Humans, uniquely among anthropoids, have a prolonged life history. Extended life history periods are
undoubtedly important in cognitive development and the learning of language. Dental development has been shown
to be a good proxy for the pace of life history, and recent studies of dental histology have shown that brain size, age
at first reproduction, lifespan, and other traits correlate tightly with tooth development.
Humans, like other calcifying organisms, do so with a daily rhythm. Daily increments of enamel formation
can be counted in sections of teeth to calculate rates of enamel formation. This is even possible for extinct species.
Australopithecus species, putative human ancestors, have previously been shown not to have a human-like slow
growth trajectory, but rather show maturation rates like those of African great apes. Very recent work (Dean et al.,
2001, Nature 414:628) also shows that early Homo specimens also had fast growth rates. Two Homo erectus
specimens, one from Java and the other from East Africa, also developed like African great apes, despite this
species having a post cranial skeleton very similar in morphology and stature to those of modern humans.
One neandertal tooth was examined and this individual's enamel formation rate did fall within the modern human range.
We can speculate that the unique slow development of humans evolved before the neandertal-human split
(~500,000 years ago). This can be tested by looking at enamel formation rates in hominid specimens that are from
time periods earlier than the neandertal examined, but after those early hominids examined to date.
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