-Adnan Jahan
(adnanjahan@gmail.com)
Tuesday, March 22, 2011
Limbs Chapter 2
This chapter was all about how limbs and hands in particular can be a big help in following the path of evolution. Shubin starts off by talking about cadavers, and how it wasn’t until he saw the hands that he realized he was dealing with what was once a live human being. He goes on to describe how important hands are, and that they can create a greater emotional response, than one might expect. Following that, he goes onto explain how anatomist Richard Owen made the theory that all limbs, hands and feet are quite similar to each other in structure. They each follow a certain pattern that can be found in animals world wide. Describe the “pattern” to the skeleton of the human arm that was discovered by Sir Richard Owen in the mid-1800s. Relate this pattern to this idea of exceptional similarities and to Shubin's discovery.
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Sir Richard Owen was an important anatomist that was lucky enough to be alive during perhaps the most exciting phase of archaeology. In the mid 1800’s, there were still many unknown species. People like Sir Owen had the chance to be a part of the ultimate discovery. It is thanks to him that we know about dinosaurs and gorillas. But perhaps his most important discovery was the universal pattern of limbs. He first discovered a unique similarity between the structure of a human hand and a human leg. First, he noted that there is a large bone in both the upper arm and thigh. It is then followed by two bones in the forearm and leg. The two bones are followed by nine little bones in the wrist and the beginning of the foot. Finally, there are protruding rods that form the fingers and the toes. Shubin termed this pattern, “one bone, two bones, lotsa blobs, digits” (32). But Sir Owen took this discovery to another level. He did what was unheard of at the time. He compared different animals instead of looking for differences. And in doing so, he discovered “exceptional similarities” (30). All limbs of all animals follow the same one bone, two bones, lotsa blobs, digits pattern. This led to an even bigger discovery. If all limbs follow the same pattern, why are wings so different from hands? Even more than that, what differentiates the wing of a bat to that of a penguin? The reason for these differences is actually differences in the size and shape of the bones. Sir Owen went on to note even more similarities throughout the entire structure of all animals. Where Sir Owen seemingly fell short is in his belief that this was all the design of the creator.
ReplyDeleteRobbie Thomashow
(diehardcubsfan93@comcast.net)
Charles Darwin had a different point of view. He believed that the similarities were due to a common ancestor. Since not all animals have limbs, there became two clear cut possibilities. One is that limbed animals and animals without limbs evolved at the same time from different ancestors; the other possibility is that animals without limbs evolved to become limbed and they all came from one ancestor. Following Darwin’s theory of natural selection, the most likely conclusion is that animals without limbs evolved to become limbed. Natural selection is a means to insure “descent with modification” as Darwin described it (Campbell 15). In other words, a member of a species might develop a selective advantage. Those with this advantage are able to more easily obtain resources than others in the species. Since they are able to better take advantage of the resources available, they are also able to reproduce more. This means that the genes that led to the selective advantage are continued to be passed along. Meanwhile, those that lack the advantage will become less successful at mating and passing on their genes and will therefore eventually die out meaning all members of the species will have the advantage. Like Sir Owen, Darwin developed this theory based on similarities he noted in nature. He assumed that since populations produce many offspring of which only few live to reproduce, there has to be competition for resources. Furthermore, individuals share traits that are seemingly passed down from parent to offspring. Finally, species develop to fit their environment (Campbell 15). Given all of this, Darwin was able to infer that those with certain traits would be most successful allowing those traits to be passed down.
ReplyDelete-Robbie Thomashow
(diehardcubsfan93@comcast.net)
Given Darwin’s theory of Natural Selection, scientists were able to develop new ideas on the origins of life. They deduced that an original ancestor evolved into many different organisms in order to best utilize its resources. Scientists were then able to apply the same thinking to the transition of aquatic animals, to land dwelling animals. This is where Shubin factors in. Natural selection states that certain traits developed from fish that led animals to leave the water and seek resources on land. Shubin’s goal was to find the fish that left the water and became an animal. Since the process of evolution occurs gradually, this transformation occurred over a long time period. Thus, many different animals offer insight into the transformation. However, the change from fish to human is great. So then how could simple animals evolve into such complex ones? The answer to that lies at the molecular level. DNA is translated and transcribed into a protein. Each protein serves a specific function in a cell. This function determines a trait in the organism. In this way, the gene that is expressed determines the trait. Therefore a specific gene has to be responsible for the change from fish to land-dweller to human. However, research has proven that the change that led to humanity is not based on a single gene expression, but rather multiple genes being expressed. The genes that are expressed all serve one function in the organism. The group of genes comes to be by gene duplication from an ancestral gene. The products of each individual gene all perform the same function, but in differing ways. During ontogeny, or the development of an organism from a fertilized cell, a few of the duplicated genes are activated depending on the needs of the cell (Ohno 1). The genes that are activated lead to the process of natural selection. In other terms, the activation of several genes, not just a single one is responsible for the emergence of humans.
ReplyDeletehttp://onlinelibrary.wiley.com/doi/10.1111/j.1601-5223.1968.tb02169.x/abstract
-Robbie Thomashow
(diehardcubsfan93@comcast.net)
Sorry about posting the whole thing in three parts. It was too many characters to post it all at once.