All the Better to Track You With, My Dear
by Robert H. Gargett
Hominin morphology says nothing on its own about its adaptive underpinning. Instead, we human palaeontologists must interpret evolutionary significance as best we can. The Neanderthal face is an enduring example of the difficulty that confronts us when trying to infer the selective advantage that gave rise to a structure or a set of related structures.
|Forbes Quarry Homo neanderthalensis and a recent Homo sapiens (illustration from Rae, et al 2011)|
In the spirit of widening the range of possibilities for the selective pressures that gave rise to the Neanderthal face, in this paper I use as a jumping-off point the isotopic analyses of Bocherens and his colleagues (e.g. 1999). Bocherens has shown us that the Neanderthal's bone chemistry is almost identical with that of carnivores and not at all like that of herbivores or other great apes. Using that knowledge as a springboard, I argue that the face of H. neanderthalensis took on its distinctive morphology in response to a phyletic transition from ominvory to carnivory. Indeed, I propose that the distinctive morphology and size of the Neanderthal nasal aperture, the orbits, the infraorbital foramina, and the infraorbital portion of the maxillae came about in support of a reassertion of the olfactory sense when compared with the trend in Primate evolution and the state of olfaction in the other great apes, extant and extinct. In lay terms, the Neanderthals and their predecessors (or antecessors, as the case may be) were growing an ever-larger snout—to enable them to succeed at a trophic level quite different from that of earlier, contemporary, and later members of Hominina.
The size and evolutionary significance of the mid-facial region in the Neanderthals has been the subject of scholarly discourse almost from the earliest discoveries a century and a half ago. When viewed in norma frontalis the salient facial features are the orbits and the nasal aperture, which are gargantuan openings when compared to the measly recent-human exponent. In large part I think the eye sockets have been overlooked, but for generations the Neanderthal's nasal aperture has been viewed as an adaptation to the cold air of the periglacial environment. To others it is the result of a rigorous ecological niche and the combination of biomechanical factors imposed by anterior dental loading (suggested by the distinctive wear patterns on Neanderthal incisors, among others). Neither explanation is satisfactory, and never has been. The cold adaptation thesis never had empirical support, as is correctly pointed out in a recent paper by Rae, Koppe, and Stringer (2011). As for the biomechanical hypothesis, there is hardly a bony or chitinous structure in the animal realm that is not present as a result of biomechanical necessity. It's a proximate explanation that begs for an ultimate explanation.
|The "Old Man" from La Chapelle-aux-Saints (illustration found on web...if you know the correct attribution, please let me know)|