Tuesday, April 6, 2010
Human Evolution
In Coyne's chapter, "What about Us?" he discusses the evolution of humans. Coyne says, "Since Dart's time, paleoanthropologists, geneticists, and molecular biologists have used fossils and DNA sequences to establish our place in the tree of evolution. We are apes descended from other apes, and our closest cousin is the chimpanzee, whose ancestors diverged from our own several million years ago in Africa. These are indisputable facts." (p192). Coyne's established that we know where we stand in evolutionary history. We are the most advanced and intelligent race. My question is, how (if at all) do you think humans will evolve? What are some traits/characteristics of humans that are, as we say in class "unintelligent design?" Make sure you incorporate the theme of 'Relationship Between Structure and Function.'
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Because humans are living in a relatively stable condition, the most likely form of evolution for humans will be what Coyne calls "stabilizing selection" (133), which really is when "nothing much will have changed" (133)from generation to generation. However, there are a few "unintelligent" or obsolete features in humans which may produce noticeable evolutionary results in the future. In class, we talked about how the Alveoli of the human lungs just ended on one end creating residual air that just stays in the lungs; this is unintelligent because the residual air is not used in respiration, so the efficiency of the lungs are reduced. Future evolution of humans may modify this trait. Another example of an obsolete trait in humans is wisdom teeth. Current day, humans do not use wisdom teeth significantly, so many people get their wisdom teeth removed. We are already, in rare cases, seeing children born that will not grow wisdom teeth. Human traits that are not fully efficient or are obsolete may be the target for future human evolution.
ReplyDeleteThere are plenty of characteristics of the human body that exhibit 'unintelligent design,' and two that come to mind are the scrotum and the respiratory system of humans.
ReplyDeleteThe scrotum is the sack that holds the testes of a male human. As we all know, it juts out from the body, below the abdomen. Campbell writes that the reason for this is because the scrotum "maintains testis temperature about 2°C below that in the abdominal cavity" (Campbell 1005). The testes need to be held at a lower temperature because sperm maturation occurs at a lower temperature than the temperature of the abdominal cavity. It is my belief that, through evolution, the testes will be able to function at a higher temperature, allowing the testes to be located within the body, instead of in the scrotum. There are mammals who have a low enough body temperature to allow sperm maturation, including monotremes, whales, and elephants.
The respiratory system of a human is also another model of unintelligent design. Humans use negative pressure breathing, meaning that they pull air into their lungs by contracting rib muscles and the diaphragm. The air travels through the larynx to the trachea, to two bronchi, to bronchioles, and then to alveoli. An alveolus is the sight of gas exchange in the lungs of a human. Once gas exchange occurs, air is then expelled out of the lungs due to the relaxation of rib muscles and the diaphragm. When air is expelled, there is a residual volume: an amount of air that stays within the lungs. This means that some of the air inside the lungs is not expelled, and stays inside the lungs until the next inhalation. Also, oxygen-rich air that is being inhaled mixes with oxygen-poor air that is being exhaled. This inefficient respiratory system clearly has flaws to it. In the future, I would like to see humans develop a more efficient respiratory system, such as those found in birds. In birds, oxygen-rich inhaled air doesn't mix with oxygen-poor air that is being expelled. Birds use sacs as a way to efficiently keep air moving within their body. Campbell writes that "ventilation is both more efficient and more complex in birds than in mammals" (Campbell 921). Hopefully, humans will develop a more efficient respiratory system to provide oxygen to our muscles much more easily.
Frank also mentioned wisdom teeth, which is a good example of a part of the human body that isn't really used. Hopefully in the future, humans will not be born with wisdom teeth.
I agree with Frank Wu in that, barring a calamity of epic proportions that makes all forms of technology inaccessible, the evolution of humans will be minimal. The evolution of humans is greatly related to the theme of science, technology, and society.
ReplyDeleteDue to science and medical technology, the pressures of natural selection are no longer as strong. Many diseases and health problems that, a century ago, often resulted in death can be countered today with vaccines and surgery. While not exactly “unintelligent,” the vestigial appendix is a trait that seemingly provides more disadvantages than advantages. As we learned in the animal nutrition unit, the appendix is an extension from the human cecum (Campbell 890). We also learned that the structure of the cecum relates to its function; herbivores, such as the koala, have a very long cecum and digestive tract. The diet of the herbivore consists mostly of vegetation, which is more fibrous and difficult to digest due to the cell walls made of cellulose. As a result, the long cecum provides a greater amount of area and time for the food to be digested and converted by bacteria to a more nutritious form (Campbell 891).
However, in humans, the appendix is not as necessary, since we don’t eat leaves anymore. (For the most part). In fact, the appendix can actually be detrimental, since it can easily become infected and inflamed, resulting in appendicitis. On page 61, Coyne mentions that, of those who develop appendicitis, surgery has reduced the mortality rate from 20% to 1%. Because of this decline in mortality, there is very little selective disadvantage to having an appendix.
We rely on technology so much for our survival which has, for a large part, reduced the pressures of natural selection. We no longer need to hunt for our food, or flee from larger predators (for the most part). However, we are not completely free of selective pressures. As Coyne says, “the sources of mortality are there.” As we learned in the immune system unit today, there are still some diseases, such as AIDS, that have thus far resisted our attempt to conquer them with medicine. If we cannot develop medical technology that prevents these diseases from culling children and reproductively viable adults, it is possible that humans will evolve to combat these diseases. Coyne provides the example of the mutant allele that can provide protection against AIDS infection (219). However, I am doubtful that evolution will be able to beat medical technology, since evolution is, by necessity, much slower than our recent advances in medicine.
I believe that the increasingly competitive nature of human beings to acquire material goods will cause human population as a whole to become more intelligent. In the, relatively, near future there will be a fewer number of procrastinators, lazy people, and those who are are just plain stupid. Unfortunately, this means that my blood line will probably come to an end :(. Companies only hire the hardest workers and brightest minds for the job. Those who are too lazy or are prone to making bad decisions will not be successful. They will become less and less appealing to the opposite sex, so they will not mate and will die alone :(. What may also happen is that humans will split into to different species. The intelligent and attractive species and a not so attractive and dumb species. This could happen due to the fact that there are simply too many people and too much technology for one human to die off or not find a mate. But those are just the psychological adaptations. According to Oliver Curry, evolutionary theorist from the London School of Economics, "Racial differences will be a thing of the past as interbreeding produces a single coffee-colored skin tone." He also insists that "Men will have symmetrical facial features, deeper voices and bigger penises...Women will all have glossy hair, smooth hairless skin, large eyes and pert breasts." Also, others have made a great observation that we will probably evolve to survive without an appendix. Humans no longer need an appendix, which is an extension of the cecum, because the appendix really only serves the function of digesting cellulose and cellulose isn't really a part of our diet.
ReplyDeleteIn the very distant future I predict a collapse to the human species. If we continue to increase the longevity of those who have genetic disorders instead of eliminating genetic disorders, we will become a weak species. An article called "The Degeneration of Man" explains in further detail. It states, "Man, through his inventiveness and energy, conquered his environment through tools, housing, agriculture, clothing, etc. This removed the environmental pressure which maintained our gene pool. Life is no longer totally dependent on youth, eyesight, coordination, bravery, etc. As a result, a genetic cripple may bear crippled children and they may all survive to endlessly propagate the crippling gene. Our species has already declined to below that of survival in the environment of a short time ago, say 10,000 years. If our worldwide civilization should fail, there would be massive death, and perhaps species extinction." So, in essence, our desire to create a short term solution for a long term problem could lead to our demise in the end. Coyne mentions an example of the mutant allele that can provide protection against AIDS infection (219), but unless we use technology to increase the rate of evolution in our favor, a protection of AIDS will not be enough to counter the negative affects of genetic disorders.
Eric Hennings