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Biomedical subjects

S M Case

Publications and source records attributed to S M Case.

42 records · Page 3Linked to original sources
PubMed1978

Frog perspective on the morphological difference between humans and chimpanzees.

The body shapes of humans and chimpanzees were compared quantitatively by criteria chosen for their capacity to discriminate well among the body shapes of frogs. By these criteria, the difference in body shape between humans and chimpanzees was found to be greater than that between the most dissimilar pairs of frogs examined--that is, frogs classified in separate taxonomic suborders. Even though the morphological diffference between the two primates is large by frog standards, the biochemical differences between the structural genes of these two species are small. The results of this study give quantitative support to the proposal that morphological evolution and biochemical evolution in structural genes can proceed at independent rates.

Animals↗
PubMed1977

Rapid speciation and chromosomal evolution in mammals.

To test the hypothesis that population subdivision into small demes promotes both rapid speciation and evolutionary changes in gene arrangement by inbreeding and drift, we estimated rates of speciation and rates of chromosomal evolution in 225 genera of vertebrates. Rates of speciation were estimated by considering the number of living species in each genus and the fossil record of each genus as well as information about extinction rates. Speciation rate was strongly correlated with rate of chromosomal evolution and average rates of speciation in lower vertebrate genera were one-fifth those in mammalian genera. Genera with high karyotypic diversity and rapid speciation rates may generally have small effective population size (Ne), whereas large Ne values may be associated with karyotypically uniform genera and slow rates of speciation. Speciation and chromosomal evolution seem fastest in those genera with species organized into clans or harems (e.g., some primates and horses) or with limited adult vagility and juvenile dispersal, patchy distribution, and strong individual territoriality (e.g., some rodents). This is consistent with the above hypothesis regarding the evolutionary importance of demes.

Animals↗
PubMed1975

Social structuring of mammalian populations and rate of chromosomal evolution.

To test the hypothesis that the evolution of organisms is dependent to a large degree on gene rearrangement, we devised a way of estimating rates of evolutionary change in karyotype. This non-biochemical method is based on consideration of chromosomal variability within taxonomic groups having a fossil record. The results show that chromosomal evolution has been faster in placental mammals than in other vertebrates or molluscs. This finding is consistent with published evidence that placentals have also been evolving unusually fast in anatomy and way of life. However, the structural genes of placentals seem not to have experienced accelerated evolution. Possibly, therefore, anatomical evolution may be facilitated by gene rearrangement. To explain how placentals achieved this rate of chromosomal evolution, we consider the process by which a new gene arrangement becomes fixed and spreads. The structure and dynamics of placental populations may be especially favorable for this process. The key factor involved seems to be the type of social behavior which produces small effective population sizes and inbreeding. As Bush points out elsewhere, such social structuring of populations may promote rapid fixation of gene rearrangements and rapid speciation.

Animals↗
PubMedDate not supplied

Examining the influence of gender on medical students' decision making.

Gender bias, described among practicing physicians, has rarely been examined in medical students. The current study examined the influence of gender bias on medical students' clinical decision making. We experimentally manipulated patient gender in 27 written clinical vignettes embedded in the United States Medical Licensing Examination (USMLE) Step 2 examination (a multiple-choice test of clinical decision making). Female and male patient versions of selected test cases were created within three categories: (1) diseases with previously established evidence of gender bias in the diagnosis or management of the disease, (2) diseases with a higher prevalence in a specific gender, and (3) diseases with similar prevalence in both genders and without evidence of gender bias in the literature. Among the 3059 students who wrote the USMLE Step 2 examination in August 1998, there were small but significant differences in performance on the 12 gender bias cases. Students performed worse for the female patient version of the cases compared with the male patient version of the cases (mean of 55.8% correct for female cases compared with 57.7% correct for male cases) (p < 0. 01). Our data suggest that students were variably influenced by gender bias in their investigation and management of patients in a written test of clinical decision making.

Adult↗