Pulling teeth from history

M olecular biology has made considerable contributions to the study of human history from the earliest days of our species, when our ancestors began to walk on the savannah, to the dawn of civilization and the more recent history of mankind. The analysis of contemporary mitochondrial DNA, for example, has told us that Homo sapiens first appeared in Africa; the sequencing of the Neanderthal genome has revealed that Homo sapiens and Homo neanderthalensis lived along each other and interbred before the latter disappeared; last year, the analysis of DNA extracted from a skeleton found under a parking lot in Leicester, UK, showed that it was the remains of King Richard III. Although the advent of next-generation sequencing and advances in bioinformatics have boosted research using ancient DNA, a major hurdle has always been the quantity and quality of the DNA itself: DNA molecules quickly degrade over time into smaller fragments, and microbial contamination makes it challenging to identify human fragments within a sample. Intriguingly, teeth have proven to be an excellent source of highquality ancient DNA, yielding insights into the evolution of the human diet, disease and immunity since the onset of agriculture some 10,000 years ago. Dental calculus has been the most complete source of historical sequence data, especially for probing oral microbiome populations. At the same time, dental pulp—the connective tissue at the centre of teeth—has been an important source of information about ancient diseases.