Dan Greene


Daniel R. Green
Graduate Student

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I study the evolution of human behavior by looking into how our ancestors grew from childhood into maturity, and by then following changes in their diet or health during that period of growth. Reconstructing the history of an individual’s development into adulthood is made possible by examining their teeth under microscopes: like bones or trees, teeth grow during childhood by adding on small layers of tissue at regular intervals. This kind of tooth growth stops after an individual reaches maturity, but we can still study the process of childhood growth even after death, fossilization, and re-discovery by paleontologists millions of years later. A microscopic analysis of teeth can reveal major differences between modern humans and our ancient ancestors, including the speed of growth, the length of childhood, and even the timing of certain stressful situations, including disease, starvation or injury.

We can also learn things about our ancestors by examining the chemical composition of their teeth. Teeth are made of the strongest biological materials on earth, and are incredibly resistant to change even when buried in the ground for long periods of time. As layers of enamel are deposited during an individual’s childhood, the chemistry of their food and of their environment becomes embedded in their teeth. Millions of years later, by examining the chemical composition of teeth and specifically looking at the ratios of certain atomic isotopes, we can begin to reconstruct the environments and diets of our ancestors.

I work with scientists Tanya Smith and Noreen Tuross to explore how dental microstructure and isotopic chemistry can be combined in an effort to better understand the past. Advances in histological and chemical sciences make this collaborative work possible at Harvard and at many other institutions around the world.