Biological evolution is described as the genetic change that takes place in a given population from one generation to another. There is a significant variation with regard to the direction of change and the speed of evolution among the different species and at varying time line. Evolution that is continuous evolution can take place over numerous generations that can result to the development of new biological species and varieties. On a similar account, failure to evolve as a response mechanism to the environmental changes is likely to result to cases of extinction of a given species (Starr 265). Evolution is a widely consent topic my scientists, who are of the view that evolution is not just a mere speculation, rather a theory which requires adequate fundamental testing to be proved through the use of empirical evidence in order to conclude that evolution took place. There is massive evidence that has been accumulated that can be used as an evidence of evolution. All forms of life and human beings were subject to evolution from earlier species and that all living organism are still evolving. The evidence for evolution taking place and continues to occur is based on four primary sources including the change in the fossil records of the earlier living organism species, similarities in terms of chemical and anatomical forms of related organisms, geographic distribution of species that are related and documented changes in the genetic makeup of living organisms over a number of generations.With regard to the evidence that draws on the fossil evidence, the remains of earlier species of plants and animals that are fund in the sedimentary deposits of rock provide uncontested evidence of the changes within similar species over a large period of time. This evidence of evolution affirms the fact that there has been a variety of species and that some species that were subject to extinction possessed characteristics that were somewhat transitional between a numbers of existing organisms. This evidence serves to confirm that living species are not fixed; rather they are subjected to evolution to form other species as time goes by. The evidence by changes in the fossil records of early species of living organisms also reveals that the gaps observed in the fossil records are mainly due to incomplete data collection. In addition, the more one goes deeper to analyze the evolution of a particular species line, the more the transitional specimens come in to fill the gaps in the fossil records. For instance, one of the notable gaps in the fossil evidence records that were filled was the gap between small bipedal dinosaurs and the birds species. In addition, after Charles Darwin documented , an old fossil of archaeopteryx of approximately 145-150 million years was located in the Southern region of Germany. The fossil had jaws and teeth and bony tail that were similar to that of the dinosaurs. This is further used to affirm the view that birds species evolved from reptilian ancestors. Other vital evolutionary gaps have been filled, especially the gaps between aped and human species. Therefore, the changes in the fossil records offer adequate evidence that the complex plant and animal species existing today came from earlier simple species (Starr 275).With regard to the evidence of the similarities in chemical and anatomical structures, all living organisms that are found in the earth are basically similar in terms of chemical compositions and anatomical structures. All species irrespective of complexity all start as single cells that are reproduced by same cell division processes. In addition, all the living species have a common characteristic associated with the creation of complex molecules from carbon and other elements. It is not just a coincidence that about 99 percent of proteins, fats, carbohydrates and other vital molecules that make up the living species are from six of the ninety two most common elements found on earth. All the plant and animal species usually get the traits from their parents through the transmission of specific combinations of the genetic material. Molecular biology affirms that genes are a segment of the DNA molecules. The basic evidence is that irrespective of the diversity of the species, the simplicity of the language of the DNA code is similar for the living species, which serves as an evidence for molecular unity of life. Similar anatomical structures are for the case vertebrates, where by all the animals posses internal skeletons. Anatomical inheritance implies that these features were inherited from a single ancestor.Other clues that can be used as evidence of evolution include the geographical distribution of species that are related and changes in the genetic makeup of species over time. Owing to the fact that the environment is persistently changing, organisms adjust their genetic makeup in order to survive the in the new environments, as a result, most of their traits will be evident in the following generations. This is what Darwin referred to as natural selection. For instance, the evolution of bacteria is resistant to antibiotics is an perfect evidence to affirm this claim. This is the case for the ancestral canine-like species including the wolf, dog and the fox.The mechanisms and processes of evolution attempt to affirm the various processes that facilitated evolution among the living species. Key concepts covered in relation to this issue involve the fact that populations evolve the patterns of the process of natural selection, cases of micro-evolutionary processes, how the various species arise and the patterns of macro-evolutionary processes. Genetic variation is central to the process of evolution through which selective forces can kick start the process of evolution. The process of evolution comprises of two main parts including the reproducing mechanism that the organism uses to create a variety of organisms and the changing environment that serves to compel the organisms to change. Therefore, the process of evolution focuses on a number of factors including descent and the differences in genetic structures that are passed on to the following generations; mutations, gene flow due to migration, drift in genetic structure and natural selection as the evolutionary mechanisms of change; the significance of genetic variation; the undetermined nature of the genetic drift and the potential effects associated with the reduction in genetic variation; how variations, heredity and reproduction that is differential can compel natural selection to take place; and how diverse species affect the evolution of other species through co-evolution. The Neo-Darwian perspective of evolutionary processes centers on natural selection, biased mutation, genetic drift, gene floe and genetic hitch-hiking, which are the fundamental mechanisms of change.Evolution through natural selection takes place when genetic mutations serve to enhance the process of reproduction to result to the survival of that mutation in subsequent generations. Natural selection draws on the fact that heritable variation is present within the populations of a species, organisms tend to produce more offspring that has the capability of survival and that these offspring have different abilities in relation to their survival and reproduction. Such a state of affairs is likely to result to increased competition among species for their survival and reproduction capabilities, which results to the passing on of beneficial traits to subsequent generations. The process of natural selection is mainly determined by the evolutionary fitness of the organism. Genetic drift is also another mechanism for change that takes place when there is a change in the allele frequency in successive generations mainly due to sampling errors. An outcome of this is that the selective force are either weak or absent resulting to a drift in the allele frequencies in a random manner that can either be upwards or downwards. The random drift in the allele frequency stops when the allele is finally fixed due to its disappearance from the population or an entire replacement of other alleles. This implies that genetic drift has the potential of eliminating certain alleles from a population basing on chance alone. Even in cases whereby there are no selective forces, genetic drift has the probability of causing two separate populations that started with a single genetic makeup to drift apart resulting to divergent populations of species having dissimilar sets of alleles. Horizontal gene transfer that takes place between different species and populations can also result to the evolution and the formation of new species.The fundamental theory of evolution is based on the fact that there is possibility of the DNA of a living species to transform or mutate. Mutation usually imposes effects on the DNA that are transmitted to the offspring either immediately or after a number of subsequent generations. The change in the DNA structure due to mutation can be beneficial, harmful or have no effects on the species. In cases whereby the mutation is harmful, there is a probability that the offspring of the species is likely to survive and reproduce, as a result, the mutation usually dies out. In cases whereby the mutation is beneficial to the organization, there is a probability that the offspring will reproduce, resulting to a survival of the mutation. During the course of reproduction, there is the wide distribution of the beneficial mutation. The process through which bad mutations are cut out and beneficial mutations are spread is referred to as natural selection. As the mutations take place and are distributed over time, they result to the formation of new species. In the course of millions of years, mutations and natural selections have played an integral role in the creation of the various forms of species that are present today. This is the basis of the evolutionary process, during billions of years ago, there was a random organization of chemicals that resulted to the formation of self-replicating molecule. This served as the origin of the various life forms that are available today and those that are already extinct such as the dinosaurs. Mutation and natural selection resulted to the subsequent development of other forms of life from the simplest self-replication organism.Chapter 21: Viruses and ProkaryotesCells are considered as the basic units of structure and the way through which they obtain their energy. As a result, cells are grouped as either prokaryotes or eukaryotes. The six classifications of living organisms is mainly determined by the structure, and in the context of prokaryotes, it includes the kingdoms of Monera and Archaea. Prokaryotes are basically molecules that are enclosed in a cell membrane and cell wall. This is in contrast with the eukaryotic cells that have organelles. Prokaryotic cells also have photosynthetic pigments and a whip-like flagella that is used for the locomotive purposes and adhesion. Another characteristic of prokaryotic cells is that they are found in diverse shapes including cocci, bacilli and spirrila. Prokaryotes generally lack the cell nucleus and other organelles that are enclosed within the cell membrane. The DNA information of prokaryotic cells is not contained within the membrane and it is not distinguished from the rest of the cell; rather, it is coiled in the plastoplasm and usually referred to as the nucleoid. The structure of prokaryotes contain capsules, which is an extra external covering that serves to protect the cell in cases where by it has been engulfed by other organisms. The capsules are also vital in retaining moisture for the cells and helps in the adherence of surfaces and nutrients. Prokaryotic cells also have a cell wall that is used in the protection of the bacterial cell. The cytoplasm comprises of water and other enzymes. The cell membrane on the other hand has a role of regulating the flow of substances entering and living the cell. Pili are hair-like structures that are used for attachment to other cells and surfaces. Protein production is undertaken by the ribosome while the plasmids are used in carrying genetic material.Reproduction within the prokaryote cells take place asexually through binary fission, whereby there is replication of the single DNA molecule and the original prokaryotic cells is disintegrated into two similar cells. Binary fission usually starts with one DNA molecule that replicates and all the copies attach themselves on the membrane of the cell. A cell membrane then grows in between the DNA molecules and pinches inward when the bacterium doubles its size. A cell wall is formed to differentiate the DNA molecules and divides the bacterium into daughter cells that are identical.The cell wall serves as the target for most of the antibiotics and the carbohydrates that the human immune system deploys to detect infection. The potential threat to the existence of human kind is that bacteria are increasingly evolving to become resistant to the antibiotics, something which can be attributed to overuse of the antibiotics.Viruses on the other hand can be described as the genetic information that is usually enclosed by a protein coat. Viruses may have external structures and cell membrane. They are usually considered as intracellular parasites, implying that they need host cells so as to have the ability to reproduce. In the lifecycle of viruses, a virus usually infects a cell, which in turn allows the genetic information of the virus redirect the creation of other virus particles by the host cell.The structure of viruses is characterized with a number of different shapes and sizes, usually referred to as morphologies. Viruses are relatively smaller when compared to bacterial cells and have a diameter of approximately 20-300 nanometers. A virus particle has nucleic acid that is enclosed within a protective coat referred to as the caspid, which are created from protein subunits that are similar referred to as capsometers. The shapes of the viruses can be helical, icasahedral, prolate, envelope and compex.Reproduction in viral cells does not place through the process of cell division owing to their acellular structure. This implies that viruses rely on the machinery and the metabolic functions of the host cells to increase their populations, which is achieved when they assemble within the host cell. The viral lifecycle varies significantly among the various species although there are 6 fundamental steps of the viral lifecycle including attachment, penetration, uncoating, replication, self-assembly and release from the host cells. Attachment entails the binding of the viral caspid protects with particular receptors that ate found with the cellular surface of the host. After attachment to the host, penetration takes place whereby the viral cells enter the cells of the host using membrane fusion or endocytosis that is mediated by the receptor. This phase is usually refered to as viral entry. Uncoating entails the removal of the viral caspid through degeneration and simple dissociation. The outcome of this phase is the release of the genomic nucleic acid by the viral cell. Replication entails genome multiplication and entails the synthesis of a viral messenger. The release of the viral cells from the host takes place through lysis.