Coyne lists and explains the six components making up the evolutionary theory from pages 3-13.
1. Evolution
2. Gradualism
3. Speciation
4. Common ancestry
5. Natural selection
6. Processes other than natural selection can cause evolutionary change
Some of these elements are very similar, and all six intertwine ideas and concepts with the others. Choose two or three of the elements to describe, distinguish between and compare. Also, describe how the elements you choose relate to each other. (For example; how are evolution and gradualism different? what do speciation and common ancestry have in common?)
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One of the most obvious and primary compoents making up evolutionary theory is evolution itself. On the most basic level, Coyne describes evolution as meaning "a species undergoes genetic change over time" (pg. 3). So over the course of many many years, a species can change into something very different, based on changes in DNA that come from mutations. If we look towards certain organisms in particular, we can see that these organisms (humans for example) were not around millions of years ago, but rather evolved from species that did live in the past. Also, Coyne makes the point that evolutionary changes do not all occur at the same rate. Some species like horseshoe crabs and gingko trees take millions of years for any type of evolutionary change, while other species such as whales and humans evolve rapidly. However, evolutionary theory does not predict the rate of evolutionary change in a species.
ReplyDeleteGradualism, another component of evolutionary theory, is the idea that it takes many generations to produce any significant evolutionary change; for example, the evolution of birds from reptiles as seen on pg 4. Now, in the evolution component we just discussed how evolutionary theory does not measure the rate of evolutionary change, and that different species have different rates of evolution. However, the component of gradualism addresses only ver substantial evolutionary change, not merely evolutionary adaptations. For example, the evolution of new features: teeth, jaws, are considered substantial changes that by the component of gradualism requires millions of generations. There are certain changes that do occur quickly, as described in the evolution component. For example, drug resistance in disease-causing bacteria arises with uncanny speed. However, basically, when we speak of gradualism, we speak of big change. Gradualism does not mean that every species evolves at an even pace. A single species evolves faster or slower according to evolutionary pressures. When natural selection is strong such as in a newly colonized area, evolutionary change is relatively faster than in a stable habitat. In th ecology unit earlier this year, we learned about how natural selection is related to evolutionary adaptations; natural selection maximizes a specie's sucess to survive and reproduce through evolutionary changes (Campbell). Here we can see that if there is stronger natural selection, these evolutionary changes actually occur faster.
These component of evolutionary theory of course relate to the theme of evolution. Basically, evolution accounts for the biological change of organisms that occurs over time and is driven by the process of natural selection (pbs.org/evolution) Evolution accounts for the diversity of life on Earth. So when organisms go through evolutionary changes due to the environmental pressures, these organisms will eventually, after many many generations, go through substantial changes (gradualism). Furthermore, this idea relates to the theme of continuity and change. This theme basically refers to how all species tend to maintain themselves from generation to generation using the same genetic code. However, there are genetic mechanisms that lead to change over time, or evolution. Clearly, the mutations in DNA coding that lead to evolutionary changes (evolution component) demonstrates that there is eventual change over time. Thus, the two components evolution and gradualism are similar, yet address different aspects of the overall evolutionary theory.
I agree with Connie's assertion that evolution happens at different paces for different species. For example, the last journal article I evaluated featured weeds that showed different changes in gene expression after a short period of 12 generations. The weed began producing non-dispersing seeds instead of dispersing seeds as the weed was moved into a plot where seeds would land nowhere if dispersed too far. Scientists don’t always see these changes this quickly in all organisms.
ReplyDeleteSpeciation is caused when breeding populations are reproductively isolated from each other (Coyne 172). It is most easily described by the biological species concept (BSC) by Ernst Mayr and Theodosius Dobzhansky. Speciation has given rise to the many species of sharks in the sea. For example, black bears live very far from polar bears. Their diets are different as well as their morphology. This is because of the adaptations to their environments.
In other words, morphological and dietary changes are altered by processes other than natural selection that can cause evolutionary change. Grizzly bears have a prominent muscle over their shoulders (I learned this during a tour to Yellowstone National Park). This muscle allows the bear to dig for food. letting the bears hunt for bugs.
However, the polar bear is very different, being almost all white. The white coloring allows the polar bear to blend in with its surroundings, letting the bear catch prey more easily. The polar bear also has blubber that allows the polar bear to conserve heat while hunting in the Arctic waters.
Thematically, the grizzly bear’s hind shoulder muscle and the polar bear’s white fur are connected to the theme structure and function. These structures provide selective advantages for the bears to perform tasks that allow them to forage.
A similarity between these two elements that facilitate evolution is that both provide diversity. If there wasn’t speciation in the world, then there would potentially only be one animal per genus. Campbell, in figure 1.14, shows that there are bears belong in the Genus Ursus (12). Each species provides more species diversity on Earth, and environmental processes help facilitate these changes in species diversity.
Ultimately, however, I believe that processes other than natural selection drives speciation. The difference between these two elements, metaphorically, is that natural selection’s processes provides the background of evolution, while speciation provides actual, distinguishable differences between each organism. As Coyne notes, there are factors such as geographical (175, 178), natural selection (177), and genetic (180) that drive speciation. And I doubt he was able to note all the myriad other factors that drive speciation. If these factors didn’t exist, then there would possibly be a huge crackdown of species diversity in this world.