Species Divergence - Essay Example

?Synthesized Essay First and e-mail, login information> Species Divergence a. In most general terms, biological evolution maybe defined as the accumulation of changes in inherited characteristics of a species that gives rise to significant alterations in its biological organization, i.e. physiology, the mode of interaction with its environment, nutrition regime, etc. While evolutionist ideas may be discerned in several pre-modern scholars’ ruminations, it was only with the advent of the 18th century Enlightenment that modern evolutionary theories formed, with that of Charles Darwin soon taking the pre-eminent place among them. The formation of currently mainstream version of evolutionary biology was immensely helped by the respective advances in the fields of genetics and molecular biology, which helped define the organic basis for evolutionary processes. From a biological organization point of view, evolution proceeds on a species level, as individuals comprising a species do not themselves evolve over the course of their lifespan. However, the results of their interaction with the environment enable the accumulation of new heritable responses within their genotype structures, giving rise to a process of natural selection. The latter, in its turn, conditions the changes in the species’ phenotype (i.e. the complex of biological features). Natural selection may be properly defined as a gradual process of genetic variation whereby the individuals with most favorable gene combinations are more frequently able to transplant their genes to subsequent generations of a species, so that their descendants will define the face of their species. While natural selection process is individual, being transmitted across a species only indirectly, it is genotype of a species as a whole that it impacts on, so that heritable changes in those individuals’ genotypes that are favored by natural selection are spread to the subsequent generations of a species as a whole. The mechanisms of natural selection are varied; however, some of them may be assigned more prominent roles in its perpetration. Of those, ecological selection, with an emphasis on fitting with one’s biological environment, and sexual selection, with an individual’s fecundity and ability to find prospective sexual partners as a key factor, may be considered the primary ones. In turn, these mechanisms may be sub-divided into more specific methods of selection, with, e.g., ecological selection encompassing the mechanisms of intraspecies competition, kin selection, etc., and sexual selection including those of intrasexual selection, intersexual selection (sexual dimorphism), etc. b. Evidence for biological evolution is manifold and comprises the number of data from different scientific disciplines. Within the context of this essay, five types of this evidence will be examined. Plate tectonics. The discovery of the movements of plates in the 20th century laid to rest the notion of unchangeable nature of Earth’s tectonics, contributing to an idea of nature’s propensity for change. On a more specific level, Charles Lyell’s studies on the impact of climatological and geological changes on the distribution of species, with specific emphasis on extinct flora, led the researchers to conclude that movements of large land masses lead to conversion of climates, which meant that animal and plant species had to be dynamic entities, the spatial distribution whereof changes in accordance with the changes of topography brought about by geological agents. Consequently, the changes in floras and faunas were decisively connected with the corresponding shifts of land masses, contributing to the development of an idea of ecological selection. Biogeography. The research in the connection between plate tectonics and changes in life on Earth that was referred to above has been directly connected with the research in the field of biogeography. Such scientists as Edward Forbes, Wallace and Willer Matthew conducted an extensive research in the distribution of species groups across the continents in the late 19th to early 20th century, reaching a conclusion that several zoogeographical provinces may be identified, each connected with the specific group of species spreading from the center to periphery of the province. According to Matthew, such geographical factors as “inaccessibility to invasion” have direct impact on the primitive or advanced character of this or another zoogeographical province’s animal population. In this aspect, the development of geographical barriers known as the vicariance has been proven to have had an impact on the speciation and differentiation of the groups having common ancestors. Stratigraphy. The stratigraphic records of the Earth are indispensable evidence of the past life forms that used to dwell on our planet and, as such, they may be considered some of the most important portions of evolution’s evidence. The changes in stratigraphic layers usually coincide with the passing of the previously dominant life form clusters, as the mass extinctions noted for the periods of transitions between certain geological periods (such as Permian-Triassic or Cretaceous-Paleogene extinction events) testify. The study of different stratigraphic layers and their succession allowed the paleontologists to construct a narrative of successive life forms in the history of the Earth, supporting the thesis on dynamic and evolutionary nature of life as we know it. Fossils. The fossilized remains of extinct animals, plants and other organisms that are found in different stratigraphic layers of the Earth’s surface (see above) may be considered the most persuasive evidence for evolution. As the correlation between respective time frames and the life forms found in their stratigraphic layers became clear, it has been possible to establish the line of development of these life forms from the rise of the first organic life to our geological times. In addition, the existence of fossils enabled the scientists to compare their phenotypes to those of currently existing animals and plants, constructing often elaborate evolutionary genealogies. Molecular biology. The advances in genetics, with the discovery of the DNA being most important of them all, allowed for uncovering the organic basis of evolutionary changes. The genetic information was found to serve as a medium wherein the heritable responses to mutability of the environment may take shape. In addition, the laboratory experiments on microorganisms (such as bacterial life), which possess rather small lifespan individually, served as the field evidence for the existence of mechanisms of natural selection, as the successive generations of bacteria used in the experiments followed the patterns of inheritance that were provided for in the theories of natural selection. This may be considered their most conclusive proof of all. c. The Hardy – Weinberg principle provides a case of fictional allele frequencies equilibrium that would allegedly be in place, if no evolutionary process occurred. The Hardy – Weinberg equilibrium may be ostensibly characterized by the following 5 conditions: 1. No mutations occur, and no new alleles enter the population; 2. No gene flow occurs (i.e. there is no migration of individuals into, or out of, the population); 3. All mating is random; 4. The population is so large that no genetic drift may possibly lead to changes in the allele frequencies. 5. No selection occurs, and no alleles are selected for, or against. However, it is clear that the existence of mutations, the migration of individuals of the same species from one area to another, mating in accordance with the results of sexual selection, the frequent diminishing of natural population, and the constant impact of ecological selection are indispensable features of life on Earth, daily registered by the scientists. This means that the Hardy – Weinberg equilibrium is in fact unattainable, and, therefore, evolution process actually takes place. d. The divided and isolated populations of the same species are necessarily prone to the prospects of speciation, eventually forming a distinct species, due to several factors at work. The most important of them is that of reproductive isolation. Prevented from receiving the usual gene flows from the other populations of their species, a now isolated population gradually comes to be characterized by specific heritage responses that gradually accumulate, and by specific mutations having their impact on a population’s genotype. Gradually, reproductive isolation leads to an inability of the population to interbreed with its former species, marking the former as a new species altogether. Some other factors bringing about isolation and speciation may be mentioned here as well, e.g. temporal isolation (the split in populations in accordance with their differing time cycles); allopatric isolation (caused by geographical barriers, etc.). However, the most important reason, after all, is divergence in environmental challenges experienced and the lack of gene inflow from the core species population. Literature Cited Bonner, John Tyler. 1988. The Evolution of Complexity by Means of Natural Selection. Princeton, NJ: Princeton University Press. Briggs, John C. 1988. Biogeography and Plate Tectonics. 2/e. Amsterdam, The Netherlands: Elsevier Science Publishers B.V. Hall, Brian K. and Benedikt Hallgrimsson. 2008. Strickberger’s Evolution. 4/e. London: Jones and Bartlett Publishers. Friesen, Larry Jon. 2012. Biology 150: Biodiversity Lectures. Evolution. http://www.diversitynotes.net/biodiversity/text/01evolution/index.htm. Friesen, Larry Jon. 2012. Biodiversity 1.0. Santa Barbara: Nature Journal. Read More