Informative Speech On Pharyngeal Gill Arches

Pharyngeal Gill Arches
In high school I wrote a twenty minute speech for my public speaking class. The goal of the assignment was to pick a topic that we were curious about and didn’t know much about, and write an informative speech about it. I chose to write about the evidence for evolution. I learned about fossil evidence, genetic evidence, embryonic similarities, and homologous traits between seemingly unrelated species. In college, I took biology classes and learned that my speech that I wrote in high school only scratched the surface of the evidence for evolution. One example of this was that I learned that one embryonic similarity was that all chordates have pharyngeal gill slits as embryos. However, I did not know the function of these
Similar to sharks, the first gill arch forms the jaw and structures associated with the jaw such as muscles and nerves. However, “the major difference is that humans’ first arch also forms some ear bones, which we do not see in sharks” (Shubin). The two ear bones formed from the first arch are the malleus and the incus. The second arch forms the stapes and the hyoid. The third and fourth arches are the arches that are the most different between humans and sharks. These arches form the structures that allow us to talk and swallow. They form the muscles of the soft palate, the muscles of the pharynx, the larynx, the trachea, and other laryngeal cartilages (Duke Medicine). It is interesting that “the muscles and cranial nerves we use to swallow and talk move the gills in sharks and fish,” and that those same muscles are formed by that same gill arches
Inside, each PA is […] composed of mesoderm cells” (Frisdal and Trainer). In mammals, the endoderm develops into parts of the endocrine system including the thyroid, thymus, and parathyroid glands. Frisdal and Trainer explain that “The mesoderm gives rise to endothelial cells and myoblasts, the progenitors of the vasculature, and musculature.” Frisdal and Trainer also explain that the lateral part of the ectoderm forms the skin, and the medial part creates the nervous system. Each arch has these three tissues. It is interesting that these three layers are conserved throughout all chordates and that they are so similar to the three layers that make up organisms as a whole. Because scientists know what is formed by each gill arch, they are able to figure out exactly where developmental disorders originated. For example, incomplete development of the hyoid is attributed to deformity of the second arch. Another example is shown in the picture below where “both of the siblings exhibit low-set external ears [...] and hypoplasia of the mandible;” both of these deformities are due to a deformity in the first arch (Duke