The relationship between H. habilis and other hominins is central to debates over the origin and early evolution of our genus, Homo. A large portion of the species' fossilized remains consists of teeth, which had until now only been studied at the often worn enamel surface. Researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and international colleagues have investigated the internal morphology of H. habilis teeth for the first time. They looked at the enamel-dentine junction (EDJ), which is preserved in cases of moderate tooth wear and is known to carry a strong taxonomic signal. The researchers compared the shape and size of the EDJ in H. habilis to a large comparative hominin and ape sample, including over 900 teeth in total, from the entire mandibular and maxillary tooth rows. The team found that EDJ morphology in H. habilis is for the most part remarkably primitive, supporting the hypothesis that from a morphological point of view H. habilis has more in common with Australopithecus than later members of the genus Homo. They also found high levels of variation within H. habilis, which may be too much for a single species.