Showing papers on "Encephalization published in 2002"
TL;DR: The results show that human neoteny involves not only shape retardation (paedomorphosis), but also changes in relative growth velocity, and reveal that additional structural traits are rather situated in the other part of the skull.
Abstract: Heterochronic studies compare ontoge- netic trajectories of an organ in different species: here, the skulls of common chimpanzees and modern humans. A growth trajectory requires three parameters: size, shape, and ontogenetic age. One of the great advantages of the Procrustes method is the precise definition of size and shape for whole organs such as the skull. The estimated ontogenetic age (dental stages) is added to the plot to give a graphical representation to compare growth trajectories. We used the skulls of 41 Homo sapiens and 50 Pan troglodytes at various stages of growth. The Procrustes superimposition of all specimens was completed by statis- tical procedures (principal component analysis, multivar- iate regression, and discriminant function) to calculate separately size-related shape changes (allometry common to chimpanzees and humans), and interspecific shape dif- ferences (discriminant function). The results confirm the neotenic theory of the human skull (sensu Gould (1977) Ontogeny and Phylogeny, Cam- bridge: Harvard University Press; Alberch et al. (1979) Paleobiology 5:296 -317), but modify it slightly. Human growth is clearly retarded in terms of both the magnitude of changes (size-shape covariation) and shape alone (size- shape dissociation) with respect to the chimpanzees. At the end of growth, the adult skull in humans reaches an allometric shape (size-related shape) which is equivalent to that of juvenile chimpanzees with no permanent teeth, and a size which is equivalent to that of adult chimpan- zees. Our results show that human neoteny involves not only shape retardation (paedomorphosis), but also changes in relative growth velocity. Before the eruption of the first mo- lar, human growth is accelerated, and then strongly decel- erated, relative to the growth of the chimpanzee as a refer- ence. This entails a complex process, which explains why these species reach the same overall (i.e., brain face) size in adult stage. The neotenic traits seem to concern primarily the function of encephalization, but less so other parts of the skull. Our results, based on the discriminant function, reveal that additional structural traits (corresponding to the non- allometric part of the shape which is specific to humans) are rather situated in the other part of the skull. They mainly concern the equilibrium of the head related to bipedalism, and the respiratory and masticatory functions. Thus, the reduced prognathism, the flexed cranial base (forward posi- tion of the foramen magnum which is brought closer to the palate), the reduced anterior portion of the face, the reduced glabella, and the prominent nose mainly correspond to func- tional innovations which have nothing to do with a neotenic process in human evolution. The statistical analysis used here gives us the possibility to point out that some traits, which have been classically described as paedomorphic be- cause they superficially resemble juvenile traits, are in real- ity independent of growth. Am J Phys Anthropol 118:50-62, 2002. © 2002 Wiley-Liss, Inc.
139 citations
TL;DR: Results suggest that the most accurate means for quantifying the encephalization of humans and other adult primate species requires the use of Lapicque's universal exponent of 0.28 in Snell's equation of simple allometry.
58 citations
TL;DR: The present paper outlines how one might begin to construct a theory of evolutionary changes in brain function, according to which behavioral functions generally shift from "lower" to "higher" brain regions as one ascends the so-called phylogenetic scale.
37 citations
1 Jan 2002
TL;DR: The human gut is the only organ which shows a reduced size and energy demand relative to that expected for the authors' body size, however a reduced gut size is only possible with a shift to a ‘high quality’ diet.
Abstract: With the emergence of the various species of the genus Homo at least 2–3 million years ago, a rapid increase in brain mass relative to body mass (encephalization) occurred (1). As humans fit the Kleiber equation for predictive value of resting metabolic rate (RMR) relative to body size (2), a reduction in the size and energy demand of another organ was necessary. The human gut is the only organ which shows a reduced size and energy demand relative to that expected for our body size (3). However a reduced gut size is only possible with a shift to a ‘high quality’ diet.