Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins

A modern human-like sequence of dental development, as a proxy for the pace of life history, is regarded as one of the diagnostic hallmarks of our own genus Homo(1-3). Brain size, age at first reproduction, lifespan and other life-history traits correlate tightly with dental development(4-6). Here w e report differences in enamel growth that show the earliest fossils attrib uted to Homo do not resemble modern humans in their development. We used da ily incremental markings in enamel to calculate rates of enamel formation i n 13 fossil hominins and identified differences in this key determinant of tooth formation time. Neither australopiths nor fossils currently attribute d to early Homo shared the slow trajectory of enamel growth typical of mode rn humans; rather, both resembled modern and fossil African apes. We then r econstructed tooth formation times in australopiths, in the similar to1.5-M yr-old Homo erectus skeleton from Nariokotome, Kenya(7), and in another Hom o erectus specimen, Sangiran S7-37 from Java(8). These times were shorter t han those in modern humans. It therefore seems likely that truly modern den tal development emerged relatively late in human evolution.