Introduction
Dissimilarities and similarities among different groups of organisms are the result evolution. This change occurs in the characteristics of different biological populations with the passage of time. The four forces of evolution result in speciation. Speciation is the process in evolution through which new species arise. It could result from any of the four forces of evolution. These are genetic drift, mutation, gene flow, and selection. They lead to slight changes in existing species, as well as the formation of new species.
Mutations
This is the main source of evolutionary change. It occurs randomly, when mistakes take place in copying during cell division. It could involve changes in single bases of DNA, or even the relocation of entire chromosomes. For species that reproduce sexually, only the mutations that take place in the sex cells have evolutionary consequences, which affect future generations. Mutation is very rare, occurring on about 30 mutations in a million. It may also be caused by environmental factors such as exposure to radiation, certain dyes, preservatives and antibiotics.
Mutations result in changes in the DNA of an organism, and this can affect all aspects of the life of the organism, from its appearance, it behavior and even its basic physiology. This leads to variations within a species. The term variation refers to genetic diversities within a given species. Most mutations that occur are neutral, being neither harmful nor beneficial. However, some forms of mutation can be very harmful, leading even to death. An example of this is cancer. Others may serve useful purposes in a population. For example, sickle cell anemia is common in places prone to malaria. Although it is harmful to the individual, it is useful in the sense that it destroys malaria parasites. This is one beneficial form of mutation. Mutations ensure continued evolution.
Gene flow
This is the introduction of other new variants of genes from the nearby populations to the other populations. This prevents speciation. Individuals emigrating from small populations may take with them novel alleles. The genes are transported from a given population to the other. An example of this is pollen being blown from one region to a place where it did not exist previously.
The addition or loss of members of a particular species can easily lead to changes in gene pool frequencies. This can happen even if no other mechanism of evolution is operational. For example, if every red haired person were to move out of Scotland, the generation that follows would be very likely to have very such traits within the population. This would be a form of evolution among the Scottish population. The populations, which red haired people moved into, would also evolve to have very large numbers of people with red hair.
In some cases, gene flow can flow between species. For example, segments of DNA could be transferred from a particular species to another species by viruses in the process of invading the cells of plants or animals. This is a very rare type of gene flow and occurs in very small proportions within any given population.
Genetic drift
This is chance fluctuation in the frequency of alleles within the gene pool of a given population. It is the effect of randomly occurring events on a small population’s gene pool. It is believed to have influenced human evolution, because in the past, human beings lived in small and isolated populations. It is also a random process. Allele frequencies change within a small population because of random events. An example of this is lightning starting a fire in the forest, which kills more brown-eyed squirrels than blue-eyed squirrels, leading to an increase in their numbers. This can lead to variations within a population, where different organisms belonging to the same species in a given population have certain differences. It can also lead to variations between populations, where the organisms found in a given population differ from those belonging to another population.
Human beings are not affected by genetic drift due to their large numbers. However, accidents in small populations could alter the allele frequencies in the gene pool, leading to certain changes within the population. Founder’s effect could occur when a population is divided into two populations or more, where one of the groups has certain differences from the main group. It could lead to the formation of a new population, which is different from the original larger one. Founder’s effect is responsible for the limited variability found in isolated islands.
Natural Selection
This is the force of evolution responsible for adaptive change. It reduces the allele frequency of maladaptive or harmful traits within a given population and increases the occurrence of alleles bearing adaptive traits. An example of this is the body types of people from different climatic conditions. The people living in cold areas tend to be short and stout while those in hot areas tend to be lean and tall. This makes it easier for them to cope with the climatic conditions.
In natural selection, nature selects the individuals that are best adapted and they produce the largest number of offspring. These offspring in turn carry onward to their own offspring the genes, which gave their biological parents the upper hand in evolution.
Natural selection place within populations, and different members contribute different proportions of their genes to the subsequent generation. This leads to changes in the proportion of alleles in the generations that follow, leading to changes within that population. The offspring of each generation is superior to its predecessors. This is biological evolution.
Definition of Terms
The term population refers to the summation of all organisms belonging to the same group (species), living in the same geographical location, and having the ability to interbreed. The term species refers to a group of organisms, which are able to interbreed and produce viable offspring.
Speciation is the process through which new species are formed. It can take place in a branching fashion (this is known as cladogenesis) or without branching, (this is known as anagenesis). A population accumulates enough new mutations as time goes by until it can eventually be considered a different species.
Conclusion
Evolution is controlled by some isolation mechanisms. The term isolating mechanisms refers to the reproductive characteristics that prevent different species from fusing. They are especially important in the concept of biological species, in which the different species of sexual organisms remain defined by their reproductive isolation, that is, a lack of genetic mixture. There are two main types of isolating mechanisms between different species. They are pre-mating and post-mating isolating mechanisms. It ensures that animals belonging to different species do not reproduce, thus controlling evolution.
