Natural Selection

            Natural selection is a process of evolution advanced by Charles Darwin whereby organisms with certain genetic characteristics are more adapted to a certain environment. These organisms have a higher ability to endure in that environment. The special characteristics also enable such organisms to reproduce and increase in number and transmit their characteristics to other organisms. The chances of survival for these organisms are increased by the special traits as compared to those organisms that do not possess these characteristics. In addition, this process ensures that these genetically inheritable characteristics become more or less widespread in an environment. Through natural selection, evolution of organisms is made possible.

Differential Mortality and Differential Fertility

            Natural selection works in different ways including differential mortality and differential fertility. Differential mortality is the rate at which organisms under their reproductive age, get adapted to the environment and have the ability to survive. The differential mortality rate is determined by the possibility of survival for a certain organism depending on the traits they possess. Certain traits increase or decrease the mortality rate among organisms thus affecting the process of natural selection. The natural selection process will only take place if the mortality rate for different for the organisms in a certain environment. On the pother hand, differential fertility is determined after the organisms have passed their reproductive age. Differential fertility determines an organism’s ability to pass its characteristics to the next generation. The different alleles passed on by the surviving individuals determine the traits that will be possessed by the resulting organism. This means that in the natural selection process only the organisms that are best suited to live in a certain environment will survive and reproduce. Differential mortality and differential fertility form the basic concepts of natural selection.

Effects of natural selection on phenotypic traits

            Phenotypic traits are the visible physical characteristics in an organism. These characteristics vary from organism to organism depending on the genes passed on to them by their parents. The environment also determines some of the phenotypic traits possessed by individuals. Natural selection has major effects on the traits possessed by individuals. Firstly, some organisms may have a variation in the genes that result in a certain trait. These different versions of a gene are known as ‘alleles’. In other cases, natural selection may result in the appearance of the same traits in organisms, which exist in the same environment. The variations and similarities that exist in phenotypic traits of different organisms are as a result of natural selection.

The different patterns of selection are divided according to the causes of the selection and their effect on the phenotypes. Directional selection is a process whereby one type of allele is increased to the disadvantage of others. This means that the frequency of the favored allele is increased significantly as compared to the others. Stabilizing selection is a process that favors those alleles that possess the most common characteristics. In this process, alleles with extreme characteristics may decrease rapidly. Disruptive selection is the opposite of stabilizing selection and favors alleles that possess extreme characteristics. Usually these organisms deviate from characteristics that are considered as normal. The effects of this selection are diverse including bimodal distribution of trait values. In addition, balancing selection is the process through which various allele are favored.

Formation of New species through Natural selection

            As advanced by Charles Darwin, natural selection will always result in the survival of those organisms that possess the best traits for survival in a certain environment. The different processes involved in natural selection ensure that the weaker organisms are eliminated from the environment. It is important to note that those animals that survive the process of natural selection are well fitted for survival in that particular environment. When the different traits are passed on to the next generations, the process of evolution continues to take place hence new species. With continuous natural selection, the organisms continue to change and develop into new species.

Reproductive isolating mechanisms

The environment provides a system that prevents the procreation between different species. The mechanisms employed by nature to do this are called reproductive isolating mechanisms. These mechanisms are divided into two broad categories: prezygotic and post zygotic mechanisms. Reproductive isolation is a combination of all the methods and behaviors employed by nature to avert the production of offspring from the mating of different species. In addition, offspring that is produced as a result of crossbreeding of different species are not fertile and cannot reproduce. These barriers maintain the integrity and continuity of a species over time, reducing the possibility of gene flow between individuals of different species. This allows each species characteristics to be uniquely preserved. Geographical isolation is whereby certain species are geographically separated from others. When these species come together, it is difficult for them to produce any offspring.

Examples of Natural Selection

The first example of natural selection in action is the resistance developed by microorganisms to antibiotics. Among their vast numbers, natural populations of bacteria contain considerable variation in their genetic substance, principally as the result of mutations. Most bacteria die quickly when exposed to antibiotics, but some may contain mutations that make them slightly less vulnerable. Depending on the exposure to antibiotics, the individuals may or may not survive the treatment. If the exposure is short-lived, they shall survive and vice versa. When this selective elimination of maladapted individuals from a population occurs, natural selection takes place. These surviving bacteria then reproduce and produce the next generation that has resistance against the antibiotic.

The second example is the development of a dark colored coat by the deer mice that live in sandy areas. The environment that these animals live in has helped them to develop a coat that acts as a camouflage. The gene that helped them to grow this coat was dominant in many of those who survived the hard conditions of the environment. Thos means that this character has become an advantage for those who possess. They can survive and adapt rapidly to the environment they live in.




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