adult male face, partly resembling ontogenetic allometry. Facial allometry might thus be an important confounding factor in studies of face perception and human mate choice.