From the paper:
We find that the modern human pattern of brain development is derived compared to Neanderthals. The pattern of endocranial shape changes between age groups 2 and 6 is similar among modern humans, Neanderthals and chimpanzees [7]. Neanderthals achieved endocranial volumes comparable to modern humans following this presumably ancestral pattern of development. Our results therefore provide an ontogenetic dimension to the findings of Bruner and colleagues [2]. This challenges the view that all morphological characteristics separating modern humans from Neanderthals are already established at the time of birth. However, our results are not incompatible with the findings reported by Ponce de León and colleagues [3,4,5]: when measurements of the face and neurocranium are analyzed together, the human and Neanderthal trajectories appear to be roughly parallel [3,4] because at the time of birth the face of a Neanderthal is already larger than that of a modern human (Figure 1A).Related: Anatomically modern humans
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The development of cognitive abilities during individual growth is linked to the maturation of the underlying neural circuitry: in humans, major internal brain reorganization has been documented until adolescence, and even subtle alterations of pre- and perinatal brain development have been linked to changes of the neural wiring pattern that affect behavior and cognition [9]. The uniquely modern human pattern of early brain development is particularly interesting in the light of the recent breakthroughs in the Neanderthal genome project [10], which identified genes relevant to cognition that are derived in living humans. We speculate that a shift away from the ancestral pattern of brain development occurring in early Homo sapiens underlies brain reorganization and that the associated cognitive differences made this growth pattern a target for positive selection in modern humans.
Current Biology, Volume 20, Issue 21, R921-R922, 9 November 2010 doi:10.1016/j.cub.2010.10.018
Brain development after birth differs between Neanderthals and modern humans
Philipp Gunz et al.
Neanderthals had brain sizes comparable to modern humans, but their brain cases were elongated and not globular as in Homo sapiens[1,2]. It has, therefore, been suggested that modern humans and Neanderthals reached large brain sizes along different evolutionary pathways [2]. Here, we assess when during development these adult differences emerge. This is critical for understanding whether differences in the pattern of brain development might underlie potential cognitive differences between these two closely related groups. Previous comparisons of Neanderthal and modern human cranial development have shown that many morphological characteristics separating these two groups are already established at the time of birth [3,4,5], and that the subsequent developmental patterns of the face are similar, though not identical [6]. Here, we show that a globularization phase seen in the neurocranial development of modern humans after birth is absent from Neanderthals.
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This recalls some of the writings of John Hawks in his blog about the height of Homo Erectus.
ReplyDeleteA lot of the high end estimates are based on the assumption that juveniles have a lot more growth ahead of them, rather than on finds of individuals who were actually that tall. But, the newer research seems to indicate that instead, the full maturity height is reached earlier in the developmental life cycle.
IIRC, Pygmy height patterns are similar, with short stature having more to do with an earlier end to stature growth than with scaled differences along a similar developmental timeline.