Some of our bones are easy to see. The zygomatic bones that give our cheeks shape, the delicate phalanges of our fingers, and the bony bulbs that are our kneecaps all stand out from beneath the flesh. But the hyoid bone is hidden.
Even if you’re looking at a study skeleton in a museum or doctor’s office, the hyoid is easy to miss. On the replica skeleton standing next to my desk, the U-shaped bone is hiding behind the lower jaw and is anchored to the fourth neck vertebra by wire. It needs the artificial connection because, in our bodies, the hyoid has no bony bridge to the rest of the skeleton. Instead, the hyoid is an anchor among scaffolds of flesh, supported by and providing support for the enveloping soft tissues.
And while this bone might not come up in day-to-day conversation, the hyoid has been critical to an argument about speech. The osteological horseshoe is an attachment point for muscles of the tongue, larynx, and pharynx. Without this bone, we wouldn’t be capable of making the symphony of sounds we use to help put our ideas into other people’s heads. That’s why the hyoid has played such a prominent role in the ongoing debate over whether our close Neanderthal relatives could talk and sing.
The argument breaks down like this. Even though we belong to the same species – we interbred, after all – anthropologists can still differentiate Neanderthals on the basis of their bony anatomy. Among the ways they differed from modern people was a thinner hyoid bone that may have rested a little higher in the throat. According to anthropologists Philip Lieberman and Edmund Crelin, this would have caused the larynx to open into the pharynx higher along its path, limiting the ability of Neanderthals to make the “i”, “a”, and “u” sounds which are nearly ubiquitous in modern languages. Therefore, Liberman and Crelin argue, Neanderthals could not articulate “human speech”, and, given that everyone and their mother has a pet hypothesis for the extinction of our closest relative, this linguistic deficiency was the deciding factor in the Neanderthal downfall.
Needles to say, their hypothesis is not the final word. In a 2007 letter to the Journal of Phonetics, Louis-Jean Böe and other researchers offered an alternate interpretation of where the Neanderthal hyoid fit and what sounds the prehistoric people were capable of. The Neanderthal hyoid was not restrictively high, and even then, the researchers countered, the tongue, jaw, and lips are more important in making “i”, “a”, and “u” sounds. Neanderthals didn’t have any physical impediment to speaking like we do, although whatever they may have said to each other, and to us, is lost in time.
Humans aren’t the only creatures to have hyoids, though. The bone has a very ancient origin, modified from gill arches of fish that lived over 375 million years ago, and has been inherited by amphibians, reptiles, birds, and mammals. And in some of these lineages, different species have been adapted to use their hyoid for a very specialized function – to suck.
A few weeks ago, while I was walking through the National Museum of Natural History’s osteology hall, I stopped in my tracks to stare at the skeleton of a matamata. Its large hyoid is what grabbed my attention. The bony stirrup is what allows the matamata to feed without biting, and is part of what herpetologist Patrick Lemell and coauthors have dubbed “adaptation perfected”.
Imagine a twitchy little fish wriggling through the water in front of a matamata. The morsel is just out of range for the turtle to snatch with its jaws, but the reptile has another method. Muscles anchored to the turtle’s large hyoid bone throw down the lower jaw as skin at the side of the mouth create reptilian cheeks. The turtle makes such an effective vacuum that it doesn’t even need to bite. The fish is drawn in and swallowed whole. While I can imagine some situations in which such an ability might be advantageous – like when when presented with a pizza – I’m happier not looking like the fringed turtle. I will have to live with being imperfectly adapted.
Böe, L., Heim, J., Honda, K., Maeda, S. Badin, P. Abry, C. 2007. The vocal tract of newborn humans and Neanderthals: Acoustic capabilities and consequences for the debate on the origin of language. A reply to Liberman (2007a). Journal of Phonetics. 35: 564-581. doi: 10.1016/j.wocn.2007.06.006
Lemell, P., Beisser, C. Gumpenberger, M. Snelderwaard, P., Gemel, R. Weisgram, J. 2010. The feeding apparatus of Chelus fimbriatus (Pleurodira; Chelidae) – adaptation perfected? Amphibia-Reptilia. 31: 97-107.
Lemell, P., Lemell, C. Snelderwaard, P. Gumpenberger, M., Wocheslander, R., Weisgram, J. 2002. Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae)Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae)Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae). The Journal of Experimental Biology. 205: 1495-1506.