Evolution is the progressive alteration in the inherited features of a biological population. The progressive change, gives rise to diversity at the various stages of biological organization, these stages are namely molecules, species and individual organisms. A biological population is a group of organisms that share a common gene pool, hence they can interbreed between each other, and they live in the same geographical area (Karleskint et al. 25). A gene pool is sum total genetic information on any population of a specific species while, species is a group of organisms that can interbreed to produce a fertile offspring (Brock 13).
Macroevolution is the phenomenon of evolution taking place in a range of separated gene pools. Macroevolution concentrates on the changes at a specific level of species or above that level. Microevolution on the other hand is genetic change of a smaller scale that takes place within a population or species (Cooley 125). Macroevolution gives attention to the grand changes and trends in evolution, which are generally the history of life (Campbell 29). The history of macroevolution is not easy to observe, this history is reconstructed using available evidence such as geology, living organisms, and fossils. It is through the evidence that is available for the reconstruction of the history of life that answers on how the history of like took place. Macroevolution can be viewed as the collective effect of microevolution.
Microevolution takes place through the mechanisms of migration, natural selection, mutation, and genetic drift (Cooley 125).Gene flow or migration, takes place when genes are transferred from a population to another one. Natural selection, the mechanism by which organisms that adapt optimally have a higher chance of producing the most offspring and hence the genes of the optimally adapted organisms are transferred to their offspring. Mutations are unsystematic changes in the DNA sequence of an organism, which can lead to various changes in an organism’s physiology or behavior. Genetic drift is the mechanism by which probability has the role in deciding which genes variants or alleles will carry on with the offspring. Microevolution gives attention to the alterations of population allele frequencies (Haviland 47).
Genetic variation is caused by mutation. Variation can occur among several populations that are at different geographical locations or within a single population. Variation is caused by mutation, which is a permanent chemical change in DNA structure, or Gene flow, which is the movement of genes from one population to another population or lastly, through Sex, whereby a new gene combination is introduced into a population, in the case genetic variation is the result of gene shuffling (Wright & Hastie 59).
Speciation is the progression by which new species come to existence, through lineage splitting events. Speciation is caused by geographic isolation. Geographic isolation is the physical separation of organisms that were previously in the same population after a change in habitat such as continental drifting, a change in river course, or mountain formation. After separation, the separated populations no longer have contact with each other and therefore they no longer mate. Speciation takes place when the separated populations live apart for a long period until they can no longer produce a viable offspring because of mutation (Haviland 47). Another cause of speciation is gene flow whereby a population may grow in a vast manner such that organisms at the far ends have a minimal chance of mating. In this case, different selective pressures are needed at the different ends, which would change the gene frequencies, such that the organisms would no longer be able to mate if reunited. Macroevolution focuses on speciation (Haviland 47).
Brock, James P. The Evolution of Adaptive Systems. San Diego, Calif: Academic. Academic Press. 2000. Print.
Campbell, John H. Creative Evolution?!: [proceedings of a Symposium at the University of California, Losangeles, in March, 1993]. Boston u.a: Jones and Bartlett. 1994. Print.
Cooley, Dennis R. Technology, Transgenics and a Practical Moral Code. Dordrecht: Springer. 2010. Print.
Haviland, William A. The Essence of Anthropology. Belmont, CA: Wadsworth/Cengage Learning. 2012. Print.
Karleskint, George, Richard Turner, & James Small. Introduction to Marine Biology. Pacific Grove, Calif: Brooks/Cole.2010. Print.
Wright, Alan F, and Nicholas Hastie. Genes and Common Diseases. Cambridge: Cambridge University Press. 2007. Print.