Hominin vocal tract reconstructions

The structure of the hominin vocal tract is an important determinant of speech and language abilities. Modern humans, with a long, round tongue, low, descended hyoid and larynx, and equally-proportioned vocal tract, are able to produce quantal speech sounds - such as [i], [a], and [u] - that improve speech perception and speed up the rate at which data can be transmitted. I have reconstructed the sizes and shapes of hominin vocal tracts by calculating the vocal tract proportions that could fit into reconstructions of the head and neck. Results from this research are in review at Journal of Human Evolution. I am currently collecting magnetic resonance imaging (MRI) and acoustic data on living humans to improve hominin SVT reconstructions. Click on [this link] to see details of this project, and [this link] to find out what the vocal tracts of different hominins looked like (coming soon).

Speech synthesis

These vocal tract reconstructions can be used to determine the types of vocalizations that Neanderthals and other pre-modern humans would have been able to produce. I am conducting this research in collaboration with Philip Lieberman from Brown University. We found that Neanderthals and the earliest pre-modern H. sapiens could not have produced quantal speech. We were also able to synthesize a Neanderthal [i]-like vowel from estimated formant frequencies using a Klatt synthesizer, thereby producing, for the first time, a Neanderthal vocalization. You can hear the Neanderthal [i]-like vowel [here], and an [i] synthesized using a modern human 1:1 SVT for comparison [here]. We are working on synthesizing additional Neanderthal speech sounds in order to create phonemes and simple phoneme combinations.

Constraints on primate skull shape

In my doctoral dissertation, I investigated hypothesized constraints on primate craniofacial growth and architecture. Many such constraints on skull form had been proposed by orthodontists and craniologists using 2-D x-rays. I found that a few such constraints limit skull form in primates. For example, the posterior maxillary plane at the junction between the sphenoid and frontal bone at the back of the midface maintains a 90 degree angle with the axis of the orbits (see pdf here), and the angle of the cribriform plate maintains a 90 degree angle with the profile of the anterior midface. In general, scaling relationships between the brain and underlying cranial base and face limit primate skull form, and have important down-the-line consequences for tooth development and eruption and size and shape of the speech apparatus (see above).

Basicranial flexion and length

One of my abiding interests is basicranial flexion. The human skull base is "flexed" around the pituitary fossa, a state often attributed to the development and evolution of a large brain within a limited space. All recent studies support this "spatial packing" or "brain packaging" hypothesis, including this paper. Previous researchers have noted that basicranial length scales with body mass with stronger negative allometry than brain mass scales with body mass, suggesting that human basicranial flexion may be related to factors not necessarily having anything to do with the development of a large brain. In collaboration with David Strait from University at Albany, I am testing this hypothesis by analyzing the scaling relationships between specific segments of the cranial base and adjacent soft tissues such as the eyeballs and surrounding parts of the brain.

Life history, growth and development

One of the costs of having a large, energetically-expensive brain is that it is costly to grow, particularly early during ontogeny. Humans remain small during childhood and delay somatic growth until an adolescent growth spurt, freeing up energy early during development. I am part of a research group that is re-interpreting growth and development in the ~1.55-million-year-old H. erectus juvenile KNM-WT 15000. We used alternate models of juvenile growth to estimate a revised adult stature of 5'4" for this specimen (see pdf here). I am also working on several aspects of Neanderthal life history in collaboration with Amy Lupo from University of Minnesota. Many of my master's students (here, here, here, here) have worked on hominin growth and development.

Taxonomy and phylogeny

I am interested in several issues related to hominin taxonomy and phylogeny. On the theoretical side, I am interested in how hominin paleontologists use similarity to test a commonly-accepted null hypothesis that two or more specimens belong to the same species. In collaboration with Tom DiVito from Florida Atlantic University, I showed that emphasis on similarity without recognition of phylogenetic history leads to taxonomic errors. I am also worried that researchers working on hominin phylogeny unnecessarily limit themselves to craniodental remains, a small subset of all the available skeletal data. Emphasis on one or just a few data partititions in taxonomic or phylogenetic analyses decreases the probability of finding the type of similarity - such as autapomorphy or synapomorphy - that would be useful at a particular level of analysis. On the practical side, I am very interested in the taxonomic and phylogenetic relationships of Neanderthals and other middle and late Pleistocene hominins. I have recently submitted a paper on the taxonomic position of the BOU-VP-16/1 Herto cranium to Journal of Human Evolution.