Knowledge about the evolution of life history in hominins is one of the most important challenges in palaeoanthropology. A list of traits, such as a relatively short birth interval, helpless newborns, a high rate of postnatal brain growth, extended period of offspring dependency, intense maternal and paternal care, prolonged period of maturation, marked adolescent growth spurt, and delayed reproduction cycles characterize our unique life strategy, differentiating us from living great apes. The questions of how, when, and in which chronological order these traits were acquired have attracted the attention of paleoanthropologists throughout the twentieth century (Bolk, 1926; Dart, 1948; Etkin, 1954; Isaac, 1978; Keith, 1949; Lancaster, 1978; Le Gros Clark, 1947; Lovejoy, 1981; Mann, 1968; Montagu, 1961; Washburn, 1960).
In the last 20 years there has been an intense debate concerning whether early hominins had an ape- or human-like life-history pattern. Information obtained from the study of tooth development and eruption patterns, as well as the dental tissues (especially enamel) has been used as the basic argument to defend the opposing views in this debate (Bromage & Dean, 1985; Conroy & Vannier, 1987; Mann, 1975, 1988; Mann et al., 1987, 1990a, 1990b, 1991; Simpson et al., 1990; Smith, 1986, 1994). Recently, the general consensus is that a short life history characterized Australopithecus, Paranthropus, and early Homo. The subsequent evolution of the genus Homo included an overall lengthening of development, as well as the appearance of new life stages (Bogin & Smith, 1996).