New scientific evidence challenges a common perception that Neandertals — a close evolutionary relative to modern humans that lived 230,000 to 30,000 years ago — possessed exceptionally long faces.
Instead, a report authored by Erik Trinkaus, Ph.D., the Mary Tileston Hemenway Professor of anthropology in Arts & Sciences, shows that modern humans are really the “odd man out” when it comes to facial lengths, which drop off dramatically compared with their ancestral predecessors.
Trinkaus’ findings, which appeared in the July 8 issue of the journal Proceedings of the National Academy of Sciences (PNAS), are based on two critical skull measurements on fossilized specimens. His article, “Neandertal Faces Were Not Long; Modern Human Faces Are Short,” is available at the PNAS Web site, pnas.org.
Trinkaus’ main objective was to see how Neandertal faces stacked up against others in the evolutionary lineage: 179 “recent humans” (dating back to the 18th century); 26 Late Pleistocene early modern humans; 24 Neandertals; and 23 archaic human Neandertal predecessors.
His research has effectively established a baseline for future anthropologists to categorize evolutionary patterns as being ancestral (having traits similar to those present in a remote ancestor) or derived (traits that have undergone a recent change).
“Basically, the issue is whether the ‘big’ Neandertal face is simply something they inherited from their ancestors, or whether it is something that is uniquely derived for them — something that makes them divergent in human evolution,” Trinkaus said. “This was just a short paper to demonstrate that Neandertals, put in their proper evolutionary context, do not have big faces; as the title says, modern humans have short ones.”
In order to assess facial length, Trinkaus first measured the prosthion radius, or the distance that extends from the ear hole out to the roots of the incisors.
The second measurement, the mandibular superior length, is a projection of the linear distance from the middle of the condyles (a point on the jaw joint) to the midpoint between the incisors.
Together, the two measurements take into account how far the incisors project out relative to the core of the skull.
Data for older specimens — which are limited both in number and by degree of preservation — were taken from previously documented discoveries from around the world. For the recent humans, however, Trinkaus worked in a more hands-on fashion, spending a day measuring the skulls of 18th- and 19th-century “Old World humans” at the American Museum of Natural History in New York, which boasts the most geographically diverse sample of skeletons in North America.
After compiling the data for different groups of hominids, Trinkaus concluded that the Neandertal’s overall facial projection was, if anything, average for a Pleistocene epoch sample and was similar to or even modestly reduced from their non-Neandertal archaic predecessors.
He also noted that their size was only moderately greater than those of early modern humans, but principally contrasted with recent, late Holocene humans (humans of today). Thus, from an evolutionary standpoint, there was nothing uniquely derived about Neandertal face lengths.
Explaining the misconception
Still, Trinkaus sees several possible explanations for the misconception. First, the majority of the more complete Neandertal skulls that anthropologists have thus far unearthed happen to be those of large males, each of whose facial length scales with the rest of their body.
Trinkaus said there also is the influence of “time’s arrow” — that is, for most of the last century, Neandertals have been compared primarily with recent humans and not to their own predecessors. And quite simply, despite major discoveries over the last 40 years, no one had previously published a comprehensive study comparing Neandertal facial lengths to both recent humans and earlier ancestors.
“It was acceptable in 1950 to say Neandertals had big faces,” Trinkaus said. “It’s not acceptable in 2003.”
Yet another possible reason was illustrated by the intense media fervor surrounding the 1999 discovery of a juvenile skeleton from Portugal. The skeleton is basically early modern human but bears some distinctive Neandertal characteristics, raising the possibility of interbreeding.
Trinkaus asserts that the erroneous characterization that Neandertals had long faces may, at least in part, have been a way to distance ourselves from a more “primitive” evolutionary relation.
“Neandertals are the archaic humans that are closest to us — closest to us in time, closest to us in behavior and in many aspects of their anatomy,” Trinkaus said. “They’re very human but they’re not quite us, and many people have great difficulty accepting that we may be closely linked to the Neandertals.
“Their world-view does not allow them to accept it because it downplays the idea that modern humans are very unique, that modern humans are very special.”
So if Neandertals didn’t have long faces, what’s the significance of humans having short ones?
“As you go further back in time, the periods encompassed by a sample get bigger and bigger,” Trinkaus said. “Faces basically remain long or decreased very slightly, but with modern humans they get a whole lot shorter very quickly. So the question is, ‘Why did they get shorter?’ I don’t know.
“But the point of this paper was not to answer that question; it was to allow us to frame that question. Because previously the question was, ‘Why did Neandertals have long faces?’ And that’s the wrong question.
“The correct question is, ‘Why do modern humans have really short ones?'”