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Biomedical subjects

D Falk

Publications and source records attributed to D Falk.

36 records · Page 2Linked to original sources
PubMed1986

Evolution of cranial blood drainage in hominids: enlarged occipital/marginal sinuses and emissary foramina.

Physiological studies of cranial blood flow in humans in reclining vs. upright postures suggest that selection for bipedalism was correlated with the establishment of epigenetic adaptations for delivering blood preferentially to the vertebral plexus of veins, depending upon momentary respiratory and postural constraints. The frequencies of vascular/osteological channels used to deliver blood to the vertebral plexus of veins were determined for samples of African pongids, various taxa of fossil hominids, and extant Homo sapiens. These channels include an enlarged occipital/marginal (O/M) sinus system, multiple hypoglossal canals, and foramina that conduct emissary veins: posterior condyloid, mastoid, occipital, and parietal. The African pongid, and therefore presumably the ancestral prebipedal hominoid, condition is characterized by low frequencies of all of these routes except multiple hypoglossal canals. The earliest known bipeds (Australopithecus afarensis) and robust australopithecines are characterized by fixation of enlarged O/M sinus systems. Robust australopithecines are also characterized by apparently low frequencies of mastoid and parietal foramina, and high frequencies of multiple hypoglossal canals and posterior condyloid foramina. In gracile australopithecines and subsequently living hominids, trends towards increased frequencies of mastoid and (later) parietal emissary foramina coincide with a trend towards decreased frequencies of an enlarged O/M sinus system and multiple hypoglossal canals. These findings suggest that selection for bipedalism initially resulted in epigenetic adaptations for routes to deliver blood to the vertebral plexus including an enlarged O/M sinus system and hypoglossal canals, but that the pressures underlying these adaptations relaxed as bipedalism became established, and other routes for delivering blood to the vertebral plexus of veins were either directly or indirectly selected for, perhaps in conjunction with a changing architecture of the skull. A systematic implication of this study is that robust australopithecines are descendants of A. afarensis rather than of A. africanus.

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PubMed1986

Advanced computer graphics technology reveals cortical asymmetry in endocasts of rhesus monkeys.

Lengths of cortical sulci were measured on ten endocranial casts (endocasts) from skulls of rhesus monkeys, using advanced computer technology that permits analysis and imaging of surface morphology in three dimensions. Sulcal lengths were compared in left and right hemispheres and, contrary to earlier reports, the length of the left Sylvian fissure was found to be significantly longer than its right counterpart, as is the case for chimpanzees and humans. This asymmetry in humans is thought to be associated with asymmetrical representation of language functions in the left hemisphere and, although this report is the first to demonstrate a significantly longer left Sylvian fissure in rhesus monkeys, our results are in keeping with psychophysical evidence that suggests that Macaca is left hemisphere dominant for perception of meaningful vocalizations. We attribute the difference between our findings and previous reports to the sensitivity of the new computer technology used to collect data from endocasts.

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PubMed1985

Apples, oranges, and the lunate sulcus.

Holloway (1984) used a method of direct tape-arc measurements on chimpanzee brain casts to reject the hypothesis that the lunate sulcus is located in an anterior position in the Taung endocast. However, Holloway neglected to measure the occipital pole-lunate sulcus (OP-LS) arc directly on the Taung endocast as he did on chimpanzee brain casts (a crucial part of his methodology); instead, he determined the relative position of Taung's lunate sulcus on the basis of a calculation that confounds direct measurements and measurements from photographs. When arc OP-LS is measured directly on Taung according to Holloway's methods, the feature that has been identified as the medial end of the lunate sulcus is shown to be located within the range that Holloway determined for chimpanzees. Thus Holloway's methodology and data support rather than refute the claim that the lunate sulcus is located in a pongid-like position in australopithecines.

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PubMed1983

The Taung endocast: a reply to Holloway.

Indices of rostrality (ir, ir') are developed to assess the extent to which the medial end of the lunate sulcus (L) is rostrally positioned in photographs and figures of lateral views of primate brains and endocasts, and indices are determined for chimpanzees, SK 1585 and the Taung endocast. Ir quantifies the extent of rostrality as it has traditionally been viewed (in A-P projections) while ir' takes dorsal curvature into account. The ir of the feature that I have identified as the lunate sulcus of Taung is within one standard deviation of the mean ir for Pan and its ir' is within 1.5 standard deviations from the mean ir' for Pan. Both findings are compatible with my earlier statement that the medial end of the lunate sulcus of the Taung endocast is in a pongid-like position. Use of stereoplotting to transfer the position of L from chimpanzee endocasts and brains to australopithecine endocasts is critically assessed: Holloway stereoplotted five chimpanzee brains and then transferred their mean coordinates that describe the lunate sulcus to the Taung endocast. If stereoplotting successfully transfers the extent to which L is rostrally located, one would expect the mean L of Pan and its transferred counterpart in Taung to have identical index values of rostrality. However, the ir of the lunate sulcus that Holloway located on Taung is over two standard deviations lower than the mean ir for the five chimpanzees he stereoplotted to determine its angular coordinates, and Holloway's ir' for Taung is one standard deviation lower than the five chimpanzees' mean ir'. These discrepancies are shown to be due to shape differences, and it is concluded that stereoplotting should not be used to transfer sulci between differently shaped endocasts without correcting for these differences. I also reply to Holloway's criticisms of my use of L/H indices, palpation, techniques for sampling endocasts, and illustration of the Taung endocast. It is shown that there is room on the Taung specimen for the lateral end of L, and the pongid-like sulcal pattern of Taung is reaffirmed. Thus, we do not yet know when human-like sulcal patterns first appeared in the hominid fossil record.

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PubMed1983

Differentiation of Staphylococcus and Micrococcus spp. with the Taxo A bacitracin disk.

Taxo A bacitracin disks (BBL Microbiology Systems, Cockeysville, Md.) were evaluated as a test for differentiating staphylococci from micrococci in clinical laboratories. All staphylococci tested were resistant to the disks, with no zone of growth inhibition. Zones of growth inhibition ranging from 10.5 to 25.0 mm in diameter were observed with all micrococci except two isolates which failed to grow on the test medium. These findings were confirmed by minimal inhibitory concentrations to bacitracin. Staphylococci had minimal inhibitory concentrations significantly higher than those of micrococci, with no overlap in the ranges of values.

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PubMed1980

A reanalysis of the South African australopithecine natural endocasts.

Sulcal patterns of six previously available South African australopithecine natural endocasts are reexamined and compared to sulcal patterns of 17 human, 12 gorilla and six chimpanzee brains. In addition, a seventh natural endocast, from STS 58, is described for the first time and compared to an artificial endocast from the same specimen. Using the Taung endocast as a focal point, it is shown that sulcal patterns reproduced on natural endocasts of australopithecines appear to be pongid-like rather than human-like. Contrary to earlier descriptions, the lunate sulcus occupies a rostral position similar to that found in pongids. Since South African australopithecine brains do not appear to be reorganized along human lines at a gross external neuroanatomical level, the concept of neurological reorganization is best applied at finer neurological levels, perhaps at the level of the neuron or at a neurochemical level. Thus, future studies by comparative neuroscientists are more likely to elucidate the fine details of neurological reorganization that occurred during early human evolution than are studies by paleontologists who directly observe the australopithecine fossil record of natural endocasts.

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PubMed1979

On a new australopithecine partial endocast.

A newly discovered right parietal/temporal/frontal fragment from an australopithecine natural endocast is described and compared to other australopithecine endocasts. This specimen shows that the central sulcus was arched, rather than straight as previously believed, and reveals frontal lobe convolutions not preserved in other australopithecine endocasts.

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PubMed1978

Cerebral asymmetry in Old World monkeys.

A photogrammetric computer analysis of 88 endocasts, representing 8 genera of Old World monkeys, reveals cortical asymmetry in lengths of the Sylvian fissure, superior temporal sulcus, lateral edge of the orbit and distance separating rectus and arcuate sulci. Hypothetical expansion of left prefrontal and parietal integration cortices explains these asymmetries.

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PubMed1975

Comparative anatomy of the larynx in man and the chimpanzee: implications for language in Neanderthal.

Using the larynges of the newborn human and chimpanzee as models, Lieberman and Crelin ('71) and Lieberman, Crelin and Klatt ('72) have reconstructed the larynx of the "classic" Neanderthal La Chapelle aux Saints. The authors used their reconstructed vocal tract to generate linguistic functions which led them to conclude that Neanderthal lacked the ability to produce fully articulate human speech. In this paper, it is shown that their reconstruction of the larynx of Neanderthal is based on a placement of the hyoid bone of La Chapelle which is too high. The reconstructed hyoid bone of La Chalpelle which is too high. The reconstructed hyoid bone has been placed in a position unlike that occupied by hyoid bones of newborn humans, adult humans, stillborn chimpanzees or adult chimpanzees. In any laryngeal reconstruction, the function of swallowing must be taken into account. The ability of the reconstructed Neanderthal to swallow is discussed in light of a comparative analysis of swallowing in man and the chimpanzee. It is concluded that the statement that Neanderthal was less than fully articulate remains unsubstantiated because it rests on a questionable reconstruction of the larynx.

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PubMed1974

Functional diversity within the rudimentary locus of Drosophila melanogaster.

The rudimentary locus of Drosophila melanogaster is shown to be at least bifunctional. Mutants in different regions of the locus have either no CPSase or no ATCase activity; some mutants lack both activities. The results are discussed in correlation with the complementation and genetic map of the locus.

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PubMedDate not supplied

Hadar AL 162-28 endocast as evidence that brain enlargement preceded cortical reorganization in hominid evolution.

On the basis of a description of an endocast from Hadar early hominid AL 162-28, it has been suggested that cerebral organization towards a human pattern occurred as early as 3-4 Myr ago. I have studied a cast of the AL 162-28 calvaria and a copy of an endocast prepared from the original fossil, and report here observations regarding cranial capacity, the relationship between endocast and skull, sulcal pattern, brain shape and cranial venous sinuses. Contrary to the earlier report, all of these features appear to be consistent with an ape-like external cortical morphology in Hadar early hominids and in my view there is no evidence for expansion or reorganization of parietal/occipital regions. Cranial capacity of AL 162-28 is at least 10% and 29% smaller than respective mean capacities of subsequently living gracile and robust australopithecines, who also exhibit ape-like cortical patterns. Thus palaeoneurological evidence from the entire early hominid record suggests that the trend towards brain enlargement preceded cortical reorganization.

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PubMedDate not supplied

Heritability of brain size and surface features in rhesus macaques (Macaca mulatta).

The extent of heritability for overall brain size and regional cortical surface features such as sulcus lengths is important for demonstrating a genetic component to the observed phenotypic differences among individuals and for evaluating the potential for evolutionary change in response to selection. Although the genetics of brain size has been extensively considered, the detailed morphology of the cortical surface has not previously been subjected to genetic analysis. We estimated the heritability of brain size and cortical sulcus lengths using 438 endocranial casts taken from skeletons of rhesus macaques (Macaca mulatta) from the Cayo Santiago population. Estimates were obtained both by mother-offspring regression and symmetric-differences-squared (SDS) methods. Brain size, measured as cranial capacity, was highly and significantly heritable in this population, confirming results of previous studies with laboratory mice. Overall, cortical sulcus lengths were also heritable, with 35% of the sulci significantly heritable at the 5% level in the mother-offspring analysis. The average mother-offspring heritability estimate, 0.31, was the same as the average heritability obtained previously from a series of 56 cranial metric characters. The SDS analyses generally corresponded to the findings based on mother-offspring regressions, although the significance test appeared more conservative. Both gross and detailed morphology of the brain are heritable.

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