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Richard Drapo 18 December 1997
BI 301
Dr Wozencraft

Evolutionary Theory

INTRODUCTION
My purpose and objective in writing this paper is to expose the very inward momentum of evolution, how it works, operates and eventually expressing through working mechanisms the very essence of biology itself. Biology is the study of life. In the same way, through evolutionary mechanisms, organisms are propelled through life on a continuous journey. This journey, usually being or seemingly, fixed in time, or miraculously evolving toward an unseen change that usually becomes evident over some period of time. Time can be, either short, a few years or even longer, perhaps, thousands of years.

I will discuss five major hypothesis, such as, Charles Darwins theory of Descent with Modification through variation and natural selection to modes of speciation, hypothesized, to be a driving force in biological evolution. Next, I will discuss the evolutionary mechanisms that are involved in the speciation of plants that seem to be ever changing. And, finally, I will discuss the appearant engines or evolutionary processes that drive life and evolve new organisms through Microevolution...changes below the species level. But, it is seemingly fair to mention that the fuel for life's engines is population genetics.

Population genetics, along with the many modes of reproduction, provide the necessary genetic variations between populations that can actually help to build new populations, or destroy existing ones through morphological or genetic mutations. These mutations, can and do, make species become extinct because of natural selection "survival of the fittest." Species have a hard time adapting to their environments due to their mutations. The prehistoric Irish Elk and the Sabre Tooth Tiger are examples of this. On the other hand, the width of the elks horns and the length of the canine teeth in the tiger probably had purpose, but over time they did not. Could we classify these two morphological traits as being mutations? Yes, because they are an alternation of change in form when compared to todays similiar species. One might ponder on the mere issue of these species, are they really extinct or are they still around, or at least their genes, in todays North American elk or Asian tigers.

Nevertheless, the word evolution has changed in meaning, and has evolved! Evolution before Charles Darwin's time meant the development from a preformed representative in the embryo to the final organism. In Darwin's time, the word meant the progressive development of life from the simple to the complex. After Darwin's time, and up to the present, the word means genetically based, heritable change in one or more characters in a population or species through time. Moreover, it is the latter meaning of evolution that the format of this paper conforms to. I will not address non science ideals, only ideals that can be tested by the scientific method or through experimentation.

DARWIN'S THEORY OF DESCENT WITH MODIFICATION
Who was Charles Darwin? Charles Darwin came from Shrewsbury township in England. On Febrary 12, 1809 he came into this world, of course very different from our own. See figure 1-1 on page 3. A naturalist at heart, Charles enjoyed collecting bird eggs and mineral rocks. When he was in his late teens and early 20's he enjoyed watching birds and noting their habits. It has been noted that while in school charles enjoyed studying chemistry with his brother, and acknowledged this to be the best part of his education while at school (Price, 1996. p. 18).

Many of Charles family were involved in education, and even the publication of books, for instance his grand father published Zoonomia in 1794 which he had read and admired (p. 20). During a five year tenure, starting in 1826, Charles attended two Universities, Cambridge and Edinburgh, located in England and Scotland. It is at these two institutions where he built upon his scientific knowledge and understanding of the natural world.

Subsequently, a letter that would change Charles life arrived in the year 1831 expressing need of a naturalist or scientific observer on board the H.M.S. Beagle an eight masted sailing ship. Charles accepted, and the Beagle set sail December 27th, 1831. He was 22 years of age.

The mission of the voyage was to complete a survey of Palagonia and Tierra del Fuego, Chile, Peru and some Pacific Islands. They would make measurements around the world in order to fix the points of longitude (p. 20). On 2 October 1836, Charles work on the Beagle was completed. During the voyage Charles kept many journals on geology, biology, marine life and the many wonderful animals he encountered (p. 21). The knowledge he acquired from his experiences would later be channeled into writing books and essays. A book, written on Barnacles, experience he acquired by probably having to scrape them off the H.M.S. Beagle is one of his published books.

Consequently, amongst the many Islands in the Pacific, specifically the Galapagos Islands, has often been disclosed as the birth place, or the origination for the book Origin of Species, a book he would later publish in 1859. The book dealt with his theories on Descent with Modification through Variation and Natural Selection. As in the definition of evolution, mentioned earlier in the introduction, this view is no longer recognized, due to scientific advancements in genetics, but it is still very important, and used in the definition of Natural selection. The Modern Theory of Evolution is the revised meaning taken from many of the advancements in the other sciences like genetics, biology, zoology, botany and systematics to name a few.

Variation is a reality that provides the substrate for natural selection (p. 32). Variation is the marked difference or deviation from characteristic form, function and structure or something that is slightly different from another of the same type. A good example of variety can be seen in the wild Rock Dove, Columba livia. See figure 1-2 on page 5. Keep in mind that this is the same species just shown in a number of different varieties.

In addition to variety, natural selection, a big factor influencing variety is the process in nature that causes evolution through differential reproductive success among members of a population; that success depends on genetically based and heritable variation in characteristics that confer relative advantage or disadvantage to the bearer. In the case with the rock dove, natural selection was speeded up through artificial selection by humans. In nature, natural selection influences variation and affects many species usually from parent to offspring through many generations. A good example of this can be seen in figure 1-3 on page 6 of the beak sizes of the Galpagos Island finches that Charles Darwin studied during his five year voyage. Sources of food, and its availability to these birds has been considered a big factor that has influenced heritable variational changes in their beak sizes over a long period of time.

Moreover, the Galapagos finches bills represent Descent with Modification, another meaning of the word evolution. Descent with Modification happens over long or short periods of time. For example, a married couple, working in the mid 70's, studying these same birds on the Galapagos Islands proved this to be the case. In an experiment, over a period of about 20 years, while manipulating food sources, and observing severe weather conditions (drought) they made a remarkable
discovery and were able to document beak size changes among the finches.

Likewise, Descent with Modification can be seen in the genera of horses from the Eocene time era to the present in the evolution of the hoof. See figure 1-4 on page 8. Some might argue that these are individual species, perhaps, but maybe not. It appears to be very good evidence from the fossil record on evolution.

MODES OF SPECIATION
Different modes of speciation exist that has fueled speciation along, or contributed to the diversity of life on earth. The modes include allopatric, parapatric and sympatric speciation models. First, keep in mind that species are spread over large areas, and environmental constraints can help produce genetic variations in populations. The evolution of new species in different localities, resulting from geographic isolation between specie populations is called geographic or allopatric speciation.

In allopatric speciation, a geographic barrier, such as, a mountain range, or a lake, divides a population, gene flow between the two populations stops, and each new population evolves independently of the other, so differences accumulate until the members of one population cannot breed with members of the other, even when the ranges again overlap. Thus, two new species have evolved. Elephants are examples of this kind of speciation.

Second, sympatric speciation, or the establishment of new populations of a species in different ecological niches (habitats) within their normal cruising range of individuals of the parental population is often accompanied by reproductive isolation from the parental species. This mode of speciation is characterized of specialized groups of insects. The Ichneumon wasps (parasitic) are representatives of this kind of speciation.

Finally, parapatric speciation or speciation at the edge of the parentals species range, resulting from a chromosomal mutation that causes reproductive isolation and permits the carrier to invade new adjacent territory in absence of a geographic barrier is the third mode of speciation. This model defines the mechanism that accounts for a pattern of closely related species contiguously disturbed in space with narrow zones of overlap. Wolves are examples of this kind of speciation.

Nevertheless, these three modes of speciation have contributed quite a bit to the diversity of species on earth but, genetics is the driving force that causes new variants of genes being continually added to species populations through mutations that cause new populations to emerge in species. However, when new variants in species arise that fall short of being truely genetically fit, they can become extinct as fast as they emerge.

EVOLUTION IN PLANTS
A major breakthrough in plant reproduction was the development of the seed. Before the development of the seed plants, Bryophytes, members of a division of non vascular plants; the mosses, hornworts and liverworts reproduced by egg and sperm. The seedless vascular plants, such as, the ferns also reproduce by egg and sperm, or spores, see figure 3-1 on page 10. The oldest of these types of plants is known as Cooksonia which were rootless and leafless. Cooksonia looked like green twigs growing on a stem. This plant represents the opening of the flood gates of diversification of the vascular plants (Moore, etal., 1995, p. 699). Seed bearing plants are vascular plants, plants specialized for long distance transport of water and minerals. In spite of the meager fossil record, botanists suspect that bryophytes diverged from a common ancestor to vascular plants more than 430 million years ago (p. 675).

Diversity in plants is expressed through spontaneous hereditary changes or mutations from chromosomal rearrangements and sequence changes in plant DNA. Movable pieces of DNA are called transposable elements. Transposable elements were first identified in the 1940's by Barbara McClintock, whom observed transposable effects on pigment patterns in corn kernels. Hence, the many color variations of Indian corn.

Another mechanism involved in reproduction of plants is polyploidy, a condition in which the number of chromosomes sets in the nucleus is a multiple greater than two of the haploid number in the reproductive process. The word haploid meaning having only a single set of chromosomes. Polyploidy is a common evolutionary mechanism that can produce immediate speciation, and restore fertility to hybrids (p. 562). Reproduction and the restoration of fertility in plant hybrids is endless. Moreover, this is why there is so many different plant species in our world today. Another characteristic of polyploidy is the many similiar species that look very similiar in structure and form. An example of this is the close resemblance of two plant species, in leaf morphology or structure, the first, being Smilacina and the others Disporum (not shown in figure) and Streptopus, see figure 3-2 on page 12. Other examples of polyploidy can be found in the genus Anemone.

MICROEVOLUTION
Microevolution is evolution below the species level. Usually all forms of reproduction, including meiosis, crossing over and recombination of chromosomes in DNA structures fall into this category. Recombination is the exchange of segments between homologous chromosomes during germ cell formation of male and female gametes.

Generally microevolution involves numerous systems, such as, changes in gene frequencies and polymorphism. Polymorphism is the simultaneous occurrence of several different alleles (parts of genes) or discontinuous phenotypes in a population with a frequency of even the rarest type higher than can be maintained by recurrent mutation. What does this mean? Simply, it means a malfunction in the reproductive system that produces mutations in heriditary DNA. The formation of new species can originate from such mutations during gene flow from one individual to another during their reproductive cycles.

Consequently, if species experience such crosses amongst each other and the population is small, and speciation modes are in affect, new speciation can emerge. However, if the species population is large, such mutations can be lost or never realized due to recombination, or the repair of damaged or severely changed chromosomes in the DNA. Usually, when one strand of DNA is damaged, the undamaged strand serves as a template for the replacement of the damaged or mutated, other half of the DNA chromosome structure, or double helix as it is often called in science.

Usually, evolution can't be seen or documented because of sexual reproduction and healthy gene pools suppressing mutations in large populations. However, in a small population where the gene pool or population is small, noticeable changes can occur, especially morphologically and in their ability to reproduce. Right now, this is going on in the small panther population in Florida. Even though these animals appear to be experiencing their dismiss, it is also very possible that geographic isolation or allopatric speciation is happening right in front of our very eyes. According to theory, will the Florida panther change morphologically, due to gene mutations due to inbreeding because their population is too small, less than 100 individuals? According to theory, this cat species should begin to change morphologically in their own time, and maybe, even turn into a new species and become reproductivly isolated from other similiar species.

On the other hand, will their gene pool really begin to mutate and hinder reproduction, as it has been doing, or will natural selection get an upper hand on this species and cause it to go extinct? It is interesting and the possibilities are limitless on a microevolutionary scale. Fortunately, biologists stepped in because extinction possibilities were ever so apparent, due to habitat loss. And, they have even begun to introduce puma's from Texas to help stimulate and encourage breeding.

POPULATION GENETICS
Through out this paper, I have been talking a little bit about population genetics, only because it is very important in all of the evolutionary processes, even affecting the rates of evolution (time). Because evolution occurs in populations and not in individual species, it seems reasonable that its rate might depend on the meantime between generations, as the time of replacement of individuals in the population (Simpson, 1983, p. 154). Similarly, genetic drift, a change in gene frequency between generations, due to sampling error that becomes stronger as populations decline in size is a major influence in population genetics.

Large populations ensures no loss of genes from the gene pool of one generation and no change in gene frequency if natural selection, mutation, and gene flow do not operate, because sampling error is zero or close to it. In a very large sample from the preceding generation, all genes are likely to be represented, and in the same proportions. As the sample becomes smaller, however, the sampling error increases and gene changes from one generation to another become more pronounced (Price, 1996, p. 322). The behavior of a population's genes through generations of sexually reproducing organisms is a crucial aspect of evolution (p. 324). Without the whole population involved in the evolutionary process, evolution probably would be very hard to substantiate or prove.

SUMMARY
To Dr Wozencraft, your question, to compare and contrast where I was and where I'm now at, on evolutionary theory at the start of this class. My response, I'm more fulfilled about biological science. I have often heard it said or phrased, by you, that evolution is the theme or core of biology. Before taken this course, that statement meant nothing to me. After taking this course and reviewing all the biological evolutionary processes, compiled, for this class, into one book, I would have to admit that the above statement is correct.

I figured that evolution was just a small part of biology, and that I could write it off, but I have found out that I can't do this because, in reality, it is a large part of biology. Through out my tenure at LCSC, I have been exposed to evolutionary biology through many text books, or different kinds of classes, and I haven't been able to make any correlations whatsoever, until the completion of this course. Well done.


 References

Hickman, C., Roberts, L., Larson, A. (1995). Integrated Principals of Zoology. Dubuque, Iowa: Wm. C. Brown.

Moore, R., Clark, D., Stern, K. (1995). Botany. Chicago, Illinois:
Wm. C. Brown.

Patterson, P., Neiman, K., Tonn, J. (1985). Field Guide to Forest Plants of Northern Idaho. Ogden, Utah: U.S. Dept. of Agriculture.

Price, P. (1996). Biological Evolution. New York: Saunders College
Publishing.

Simpson, G. (1983). Fossils and the History of Life. New york: Scientific American Books.

This paper was written for an assignment. That assignment being to write a pro paper on evolutionary theory. Note:I am a Creationist, and believe that Evolution is best expressed through Adaptation of a species in the species environment.
-R. S. Drapo

posted by R S Drapo @ 10:24 PM