Over a number of generations, adaptations take place through successful combination of small, random alterations in traits, as well as natural selection of the changes best suited for a particular environment. Genetic drift on the other hand results in production of random alterations in the number of characteristics in a population. Genetic drift occurs as a result of the role played by chance in determining whether an individual will live on and reproduce (Starr, Taggart, and Starr p, 415). The greatest controversies of biology are found in the unity and diversity of life.
Naturalists have greatly employed Darwins explanation of unity or organic forms in order to resolve this controversy. Darwin applied the concept of evolution to every living thing including human beings, and claimed that all individuals, who belong to the same species, reveal some sort of variation between them (Goodenough, Wallace, and McGuire p, 9). According to Darwin, individuals who have advantageous features, for both reproduction and survival, pass them down through genetic inheritance from one generation to the other.
Darwin teaches that variation, on which natural selection plays a role, is basically of small magnitude and that indefinite variation in all directions as well as the progressive accumulation of a particular series of variations, all resulting in the production of a novel species, occurs as a result of natural selection (Gulick, 28). In his theory of natural selection, Darwin stated that only those organisms that have the advantageous characteristics that suit a particular environmental condition are selected by nature.
Natural selection, therefore, turns out to be a vital aspect in the evolution process (Darwin p, 45). Unity and diversity of life comprises of the dual facets of life on earth. Natural selection gives an account of the relatedness among organisms in a population by revelation that different animal species are related through descent from a common ancestor (Gulick p, 25). Modern animals, including man, are believed to have originated from a common simple ancestor.
However, as a result of increased complexity, modern species appear different from the ancestral species. Nevertheless, a remarkable evidence of unity of life is revealed by the similarities in the molecular structure of species. Modern molecular studies reveal biochemical similarities between different species. Comparison of DNA sequences between human beings and apes reveal a close genetic similarity. This reveals that these two species probably had a common ancestor (Starr, Taggart, and Starr p, 410).
Natural selection also gives an account of the great diversity that is displayed by modern species. Organisms that have distinct traits that enable them to live in environmental niches not occupied by similar organisms, according to Starr, Taggart and Starr, possess a greater chance of surviving (p, 410). Over generations, species which originated from a common ancestor have diversified in addition to occupying more and more environmental niches in order to take advantage of unutilized resources.
Modern species are a phase in the progression of evolution, and their diversity results in the development of a series of speciation as well as extinction. Diversity of life, according to Gulick, does not result in development of a completely new and unique organism, but rather in organisms that share certain morphological similarities (p, 27). Vestigial characteristics that have no specific role resemble functional ancestral characteristics, and as a result, organisms can be categorized using these similarities into a ladder of connected groups.
Work cited: Darwin, Charles. Natural Selection: The Global Struggle for Existence, ISBN 1565430824: Lulu. com, 2008 Goodenough, Judith. Wallace, Robert. and McGuire, Betty. Human biology: personal, environmental, and social concerns, ISBN 0030012813: Saunders College Pub. , 1998 Gulick, John. Evolution, Racial and Habitual, Controlled by Segregation, ISBN 1115895672 BiblioBazaar, LLC, 2009 Starr, Cecie. Taggart, Ralph. and Starr, Lisa. Biology: the unity and diversity of life, 10th edn, ISBN 0534388000: Thomson Brooks/Cole, 2004