Quantification of morphological variability expressed by a “log sem” statistic: Examples from extant and extinct hominoid species (craniodental anatomy)

Abstract

Abstract In this review of a morphometric technique, conspecific pairwise comparisons are made between craniodental measurements of adult hominoid specimens (representing extant and extinct species), in least squares linear regression analyses which are associated with equations of the form y = mx + c, where m is the slope and c is the intercept. The log of the standard error of the m-coefficient (“log sem”) is a reflection of the degree of scatter around a regression line, related to variability in shape. The m-coefficient is a reflection of size. Regressions are undertaken when measurements of any specimen P are on the x-axis, and those of another (conspecific) specimen Q on the y-axis; and vice-versa. Respectively, mean log sem values of -1.61 ± 0.13 and − 1.62 ± 0.12 have been observed in the context of crania and dentition of extant (Holocene) Homo, Pan (chimpanzee) and Gorilla conspecifics. Values of circa − 1.61 also appear to be the case in conspecific comparisons of extinct Plio-Pleistocene hominins, notably Early Homo (Early Pleistocene), Paranthropus (also Early Pleistocene) and Pliocene Australopithecus. A mean log sem value of -1.61 ± 0.1 is confirmed as a reflection of a typical degree of morphological variability within hominoid species if not also in other taxa.