Evolution involves a series of changes transforming plants and animals to their present states from their original and simplest states. The present state of plants and animal can be described as complex. The changes take place continuously over many generations. The evolutionary changes exhibited in plants and animals are genetic features and traits that have been continuously passed down from the original generation to the present one. The current state of plants and animals represents only a phase of the never-ending transitioning process. The evolution process has four forces: Mutation, natural selection, genetic drift, and gene flow. Isolation of populations causes evolution that in turn leads to variation and lastly speciation.

Mutation as one of the four forces of evolution is the permanent and sudden change in the features of the gene of an organism resulting in new characteristics that are inherited on to the next generation. The hereditary material called DNA contains the gene. The function of the DNA is to determine the size, behavior, shape and the whole of a particular organism. Any variation in the DNA results in the change of character of the gene that also leads to great changes in every aspect of the life of the organism. Mutation is regarded as one of the forces of evolution because of the transmitting of the mutated gene to the offspring of an organism and eventually to the next generation. On the other hand, all mutations do not necessarily result in an evolution. There are some mutations that take place in the non-reproductive cells of an organism. Such kind of mutations are transferred to the offspring. Germ line mutations are the only type of mutations that occur in the reproductive cells and only transmitted to the offspring resulting in evolution. Mutation is the ultimate source of change in evolution.

Natural selection is a mechanism by which some genetic characteristics become either more or less dominant within a particular population. A population is a representation of less or more separate organisms that belong to the same group within a species. Members of the population are restricted to mate with other members of the population only. Geographical and social factors restrict the reproduction of members of a population with members of other population. The physical traits or the phenotype are the only affected traits by natural selection. The members of a small population can share the same genetic traits due to inbreeding that occurs in generations. However, genotype determines the phenotype or the physical traits. In the process of natural selection, some traits disappear and are not transferred on to the next generation, while some physical traits become dominant in the population.

Species is a composition of the largest natural populations of every living organisms with the ability to reproduce and breed. According to anthropologists, members of a species can be described to be reproductively isolated from other members that belong to every other species. Members of the same species are grouped together according to the similarities they exhibit. The appearance of new species can occur when a population is separated, and interbreeding is not possible. The process is called isolation mechanism. Isolation mechanisms prevents the flow of gene between populations initiating random mutation to effect the original population only. This results to the formation of new species or speciation. The separation of two populations for a significant amount of time results in the members not recognizing each other, thus a new species is formed. Variation is important for organisms because it helps them to adapt with the ever changing environment. Therefore, variation ensures that an existing population is not wiped out in an event that the environment changes.

Gene flow is also known as gene migration. It is the process of transferring gene from one population to another as result the genetic composition of the new population is altered. Gene flow occurs as a result of dispersal and immigration. For example, it takes place when a pollen is blown from its original location to a new destination or when individuals move from their original population to a new population. Genetic variation results when the newcomers carry distinct genes to a new population and interbreed with the population’s members. This activity plays a vital role in the process of evolution. Therefore, gene flow is considered as one of the forces of evolution.

Genetic drift also known as allelic drift is the change in number or frequency of a gene in a population. The process takes place over time by random processes or by chance. The genetic composition of the population is affected by genetic drift. It also affects the genetic composition of the next generation hence affecting the evolution process.

The four forces of evolution have actively played a big part in the evolution of animals and plants for many generations and also for several years to come. The forces will continue to determine the evolution process of the subsequent generations from their ancestors. From the discussion, natural selection can be said as the major force of evolution. However, the other three forces of evolution influence the process of natural selection.