YIF: Chapter 5

            This chapter was in some ways irrelevant to evolution. It took a little while for the author to tie what he was saying into the evolution of human. What he was mainly talking about was the head of mammals, fish, worms, and humans. What was special and what he said that they all have in common, yes even the headless worms, was that they all had something called the four gill arches. Each of the four categories of animals that I listed not long ago all have these arches and they look similar to each other when each of these animals is an embryo. It is when they develop further along into the stages of their embryo that they separate and look different from each other and each of the gills forms into something different. The author didn’t relate the four gill arches to the evolution of humans until he mentioned that the essence of our heads goes back to worms, such as the Amphioxus, who didn’t even have heads, and this is because these worms have the same gill arches, but when they develop they form separate organs that humans do and it is believed that these headless worms are part of the origin of the arches that we have. The most interesting part of this chapter was when the author said that “we can manipulate the identity of the gill arches almost at will, by changing of the gills inside.” (Shubin 94). This fascinated me more so than other parts of this chapter because it kind of reminded me of the ZPAs that we heard about a few chapters ago, in that we can manipulate the genes to change the embryo when it fully develops. In the book the author used the example of manipulating the gill arches of frogs by turning off some of the genes in the gill arches. The outcome of this was that the frog ended up with two jaws. That is simply interesting, however this does have much to do with evolution, and it only deals with the biology of embryos. This chapter has connections with two Big Ideas in biology, one being biological systems interacts, and these systems and their interactions possess complex properties, and the process of evolution drives the diversity and unity of life. The first idea makes a connection with this chapter because of the insane complexity of the four gill arches and how they develop into something so specialized and they interact with each other to make the organism better functioning. The second Big Idea makes a connection with this chapter because of the idea that the headless worms that existed millions of years ago share the same gill arches that several different animals, ranging from sharks to humans, have the same arches, but they develop into organs with different functions. This idea means that the diversity of the mammals can be unified by using the perspective of this one evolutionary aspect.