Posted by: Hope | November 23, 2009

Evolution: Not Just a Theory

This is a paper I wrote one evolution. Enjoy 🙂

Evolution: Not Just a Theory

Evolution in a very broad sense is merely change. Biological evolution is the change of a population over a period of time.  When genetic material changes from one generation to the next, it is considered to be evolutionary (Moran).

If we take dog breeding as an example, we can see how natural variation and selection can change species in a profound way. For example, dog breeders will have a set of dogs and choose which dogs breed with each other. The breeder is basing this off of the different types of traits that will make the dog that the breeder wants (Onstott). In actuality, whether the breeder realizes it or not, what they are actually doing is selecting genes each dog has. Over a period of time the genes in the dogs’ pool will change, causing the vast variety of dog breeds we have today.

If you’ll notice though, this is an example of artificial selection, not natural selection. Using this example, natural selection works exactly like the breeder, but instead of a person sitting around selecting what should go with what, it happens due to simple survival or better reproduction.

With this being artificial selection, natural selection works in a slightly different way. In wild species will change over time due to natural selection. This occasionally has different groups of the same species diverging, eventually giving us all of the diversity we see today. Organisms are all related by common descent, with the different forms coming about, due to natural selection operating on random mutation.

Have you ever wondered why trees are tall? If trees were shorter they’d spend a lot less energy. It takes more energy for a tree to grow tall compared to short. We come to this conclusion because the thicker trunks of the tall trees take up more energy. Smaller trees are lighter and consequently do not need a thick trunk. However, with evolution small trees are unstable. If the plants are close together taller plant will dominate, taking up all of the sunlight. Therefore, in this case the taller tree is more fit (Dawkins p. 20).

Imagine that trees were just bushes, located closely together.  Then suddenly a mutation occurs at random, causing one of the trees to be slightly taller than the rest. Due to this that tree would take up more sunlight than the rest. Because of the access of more sunlight the taller tree is able to have more offspring than the rest of them. This causes the tall tree gene to spread through the area. Then another mutation occurs causing another tree to be a tad taller than the others, causing another domino effect of the trees having to grow even more. Eventually, you get to the point where we are now, with an entire forest full of tall trees. This is wasteful and unnecessary because now that all the trees are taller they are taking in the same amount of sunlight as they were when they were smaller, but wasting a lot of energy growing taller.

Another piece of evidence for common ancestry is a gene found in all mammals called gulonolactone oxidase (also known as the GULO gene). In most mammals, this gene contributes to the production of Vitamin C.  However, in all Haplorrhini (“dry nosed”) primates, though we contain the gene, it is broken.  By broken I mean, it is missing a single base pair. Since DNA works on a three base pair sequence, losing one base pair interferes with the entire system and the gene no longer functions (Fairbanks p. 53). This leaves us incapable of producing Vitamin C. The most interesting part about this is that not only do humans contain this broken gene, but all primates do.  Not only is it the same broken gene, it is the exact same base pair that is missing. The probability of approximately 200 different species having the same sequence is ridiculously unlikely to have just happened. Intelligent design has no explanation for this, nothing to test. However, with evolution you can find the chances being much more likely. If primates evolved from a common ancestor that lost function in this gene, then that error would have simply been copied from the original primate that had the mutation.

Though the above evidence is exceedingly strong, perhaps a more visceral example of how life just doesn’t make sense without evolution is the laryngeal nerve. The laryngeal nerve is the nerve that supplies motor functioning and sensation to the larynx (also known as the voice box). The interesting part about this nerve is the path it takes, which is a very circuitous route.  The left laryngeal nerve branches down and around the aorta, before coming back up (Gray pg 912). The right laryngeal nerve does the same thing, going down and around the aortic artery. The route is unnecessary, but occurred due to evolutionary purposes.

The nerve first came about in fish, and began by connecting directly to its target. Also, this is exactly what our embryo does, but then tissues move and shift around enough to make shapes we are familiar with. It just so happens to move and shift around to position at which it loops down and around the aortic artery. But since it looped around in the embryonic stage, it did what it had to do by making the nerve longer as we began to develop further. The reason it originally looped around was actually very random. It did not cause any extra costs to the early animals to have it loop one way or the other. I find this even more unnecessary with animals such as the giraffe, with very long necks. The laryngeal nerve in a giraffe also does this, by branching all the way down its long neck, around the aorta, and ascending back up.

For a better understanding allow me to quote Richard Dawkins from his book The Greatest Show On Earth:

During the evolution of the mammals, however, the neck stretched (fish don’t have necks) and the gills disappeared, some of them turning into useful things such as the thyroid and the parathyroid glands, and the various other bits and pieces that combine to form the larynx.  Those other useful things, including the parts of the larynx, received their blood supply and their nerve connections from the evolutionary descendants of the blood vessels and the nerves that, once upon a time, served the gills in an orderly sequence.  As the ancestors of the mammals evolved further and further away from their fish ancestors, nerves and blood vessels found themselves pulled and stretched in puzzling directions, which distorted their spatial relations one to another.  The vertebrate chest and neck became a mess, unlike the tidily symmetrical, serial repetitiveness of fish gills.  And the recurrent laryngeal nerves became more than ordinarily exaggerated casualties of this distortion (360).

One thing that must be pointed out is that these are not the only arguments to support evolution. Evolution is such a broad area to study, that it would take much longer to explain every little bit. Nobody ever made the claim that evolution is not complicated, it is. These examples are very minute, and tiny, to explaining what evolution is and why you should believe in it. Another point is that evolution is what makes biology make sense (Dobzhansky).  The examples I have introduced are nothing very striking examples of the statement that biology does not make sense without evolution.

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Responses

  1. Many college credits in Bio later, I found out that this could not occur without intelligence. The 2010 Ford did not evolve, although it has parts in common with the model A. There was a designer.


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