Relationships between the hard and soft dimensions of the nose in Pan troglodytes and Homo sapiens reveal the nasal protrusions of Plio-Pleistocene hominids

Abstract

By identifying similarity in bone and soft tissue covariation patterns in hominids, it is possible to produce facial approximation methods that are compatible with more than one species of primate. In this study, we conducted an interspecific comparison of the nasomaxillary region in chimpanzees and modern humans with the aim of producing a method for predicting the nasal protrusions of ancient Plio-Pleistocene hominids. We addressed this aim by first collecting and performing regression analyses of linear and angular measurements of nasal cavity length and inclination in modern humans ( Homo sapiens; n = 72) and chimpanzees ( Pan troglodytes ; n = 19), and then by performing a set of out-of-group tests. The first test was performed on two subjects that belonged to the same genus as the training sample, i.e., Homo ( n = 1) and Pan ( n = 1), and the second test, which functioned as an interspecies compatibility test, was performed on Pan paniscus ( n = 1), Gorilla gorilla ( n = 3), Pongo pygmaeus ( n = 1), Pongo abelli ( n = 1), Symphalangus syndactylus ( n = 3), and Papio hamadryas ( n = 3). We identified statistically significant correlations in both humans and chimpanzees with slopes that displayed homogeneity of covariation. Joint prediction formulae were found to be compatible with humans and chimpanzees as well as all other African great apes, i.e., bonobos and gorillas. The main conclusion that can be drawn from this study is that regression models for approximating nasal projection are homogenous among humans and African apes and can thus be reasonably extended to ancestors leading to these clades.