On page 141, Coyne explains how complex organs like the eye would have been created over the course of time by giving a series of examples with intermediary steps of said organ as can be found on animals today. But how could natural selection ever dictate that a blood vessel as crucial to the proper functioning of the body like the carotid artery would be placed so close to the surface of the skin, exposed and in great risk of being accidentally cut? This is just one example, another being the spinal column. It is illogical to think that such an important part of the nervous system would be surrounded by vertebrae and gelatinous discs that with one false move can sever the spinal cord and majorly disable a person. What other illogical body parts exist on humans that are either too vulnerable or exposed for natural selection to warrant their placements? On other animals? And how can evolution explain these simple vulnerabilities?
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Another example of a badly designed body part is the knee. A well designed knee would, according to Mr. Erdmann, be the backwards version of our knee right now. It would be able to take the pressures of bipedal walking. But, since evolutionary theory states we evolved from animals that walked on all fours, our knee is well suited for quadrupeds. The illogical placements of the spinal cord and carotid artery can be explained by what Jerry Coyne calls bad design. According to Coyne's blog (Why Evolution is True), other examples of bad design include the useless eyespots of blind cave fishes and the lengthy recurrent laryngeal nerve (much longer than need be) are both examples of bad design. The eyespots of cave fishes are a bit more vulnerable than the rest of their body. The placement of the the carotid artery can be explained by evolution. According to evolutionary theory, our whole neck area is analogous to the gill areas of fish. The gills of a fish are the sight of their respiration and host to many blood vessels, big and small. But, as animals started to move out on land, gills became unnecessary. Instead, respiration became handled in the lungs. But, the brain still needed oxygen from the lungs. Instead of creating whole new arteries to reach the brain in a safer place, it isn't hard to envision the same vessels that were used as respiratory arteries in fish to be used in transporting blood to the brain. The carotid artery is in its vulnerable spot because gills were always on the side of a fish's "neck".
ReplyDeleteJonathan, you mentioned that the eye is exposed and vulnerable to harm. However, the importance of the eye massively outweighs the harm that would be done to an organism of the tissue was damaged. Another point is that natural selection had added "defenses" for eyes. The existence of eyelids, which blink to refresh the eyes with tears that wash out bacteria and foreign invaders, and eyelashes prevent dust from falling into the eye.
ReplyDeleteEvolution has shown to have many uncharacteristically badly designed traits, however, it also shows many ingenious ways to fix these problems. For example, the esophagus--which evolved from primitive gill-like structures in our ancestors, shares the same tube fore breathing and eating. Despite this, choking doesn't happen every time that people eat because of a flap known as the epiglottis which blocks food from falling into the larynx. Another example of originally badly designed structure would be the birth canal of women. Having recently evolved from quad- to bipedal movement, humans had to make a humongous adjustment in the skeletal and muscular systems. After this rapid evolutionary adaptation towards bipedalism, human females now had to give birth between hips that were tightly closed off due to the need to support the rest of the body. Now, childbirth is a difficult and painful process, but not an impossible one. The adaptation of various hormones such as oxytocin that stimulate the the uterus to have contractions that push the baby out.
There are many examples of seemingly terribly designed body parts in humans, but evolution cannot allow proliferation of a trait that inhibits survival and reproduction. So what might seem like a negative aspect is usually outweighed by the positive outcomes such as sight, nutrition, and continued reproduction.
Sources:
Biology book
Why evolution is true
http://en.wikipedia.org/wiki/oxytocin
Another example of how a precise blow in could completely disable a person is how a well-placed, forceful uppercut at the nose could cause the bone to fracture, piercing the brain and killing the individual. However, this example, just like the others that you listed, require extreme amounts of force or occur in some sort of freak accident. As Tianyu said, the benefits that we get from having these things, maybe in a spot where they are relatively more exposed than other vital organs, greatly outweigh the risk that we have in injuring them. Just like the eye has eyelids and eyelashes to protect them, your other examples have protection mechanisms that make it extremely difficult for these properly named freak accidents to happen. Yes the carotid artery is much more exposed when compared to the other important arteries in our body, it is still well protected by our skin. It would take an extremely deep cut in order to get through the skin and the carotid artery. As with the spinal cord, while it does seem logical that we would have a deeper mechanism of defense for something so vital, the vertebrae do an outstanding job of protecting the spinal cord from injury. Again, it would take a freak accident to cause an injury that would break the vertebrae and cut through the cord. The reasons that deeper lines of defense haven't developed for these parts is because the defense mechanisms that we already have do a sufficient job of protecting these vital organs and parts. Injuries to these are very serious, but also very rare. The rarity of this type of injury is what has enabled these defenses to evolve and stay the way they are. It is such a rare occurence that these injuries happen, that there has been no real evolutionary pressure to evolve a better defense for these organs and parts.
ReplyDeleteOn page 13, Mr. Coyne described the development of the human male testes, calling it a "tortuous testicular journey" (13). This complex process begins with the testes developing in the abdomen, then migrating down into the welcoming scrotum, but leaving "weak spots in the body wall that make men prone to inguinal hernias," which can in some cases cause death. (13) This is another example of "bad design" that natural selection could only "make the best of" because it doesn't create, it only modifies. Coyne asks the reader why a creator would create such bad design, if it meant pain for many men. Yet this is another point where Coyne assumes that the creator would have human motives in designing his/her/its creations. Coyne subconsciously places his own objective if ever given the opportunity to create on God: to design the most well adapted organisms for survival in their particular environment. Yet Coyne ignores the idea that there is a chance that if by a long shot creation is true, perhaps the creator produced flawed organisms on purpose.
ReplyDeleteAnother example that Coyne gives is the plight of the sea turtles, who "dig their nests on the beach with their flippers---a painful, slow, and clumsy process that exposes their eggs to predators," and Jerry suggests that they would have done better with "retractable shovel-like appendages" (12). These flippers aren't suited for their job, or at least for one of their many jobs. Perfection is impossible, from a creationist and evolutionist standpoint.
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ReplyDeleteThere are many examples of poor design in evolution; things that, as humans, we see a much more efficient method by which we would design animals in order to give them a greater survival rate, but what must be remembered about evolution is that it must reuse or build on old parts. This means that if we were to create- from Brady's example- a more efficient turtle, then there would need to be a preexisting limb which could be slowly reshaped into "retractable shovel-like appendages" (Coyne, 12). Though evolution has produced a radically diverse set of species all these species have evolutionary remnants of their ancestors, and all of the traits found on an organism must be traceable to previous features found in that particular organism. Like Sang said, the carotid artery is placed in such a vulnerable spot because it comes from the gills. Evolution simply took something that already works and tweaked it to get a new use out of it, and because it serves the purpose of transferring blood well enough that adaptations (such as new sets of more protected blood vessels)are unnecessary. As to the subject of the blind cave fish, this simply reinforces this idea. The blind cave fish have no use for their eyes, but because of their popularity as pets (and therefore being human bred) and the relatively small amount of vulnerability that is a result of these eyes, evolution hasn't weeded them out yet. It supports the argument because it shows that despite their uselessness evolution must leave them there or slowly weed them out because evolution does not make things happen out of thin air, but instead adds, removes, or changes old processes.
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