What did you think of the reading?
Analyzing chapters scrutinizing head formation, body plans, and nasal receptors may not sound extremely captivating, but with Shubin’s intriguing narration and straightforward explanations, I can definitely say otherwise. In the chapters I read over the past two weeks, I recognized some connections between species, particularly in their growth and development. These concepts not only reinforced what I learned in Embryology class (as I had noticed in previous chapters) but also tied in Honors Biology topics as well, from homeobox genes in flies to the tube-within-a-tube body plan.
What did you learn from the reading?
In describing the anatomy of the head, Shubin first depicts the complexity of human cranial nerves, then goes back in time to describe the evolution from simpler structures (as found in shark heads) to more modern, intricate structures found in mammals. Detailed diagrams highlighted the similarities between human and shark embryos, specifically in gill arches. They also served to show the development from human embryo to adult heads, as well as the correlation between adult shark and adult human cranial nerves.
Recognizing Embryology concepts regarding developmental body plans, the next chapter discussed the three layers of the developing embryo, the first few weeks after fertilization, and the tube-within-a-tube body plan. In addition to these familiar concepts, some that were new to me included the Organizer gene, which controlled which cells grew or died, and embryo experiments with this gene. To think that the right piece of the embryo, so vital to the developing egg can be manipulated onto another to make twins greatly fascinated me. The reintroduction of Hox genes in flies enlightened me as well, as to its universal nature (since it’s found in every animal with a body).
Not only was the development of bodies an important area of study, but the origin and evolution of the first primitive bodies were essential ideas as well. A random clump of cells does not necessarily form a tissue or body of its own; connections must be present between cells in order to regulate a more complex being, versus just a “blob”. The PreCambrian era was when single celled organisms just existed on their own; it took billions of years for the first body to develop. When this happened, the connections that held the cells together were discovered. Materials such as collagen, hydroxyapatite, cartilage, and proteoglycans served as communication between cells, as well as protection for our bones and joints. Along with the increase of oxygen in the atmosphere, bodies made their first appearance on Earth.
What questions do you still have?
A timeline in Chapter 7 showed a large gap between the beginning of life in single-celled organisms and the origin of bodies. Shubin extensively elaborated upon the need for connections between cells, such as collagen, in order for complex organisms to arise. Can it be possible that this gap resulted because there were no such connections between cells until more recent times?