This study will use both bony and histological morphology of the nose (nasopharynx) to examine a comparative sample of modern primates and apply that study to answering climatic adaptational questions about Neandertals and Homo heidelbergensis. All methods used to analyze the specimens will be combined to create a three-dimensional map of the nasopharynx. By studying interaction of its hard and soft tissue components, a more robust model of its functional morphology may be derived. Data on normal growth of nasopharyngeal boundaries holds clinical importance with regard to URT diseases, which are the most common pediatric clinical conditions. This project provides previously unavailable data on the normal growth and functional morphologic relationships of nasopharyngeal boundaries, which are directly relevant to URT disease etiology.
The nasopharynx comprises a vital portion of the upper respiratory tract. Yet, patterns of morphologic change in this region over human evolution remains poorly understood. This study tests the hypothesis that the bony nasopharyngeal boundaries share a functional relationship with other units of the craniofacial skeleton. As an upper respiratory tract (URT) component, the nasopharyngeal boundaries may be subject to patterns of climatic stress and adaptation. It will thus be tested whether climatic adaptations are present in primate species inhabiting cold, dry environments. To test this hypothesis, CT imaging of nasopharyngeal boundaries will be performed on postmortem samples of macaque monkeys that died of natural causes (Macaca mulatta, Macaca fascicularis) from warm and cold climates. Those from colder environments are expected to exhibit greater nasopharyngal surface area-to-volume ratio, which would increase contact between airflow and nasopharyngeal epithelia for more efficient warming and humidification. Finally, fossil specimens attributed to Neanderthals (from cold, dry climates) and Homo heidelbergensis will undergo Generalized Procrustes Analysis (GPA) of URT landmark coordinate data for comparison with geographically diverse modern human crania. The relationship between nasopharyngeal morphology and histology will also be evaluated via light microscopy of a diverse primate sample.
As a Doctoral Dissertation Research Improvement award, it will provide support to enable a promising student to establish a strong independent research career.
The nasopharynx is a centrally located region, bounded by the nasal cavity, soft palate, basicranium, pharyngeal constrictor muscles, and cartilaginous auditory (Eustachian) tube. It is integral to a wide range of physiological functions including nasal respiration, ventilation and equilibration of air pressure within the middle ear, resonation during speech, and the sensation of flavor. As such, many clinical studies have been performed on the function of normal and diseased nasopharynges. However, few have focused exclusively on this area within the contexts of comparative development, functional morphology, or human evolution. This study aims to contribute to understanding of this crucial complex of structures. A multimodal analysis of the nasoptharynx and its boundaries was performed so that aspects of its osteology, histology, developmental plasticity, and morphology among fossil hominins may be assessed. These represent four separate analyses, each with its own hypotheses. Hypothesis 1 tested for a relationship between nasopharyngeal width and facial length, Hypothesis 2 tested for a relationship between external basicranial flexion and nasopharyngeal height and depth (in the anteroposterior dimension), and Hypothesis 3 tested whether human infants and young children exhibit cartilaginous Eustachian tubes that are relatively shorter and more horizontally oriented than the adult condition. Humans were used as models of extreme orthognathy (facial shortening) while Papio was used as an example of extreme prognathism (facial elongation). Samples were age-graded into developmental series via dental eruption ranging from edentulous newborns (Stage 1) to adults (fully erupted third maxillary molars). Result indicated: 1: Humans, the most orthognathic primates, exhibited wider nasopharynges than all other genera, lying almost completely outside of the ranges of other genera in several measures of nasopharyngeal width. 2: Basicranially flexed human adults exhibit the tall, narrow nasopharynges that are anteroposteriorly shallow when compared to newborns, which exhibit non-flexed basicrania and nasopharynges that are vertically short and anteroposteriorly longer. 3: The Eustachian tube morphology of infants is indeed more horizontal and short when compared to older children and adults. These differences correspond with ages of peak incidence of otitis media (middle ear disease). Functioning partly as a respiratory space, the nasopharynx may also aid the nasal cavity in warming and humidifying inspiratory air before it reaches the lungs. It was hypothesized that the nasopharynx was only able to warm and humidify postnasal air via cells on its bony, non-contractile surfaces as these have long been described as the only suitable substrates for respiratory epithelium as found within the nasal cavity. In testing this functional relationship, histological analysis was performed on a diverse primate sample. Resulting microscopic slides were examined via light microscopy for the presence of submucosal blood vessels, mucous cells, and serous cells, which are necessary for warming and humidifying respiratory air. Results indicated that all of these microstructures were present on all of the nasopharyngeal surfaces, rather than being restricted to non-conctractile bony surfaces. As the previous two analyses in this dissertation have focused on hard and soft tissue anatomy, a hypothesis regarding the growth of overall nasopharyngeal dimensions (including both hard and soft tissue components) was tested. It was hypothesized that populations of conspecifics raised in cold and warm outdoor colonies would exhibit disparate developmental trajectories within the upper respiratory tract, resulting in differences between both groups of adults. Two groups of adult male Rhesus monkey raised in Oregon (cold climate) and California (warm climate) outdoor colonies for the entirety of their lives were used in this study. CT imaging was used to measure nasopharyngeal surface area and volume and to collect landmark coordinate data from the entire upper respiratory tract. Oregon individuals exhibited larger overall upper respiratory tract proportions and markedly smaller body mass than the California individuals. The hypothesis is here supported. Finally, a three-dimensonal geometric morphometric analysis of fossil crania representing Neanderthals (Gibraltar Forbes’ Quarry 1, Monte Circeo 1, Saccopastore 1) and mid-Pleistocene humans from Europe (Atapuerca 5, Petralona 1, Steinheim 1) and Africa (Kabwe 1) was performed. Two hypotheses were tested: 1) Neanderthals exhibit tall, narrow nasopharynges as a respiratory adaptation to increase surface area relative-to-volume; 2) Neanderthals exhibit long, horizontally oriented Eustachian tubes relative to modern human adults. Scaled sets of landmark coordinate data were used to derive linear distances and angular measures. These led to the rejection of Hypothesis 1 as the Kabwe cranium, representing a tropical climate, expressed a relatively taller and narrower nasopharygx than Neanderthals. However, Hypothesis 2 was accepted as Neanderthals exhibited longer, more horizontal cartilaginous Eustachian tubes. These data suggest that Neanderthals possessed a Eustachian tube morphology and physiology distinct from modern humans, which may have impacted their susceptibility to middle ear disease.These results represent the first available data on Neanderthal Eustachian tube morphology and warrant further investigation into the development and physiological importance of these potential species-level differences.
