My research focuses on the evolution and function of the human spine. Specifically, I am interested in lumbar lordosis (curvature of the lower back). Most scholars agree that lordosis was a critical adaptation for walking and running on two legs, allowing early hominins to balance their upper bodies over their hips to maintain stability. However, estimates of lumbar curvature from fossils and modern populations around the world show that there is considerable variation between and within groups. Interpreting variations in curvature is a challenge because the biomechanical function of lordosis remains unclear.
For my dissertation, I am investigating three main issues:
1.) From a functional and evolutionary perspective, why is the lower spine curved?
2.) What factors contribute to variations in lumbar lordosis, particularly during development?
3.) What are the biomechanical benefits or costs of differing degrees of lumbar curvature?
To answer these questions, I am examining how the lower back may act as a viscoelastic system, showing both spring and damping characteristics in response to loading, such as when we walk, run, and carry loads. Using morphometrics, modeling, and experimental methods, I seek to predict and test the effects of variations in lumbar curvature on static and dynamic loading behavior in vivo.
I have been involved with several field projects in recent years, including physiological studies on human groups around the world, as well as paleoanthropological excavations of early and middle Pleistocene sites. In 2007, I joined the Koobi Fora Field School at the 1.5 million-year-old footprint site of FwJj14E in Ileret, Kenya. In 2011, I was also involved with excavations at the middle Pleistocene site of Zhoukoudian (Locality 1) near Beijing, China with a team from the Institute of Vertebrate Paleontology and Paleoanthropology. While in China in 2011, I also conducted experiments on the energetics and biomechanics of pole carrying behavior in porters from the Sichuan Basin.
Since 2012, I have been researching children (4-17 years old) in rural and urban Kalenjin populations in the Rift Valley Province, Kenya with Daniel Lieberman (Harvard), Yannis Pitsiladis (U. of Glasgow), and Paul Okutoyi (Moi University Med. School). Our team has been investigating several issues, including the barefoot versus shod running, the effects of physical activity on overall fitness and aerobic performance, and ontogenetic variations in lumbar lordosis.