Second Research Article
Relationships between the hard and soft dimensions of the nose in Pan troglodytes and Homo sapiens reveal the positions of the nasal tips of Plio-Pleistocene hominids
Article Abstract
By identifying homogeneity in bone and soft tissue covariation patterns in living hominids, it is possible to produce facial approximation methods with interspecies compatibility. These methods may be useful for producing facial approximations of fossil hominids that are more realistic than currently possible. 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 positions of the nasal tips of 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 performing a set of out-of-group tests. The first test was performed on four subjects that belonged to the same genus as the training sample, i.e., Homo (n = 2) and Pan (n = 2), 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. Prediction formulae combining these data 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 our set of regression models for approximating the position of the nasal tip are homogenous among humans and African apes, and can thus be reasonably extended to ancestors leading to these clades.
Fig 5. Reduced major axis regression formulae applied in 3D approximations of the nasal region for out-of-group test subjects in norma lateralis.
(A) H. sapiens: Anonymous 29-year-old male subject. (B) P. troglodytes: PRI-7895, 3-years-old. (C) P. paniscus: S9655, 4-years-old. (D) G. gorilla: PRI-Oki, 54-years-old. (E) G. gorilla: PRI-7902, 3-years-old. Scale Bar = 10 cm.
Fig 6. Reduced major axis regression formulae applied in 3D approximations of the nasal region for extinct hominids in norma lateralis.
(A) Australopithecus genus: Sts 5 (A. africanus) and MH1 (A. sediba).
(B) Paranthropus genus: KNM-WT 17000 (P. aethiopicus) and OH5 (P. boisei).
(C) Homo genus: KNM-ER 1813 (H. habilis), KNM-WT 15000, (H. ergaster / erectus), LES1 (H. naledi), Kabwe 1 (H. rhodesiensis/heidelbergensis), and Amud 1 (H. neaderthalensis/Neandertals).
Scale Bar = 10 cm.
There are homogenous relationships between the skull and the soft tissue parts of the nose in both chimpanzees and modern humans as members of the hominid clade. Regressions combining chimpanzee and modern human measurements have shown that this amalgam of data can produce statistically reliable nasal tip location prediction formulae. These prediction formulae can be applied to chimpanzees, modern humans, bonobos, and gorillas. Based on these results, we hypothesize that the same formulae are valid for approximating the position of the nasal tip for extinct hominids because their crania fit into the range of variability present in our sample of extant hominid species. More investigations are needed to produce prediction formulae for other measurements of the soft parts of the nose, such as the ala nasi. Our study does not support the view that the nose arose out of the face. Rather, it provides evidence supporting the alternative hypothesis that reductions in the size of the masticatory apparatus over time led to the external appearance of the anterior part of the nasal cavity in the genus Homo.