Evolution or Don't Jump off the Cliff!
The theory of evolution is perhaps the most controversial and misunderstood theory in science today. To understand evolution we must first examine it in the context of the nature of scientific theories. A scientific theory is an interrelated set of very well tested assumptions and hypotheses the explain some large set of phenomena in the natural world and provide a framework for further experimentation. Examples of theories in science include; plate tectonics in geology, relativity in physics, gravity in astronomy, and thermodynamics in chemistry and biology. The theory of evolution is a theory in this scientific use of the word theory and evolution is also a fact. We know that it happens even if the theory is incomplete
First evolutionary theory has a set of well tested assumptions:
1. Physical laws that are operating today operated in the same manner in the distant past. This assumption is called uniformitaritanism and allows us to interpret the fossil record in terms of physical processes happening today. For instance, scientists can infer a lot about dinosaur tracks and the dinosaurs that made them just by applying what we know about analogous tracks made by living animals. It also allows us to use decay of radioactive isotopes to determine the age of fossils.
2. In theory all events in the past, just like events happening now, can be explained by these physical laws. In other words there is no need to invoke the Creator to explain how anything living or not came about. This, in my opinion, does not deny the existance of a creator but merely that any gaps in our knowledge should be assumed to be due to ignorence on our part.
3. The cell theory: All cells arise from preexisting cells and all living things are made from cells. Under current conditions spontaneous generation does not exist. This set of assumptions is important to biology because it postulates a continuous line from living cells to cells that once existed in fossil organisms when they were alive. The cell theory is basic to biology and failure to accept evolution would imply spontaneous generation under conditions very much like today's. Of course, conditions when life first arose were quite different from today's conditions. For instance , the atmosphere is assumed, with very good reason, to not have had much if any oxygen.
Next consider the well tested hypotheses of biological evolution:
1. DNA replication is not perfect and gives rise to new variation in phenotype or potentially new variation in phenotype. Many times people have the idea that all mutations are bad. This is just not true. All you have to do is look around at the multitude of genetic variation in people. In a class there will be people with different skin color, hair and eye coloe. nose shape...etc. Much of this variation is under genetic control....how did this variation come about except for mutation? That mutations can arise has been well studied in organisms and that these mutations are not always bad is well known as well. Indeed some scientists called neutralists, believe that most mutations actually have little or no immediate affect on the survivorship the organism carrying them.
2. Evolution is a population phenomenon that can be explained by different combinations of the following ideas:
a. Populations vary in size through time and are finite in size. This leads to genetic drift.
b. Natural selection operates in populations
c. New mutations are constantly arising in a population
d. immegration and emmigration may occur between populations.
e. mating among individuals in a population may be non random.
If you've had biology, you may recognize these five ideas as the reverse of the famous Hardy Weinberg Law of equaibrium. The Hardy Weinberg Law sets up conditions under which evolution will not ocurr. Thus, it operates much like the ideal gas in chemistry. A little thought and analysis of the literature of evolutionary biology will show that much of the literature involves studying systematic violations of the Hardy Weinberg Laws.
3. Of course there are, if you check any biology text, two types of evolution: microevolution and speciation. A basic hypothesis is that no special mechanisms are needed to explain most cases of speciation(development of new species). Creationists often claim that there are no examples of speciation observed today and therefore this type of evolution cannot be scientifically tested. First of all even if this creationist claim were true, it would have no bearing since the creationist alternative to evolution namely special creation is itself non-scientific, inspite of the claims of "scientific creationists". Also, just because something is not observed today doesn't mean that one should immediately jump to creation as an excuse. Astronomers cannot see stars being created today but rely on the patterns of light reaching the earth from millions of light years away to infer that the creation of stars is not an all at once process but follows a regular set of patterns.
Further, there are examples of speciation happening today, A good example involves a set of lungless salamanders in California. Furthermore plants frequently form new species through hybridzation and polyploidy.
Thus, we see that evolutionary theory has a well tested set of assumptions and hypotheses that compose the theory. This does not mean that we have a complete understanding of evolution. For instance, there is much we do not know about speciation. Some scientists believe that species can arise quite rapidly from pre-existing species by a process called punctuated equilibrium. This process itself is not well understood either and that such a process exists is supported mainly by the fossil record. Even in terms of micro-evolution we still do not understand entirely how many adaptations(e.g. sexual dimorphism) can arise. However, biologists do not scrap an entire theory because there are some things that the theory cannot explain. After all, none of these things contradict the theory, but rather the theory is not well enough developed to explain them. This distinction between contradiction and the theory not being developed enough to handle certain problems is lost on many creationists.
Indeed, the best analogy I can think of to this last point is to consider theories of gravity. Using the logic of many creationists concerning the exisitance of evolution, we would be forced to argue in the following way. Physicists argue about gravity. Therefore gravity must not exist. Clearly this logic is false here and it is equally false for the the creationist's arguements against evolution. If you choose to believe creationism as being science then what you are doing is the biological equivalent of jumping of a cliff because, after all, gravity does not exist.
Links in this page are from the Talk.origins web site. Definately worth a visit. Talk.origins is also a usergroup(newsgroup) and the web page will tell you how to access the newsgroup. Talk origins is mainly concerned with scientific approaches to the orgin of life and the evolution of species. Thus, it is not a creationist site. However, the site does provide links(and sometimes commentary) about creationist sites.
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© Paul Decelles September, 1996 revised 9/5/99
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