EvolutionGeneralEvolution is a difficult subject to discuss, primarily because so many come to it with numerous preconceived ideas about it. Most non-scientists and many biologists are quite confused about a proper definition of biological evolution. It is, for instance, very important to distinguish between the existence of evolution and any mechanism that might be proposed for its happening. Paraphrasing the elegant definition of Douglas J. Futuyama, evolution is merely change and is all pervasive. Biological evolution is change in the properties of populations of organisms; individual organisms do not evolve. Evolution is a process that produces inheritable changes in a population and is generally spread over many generations. Another definition of evolution is any change in the frequency of alleles within a gene pool from one generation to the next. And, this comes closer to reflecting what biologists mean when they say that they have observed evolution. What they really mean is that they have detected a change in the frequency of genes in a population. When you look at common definitions found outside of science, you find, for example:
This is terrible. It exclude prokaryotes, protozoa, and fungi, and it specifically includes a term "gradual process" which should not be part of the definition. Other examples include:
These definitions are simply wrong. When someone claims that they don't believe in evolution they are denying something that is pretty easy to demonstrate. It is a lot like saying that one doesn't believe in gravity. Evolution is both a fact and a theory. Common American English tends to regard, "theory" as meaning "imperfect fact" - part of a range of meanings extending from fact to theory to hypothesis to guess. Thus the common perception that if evolution is worse than fact, what confidence can we have in its verity. Evolution is indeed a theory. It is also a fact. And facts and theories are different things. Facts are the world's data. Theories are constructs of ideas that explain and interpret facts. Facts don't disappear when rival theories to explain them are posited. Einstein's theory of gravitation replaced Newton's in this century, but pigs still don't fly. The word, fact, is often thought to carry the connotation of absolute certainty. Not so. There is no certainty in our world. Theodosius Dobzhansky once made a statement that has become very widely quoted by biologists the world over: "Nothing in Biology Makes Sense Except in the Light of Evolution." Evolution is a fact, not a theory. What continues to be debated are questions of details of the process and the relative importance of different mechanisms of evolution. There will be those among you who reject evolution for religious reasons and in general, you oppose both the fact of evolution and theories of mechanisms. You are unlikely to be convinced of the fact of evolution by any logical argument. What you must understand is the nature of the argument that you oppose. You may examine the religious arguments alongside those of Lamarck and Darwin and contemporary biology in the sidebar. DarwinAbout 150 years ago, two men, Charles Darwin and Alfred Russel Wallace, independently collected species from lesser traveled parts of the world. Upon their return to England, they both made hypotheses which could explain the origin of the diversity of organisms that they had observed in their travels. These were presented to the Linnean Society of London in 1858. One year later, Darwin published On the Origin of Species by Means of Natural Selection. An on-line version of the first edition of Origin is available for your examination, if you wish. What in the world was/is so controversial about Darwin's work? Well, his Origin raised a number of serious questions about humanly known and knowable truth. It seriously threatened natural theology in part because of its misunderstood bloodthirsty nature (the survival of the fittest) and in part because of the kind of knowledge Darwin implied was attainable through science. During the 18th century, diversity found in the living world was explained through: (1) Separate Creation, where all creatures were created independently of one another by God and organized into a hierarchy (Aristotle's chain of being) with Man occupying the highest rung just beneath God and (2) the idea that the earth was no more than 6,000 years old. Darwin was not the first to express the notion that evolution occurred. Lamarck, in particular, declared that it occurred. His theory of evolution was a perfectly logical extension of the prevalent view that God had given each species a tendency towards perfection. It held that organisms are not passively altered by their environment but rather a change in the environment causes changes in the needs of organisms living in that environment and in turn causes changes in their behavior. Behavioral changes would lead to a greater or lesser use of a particular structure. Use would cause the structure to increase in size; disuse would cause the structure to decrease in size or even disappear. Lamarck then went on to say that such changes were heritable. Darwin proposed a quite different theory. He had observed that there was a great deal of both structural and behavioral variation present in natural populations and that such variations were largely heritable. Darwin knew quite well that while plant cuttings produced individuals identical to their parent stock, that sexual reproduction produced individuals that differed in many respects from their parents. Variation was a fact of life. Charles Darwin was aware of Thomas Malthus' publication, "Essay on the Principle of Population." Malthus was a political economist concerned with the decline of living conditions in 19th century England. He blamed the decline on three elements: (1) people were having too many children; (2) resources could not keep up with population increases; and (3) the lower classes were irresponsible. Sound familiar? Darwin credited him with a "theory from which to work," and was very impressed with Malthus' statements about people having too many children; and resources not able to keep up with population increases. For all species, it was clear that the capacity to increase their numbers was always greater than just replacement capacity. It struck Darwin that competition for resources in an environment meant that some- perhaps most- must die. This led to the realization that any individual organism with naturally occurring heritable variations that increase its chances for reproductive success will produce offspring which inherit some of these variations. These offspring, in turn, will have a greater chance to reproduce. In time, such individuals will make up a greater part of a population. This selection makes the population as a whole, better adapted to its environment. Once again, it is the population (not the individual) that evolves. To distinguish this kind of selection from directed or artificial selection (the kind practiced by agriculturalists), Darwin called it natural selection. This was Darwin's great contribution. Notions of evolution existed prior to Darwin, however, no good mechanism for it had been postulated. Natural selection provided a mechanism. Evolution arguments make for fascinating reading. You might wish to
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