When scientists discovered a 3.3 million-year-old skeleton of a child of the human lineage (hominin) in 2000, in the village of Hadar, Ethiopia, they were able to study growth and development of Australopithecus afarensis, an extinct hominin species. The team of researchers, led by Zeresenay Alemseged of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, named the fossil DIK 1-1 and nicknamed it Dikika baby after the Dikika research site. The Dikika fossil preserves much of the skull, including the jaw and teeth, which enabled scientists to study the teeth microstructures and to reconstruct the pace at which individuals of the hominin A. afarensis developed.
Researchers study fossils of juvenile hominins because those fossils illustrate the slow rate at which humans grow. One of the ways humans differ from their closest living relatives, chimpanzees and gorillas, is by their comparatively long childhood period, or period before they acquire the ability to reproduce. Researchers can study this extended childhood through the microstructures of teeth, which preserve the timing of when humans pass through stages such as weaning and tooth eruption. Scientists can reconstruct the life histories of human ancestors to learn when the evolution of the extended childhood appeared in the hominin lineage.