Endocranial volume and brain growth in immature Neandertals

Abstract

Microstructural studies have suggested that an extended period of growth was absent in representatives of Homo erectus, and that Neandertals reached adulthood significantly more rapidly than modern humans.In addition to general rate of growth, a prolonged postnatal period of brain development allows humans to develop complex cognitive and social skills.Conditions in brain growth similar to those observed in extant humans were not established in the first representatives of Homo erectus.To assess the degree of secondary altriciality reached by Neandertals, we examined the most complete skulls available for immature Neandertal specimens.The endocranial volumes were evaluated by using equations based on external cranial measurements.The proportional endocranial volumes (PEV) of these fossils were compared to the PEV of known age modern children from Western Europe and to a developmental series of Pan troglodytes.We present an estimation of the cranial capacity of Krapina 1.Although Neandertal children are close to the modern variation, the position of the youngest specimens in the upper range of variation led us to propose that Neandertals may have displayed a slightly more primitive pattern with respect to the speed of brain growth. GENERAL RATE OF GROWTHH umans differ from other primates in their development pattern and particularly in the marked lengthening of their growth processes.These differences have a number of implications, not only in biological terms, but also in terms of social organization, mating strategies, and an extension of the learning period.However, to date, the precise point when a modern growth pattern was established during the course of human evolution still remains obscure.Dental and somatic growth are highly correlated across the primate order (1-4).Thus, advances on the issue of differences in life history between hominin species result primarily from an emphasis placed on dental development and, more specifically, microstructural studies.Recent reassessments of the life history in extinct hominins based on dental studies suggest significant differences in the timing of individual development (5, 6).Based on the analysis of the enamel apposition rate, Dean et al. (5) established that an enlarged period of growth was absent in representatives of Australopithecus and early Homo, and specifically Homo erectus.These species more closely align with extant apes than with recent humans.

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