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- All Subjects: Embryology
Description
In 1997, developmental biologist Michael Richardson compared his research team's embryo photographs to Ernst Haeckel's 1874 embryo drawings and called Haeckel's work noncredible.Science soon published <“>Haeckel's Embryos: Fraud Rediscovered,<”> and Richardson's comments further reinvigorated criticism of Haeckel by others with articles in The American Biology Teacher, <“>Haeckel's Embryos and Evolution: Setting the Record Straight <”> and the New York Times, <“>Biology Text Illustrations more Fiction than Fact.<”> Meanwhile, others emphatically stated that the goal of comparative embryology was not to resurrect Haeckel's work. At the center of the controversy was Haeckel's no-longer-accepted idea of recapitulation. Haeckel believed that the development of an embryo revealed the adult stages of the organism's ancestors. Haeckel represented this idea with drawings of vertebrate embryos at similar developmental stages. This is Haeckel's embryo grid, the most common of all illustrations in biology textbooks. Yet, Haeckel's embryo grids are much more complex than any textbook explanation. I examined 240 high school biology textbooks, from 1907 to 2010, for embryo grids. I coded and categorized the grids according to accompanying discussion of (a) embryonic similarities (b) recapitulation, (c) common ancestors, and (d) evolution. The textbooks show changing narratives. Embryo grids gained prominence in the 1940s, and the trend continued until criticisms of Haeckel reemerged in the late 1990s, resulting in (a) grids with fewer organisms and developmental stages or (b) no grid at all. Discussion about embryos and evolution dropped significantly.
ContributorsWellner, Karen L (Author) / Maienschein, Jane (Thesis advisor) / Ellison, Karin D. (Committee member) / Creath, Richard (Committee member) / Robert, Jason S. (Committee member) / Laubichler, Manfred D. (Committee member) / Arizona State University (Publisher)
Created2014
Description
The development of the vertebrate musculoskeletal system is a highly dynamic process, requiring tight control of the specification and patterning of myogenic, chondrogenic and tenogenic cell types. Development of the diverse musculoskeletal lineages from a common embryonic origin in the paraxial mesoderm indicates the presence of a regulatory network of transcription factors that direct lineage decisions. The basic helix-loop-helix transcription factor, PARAXIS, is expressed in the paraxial mesoderm during vertebrate somitogenesis, where it has been shown to play a critical role in the mesenchymal-to-epithelial transition associated with somitogenesis, and the development of the hypaxial skeletal musculature and axial skeleton. In an effort to elucidate the underlying genetic mechanism by which PARAXIS regulates the musculoskeletal system, I performed a microarray-based, genome-wide analysis comparing transcription levels in the somites of Paraxis-/- and Paraxis+/+ embryos. This study revealed targets of PARAXIS involved in multiple aspects of mesenchymal-to-epithelial transition, including Fap and Dmrt2, which modulate cell-extracellular matrix adhesion. Additionally, in the epaxial dermomyotome, PARAXIS activates the expression of the integrin subunits a4 and a6, which bind fibronectin and laminin, respectively, and help organize the patterning of trunk skeletal muscle. Finally, PARAXIS activates the expression of genes required for the epithelial-to-mesenchymal transition and migration of hypaxial myoblasts into the limb, including Lbx1 and Met. Together, these data point to a role for PARAXIS in the morphogenetic control of musculoskeletal patterning.
ContributorsRowton, Megan (Author) / Rawls, Alan (Thesis advisor) / Wilson-Rawls, Jeanne (Committee member) / Kusumi, Kenro (Committee member) / Gadau, Juergen (Committee member) / Arizona State University (Publisher)
Created2013
Description
Biology textbooks are everybody's business. In accepting the view that texts are created with specific social goals in mind, I examined 127 twentieth-century high school biology textbooks for representations of animal development. Paragraphs and visual representations were coded and placed in one of four scientific literacy categories: descriptive, investigative, nature of science, and human embryos, technology, and society (HETS). I then interpreted how embryos and fetuses have been socially constructed for students. I also examined the use of Haeckel's embryo drawings to support recapitulation and evolutionary theory. Textbooks revealed that publication of Haeckel's drawings was influenced by evolutionists and anti-evolutionists in the 1930s, 1960s, and the 1990s. Haeckel's embryos continue to persist in textbooks because they "safely" illustrate similarities between embryos and are rarely discussed in enough detail to understand comparative embryology's role in the support of evolution. Certain events coincided with changes in how embryos were presented: (a) the growth of the American Medical Association (AMA) and an increase in birth rates (1950s); (b) the Biological Sciences Curriculum Study (BSCS) and public acceptance of birth control methods (1960s); (c) Roe vs. Wade (1973); (d) in vitro fertilization and Lennart Nilsson's photographs (1970s); (e) prenatal technology and fetocentrism (1980s); and (f) genetic engineering and Science-Technology-Society (STS) curriculum (1980s and 1990s). By the end of the twentieth century, changing conceptions, research practices, and technologies all combined to transform the nature of biological development. Human embryos went from a highly descriptive, static, and private object to that of sometimes contentious public figure. I contend that an ignored source for helping move embryos into the public realm is schoolbooks. Throughout the 1900s, authors and publishers accomplished this by placing biology textbook embryos and fetuses in several different contexts--biological, technological, experimental, moral, social, and legal.
ContributorsWellner, Karen L (Author) / Maienschein, Jane (Thesis advisor) / Ellison, Karin D. (Committee member) / Robert, Jason S. (Committee member) / Arizona State University (Publisher)
Created2010