Cranial capacity in hominid evolution

We present an analysis of cranial capacity of 118 hominid crania available from the literature. The crania belong to both the genusAustralopithecus andHomo and provide a clear outline of hominid cranial evolution starting at more than 3 million years ago. Beginning withA. afarensis there is a clear increase in both absolute and relative brain size with every successive time period.H.s. neandertal has an absolutely and relatively smaller brain size (1412cc, E.Q.=5.6) than fossil modernH.s. sapiens (1487cc, E.Q.=5.9). Three evolutionary models of hominid brain evolution were tested: gradualism, punctuated equilibrium, and a mixed model using both gradualism and punctuated equilibrium. Both parametric and non-parametric analyses show a clear trend toward increasing brain size withH. erectus and a possible relationship within archaicH. sapiens. An evolutionary stasis in cranial capacity could not be refuted for all other taxa. Consequently, the mixed model appears to more fully explain hominid cranial capacity evolution. However, taxonomic decisions could directly compromise the possibility of testing the evolutionary mechanisms hypothesized to be operating in hominid brain expansion.     

Cranial capacity estimates for Olduvai Hominid 7

Estimation of cranial capacity for Olduvai Hominid (OH) 7 is determined from external parietal dimensions using multiple regressions calculated from an australopithecine grade sample. Capacity estimates for OH 7 (580–600 cc) are much lower than usually claimed. While differences in reconstruction may account for the varying estimates, a regression based only on undistorted and unreconstructed values, as well as a direct comparison of dimensions with other Homo habilis specimens, supports the smaller capacity determination.     

Cranial capacity/cranial base relationships and prediction of vault form: A canonical correlation analysis

Canonical correlation analysis was used to test an hypothesized morphological relationship between vault form and cranial capacity relative to length of the chondrocranium. Ninety-five adult male Czech skulls were measured for vault form expressed as length, width and height of the brain case; the chondrocranium was represented by nasion-basion and basion-opisthion lengths. In terms of explained variation, the first and most important dimension of covariation between vault and chondrocranial variables was size. The second most significant dimension of covariation expressed the hypothesized shape relationships—i.e., overall size being equal, the shorter the chondrocranial base relative to cranial capacity, the shorter and wider the vault. Furthermore, the competing hypothesis that vault form is determined by facial length proved untenable since facial length was predictive of vault shape only when measured as prosthion-basion, a measure that incorporates basal length. When corrected for basal length, facial length is unrelated to vault form. The results are consistent with the assumption that phylogenetic and microevolutionary trends toward brachycephaly in man stem from changes in the relationship between two components of skull growth, the chondrocranial base and the brain.     

Cranial capacity estimations of the FrankfurtPan troglodytes verus collection

Cranial capacity measurements of 18 individuals (9 ♂, 9 ♀) of a total collection of 277Pan troglodytes verus skulls were taken using four different methods:- two conventional filling methods and two mathematical methods. The two mathematical analyses normally used in hominids, were for the first time specifically modified forPan. The results probably present a more accurate estimation of total cranial capacity inPan and specifically inPan troglodytes verus (352 cm³) than previously available. Sexual differences related to this trait were also measured. Regardles of the methods used,Pan troglodytes verus seems to manifest the smallest cranial capacity of all subspecies ofPan.     

Cranial capacity evolution in Homo erectus and early Homo sapiens.

This paper investigates patterns of cranial capacity evolution in Homo erectus, early Homo sapiens, and in regional subsamples of H. erectus. Specifically, models explaining evolution of cranial capacity in these taxa are evaluated with statistical techniques developed for the analysis of time series data. Regression estimates of rates of evolution in cranial capacity are also obtained. A non-parametric test for trend suggests that cranial capacity in both H. erectus and early H. sapiens may increase significantly through time. Cranial capacity in an Asian subsample of H. erectus (comprised of Chinese and Indonesian specimens) increases significantly through time. Other subsamples of H. erectus (African, Chinese, and Indonesian) do not appear to increase significantly through time. Regression results generally corroborate results of the test for trend. Spatial and temporal variation may characterize evolution of cranial capacity in H. erectus. Different patterns of cranial capacity evolution may distinguish H. erectus from early H. sapiens.     

Ruse's Darwinian meta-ethics: A critique

Michael Ruse, in Taking Darwin Seriously seeks to establish that taking Darwin seriously requires us to treat morality as subjective and naturalistic. I argue that, if morality is not objective, then we have no good reason for being moral if we can avoid detection and punishment. As a consequence, we will only continue to behave morally as long as we remain ignorant of Ruse's theory, that is, as long as the cat is not let out of the bag. Ruse offers a number of arguments to show that his theory can overcome such problems. I argue that they all fail. Ruse also argues that he can offer a naturalistic account of ethics which steps around the naturalistic fallacy and avoids the confusion of reasons with causes. His principal argument for this view is an analogy between spiritualism and morality. I argue that this analogy fails.     

Interphase chromosome order: A proposal

A model for the arrangement of chromosomes in interphase nuclei is proposed. The model assumes that interphase chromosomes have a Rabl orientation (a relic telophase arrangement). During interphase and prophase telomeres are attached to the nuclear envelope often in pairs. The association of telomeres, homologous or nonhomologous, is based on similarity of arm lengths and occurs at the time the nuclear envelope reforms. At this stage arm lengths will vary to some extent due to the amount of uncoiling etc. The sequence of chromosomes resulting from telomere-telomere pairing may vary among cells, but the number of arrangements will be restricted by arm length similarities.The ramifications of this model on melotic pairing, the constant attachment of chromosomes to some structure throughout the cell cycle, the distribution of genes within nuclei, and chromosome evolution are raised.     

Gaits of monkeys and horses: A methodological critique

In a previous paper it was shown that the traditional methodology used to analyze quadrupedal gaits is inadequate when applied to the gaits of monkeys. The traditional methods were modified for use with the monkey sample (Prost, '65). Was the modification a general improvement of the traditional approach or was it dictated by peculiarities of monkey locomotion? The traditional analysis receives its support primarily from its usefulness in handling horse gaits. If it can be shown that the modified methods improve the analysis for horses, then it can be claimed that the system is not a special case designed uniquely for use with monkeys. Motion pictures were taken of an American Saddle Bred, five-gaited horse performing several classic gaits. The films were analyzed using the modified methods developed to analyze monkey gaits. The analysis was superior to the traditional approach. All of the organizing principles which structure horse gaits were found to be identical to those which structure monkey gaits.     

Developing manufacturing control software: A survey and critique

The complexity and diversity of manufacturing software and the need to adapt this software to the frequent changes in the production requirements necessitate the use of a systematic approach to developing this software. The software life-cycle model (Royce, 1970) that consists of specifying the requirements of a software system, designing, implementing, testing, and evolving this software can be followed when developing large portions of manufacturing software. However, the presence of hardware devices in these systems and the high costs of acquiring and operating hardware devices further complicate the manufacturing software development process and require that the functionality of this software be extended to incorporate simulation and prototyping. This paper reviews recent methods for planning, scheduling, simulating, and monitoring the operation of manufacturing systems. A synopsis of the approaches to designing and implementing the real-time control software of these systems is presented. It is concluded that current methodologies support, in a very restricted sense, these planning, scheduling, and monitoring activities, and that enhanced performance can be achieved via an integrated approach.     

GDNF availability determines enteric neuron number by controlling precursor proliferation

To clarify the role of Ret signaling components in enteric nervous system (ENS) development, we evaluated ENS anatomy and intestinal contractility in mice heterozygous for Ret, GFRalpha1 and Ret ligands. These analyses demonstrate that glial cell line-derived neurotrophic factor (GDNF) and neurturin are important for different aspects of ENS development. Neurturin is essential for maintaining the size of mature enteric neurons and the extent of neuronal projections, but does not influence enteric neuron number. GDNF availability determines enteric neuron number by controlling ENS precursor proliferation. However, we were unable to find evidence of programmed cell death in the wild type ENS by immunohistochemistry for activated caspase 3. In addition, enteric neuron number is normal in Bax(-/-) and Bid(-/-) mice, suggesting that, in contrast to most of the rest of the nervous system, programmed cell death is not important for determining enteric neuron numbers. Only mild reductions in neuron size and neuronal fiber counts occur in Ret(+/-) and Gfra1(+/-) mice. All of these heterozygous mice, however, have striking problems with intestinal contractility and neurotransmitter release, demonstrating that Ret signaling is critical for both ENS structure and function.     

Reliability and validity of the physical disector method for estimating neuron number

The physical disector was proposed as an unbiased and efficient means to estimate neuron number; however, the validity and reliability of this method have been examined only infrequently. Estimates of neuron number in the dorsal root ganglia (DRG) of bullfrogs (Rana catesbeiana) were compared to nucleolar counts based on 3-dimensional reconstructions. Accuracy of disector estimates were not affected by size of the animal. Similarly, disector estimates were not systematically altered when area measurements were limited to cellular regions of the DRG versus inclusion of the entire cross-sectional area. However, the recommended protocol for applying the disector resulted in sampling errors that introduced considerable variability in repeated estimates of neuron number from a single ganglion. In addition to this lack of reliability, disector estimates were consistently lower than those obtained by means of a nucleolar counting method that was calibrated against 3-dimensional reconstructions of neuronal profiles. The systematic error of the disector method was greater when ganglia were cut parallel to the long axis of the DR than when they were cut perpendicular to this axis. Increasing the sample size beyond what was recommended increased the reliability of estimates obtained with the disector; however, the bias associated with the plane of section was not reduced. These results emphasize the need for empirical validation of methods used to estimate neuron number in the tissue to which they are to be applied. © 1996 John Wiley & Sons, Inc.