Natural Selection

Introduction

Natural selection is the process through which evolutionary changes occur in living things over an extensive period. According to Darwin‘s theory of evolution, the organisms that are well adapted to their environments survive better and pass down their genes to their offspring’s (Williams, 2008). As the process repeats over millions of years, the less fit organisms become extinct while the better organisms live. Within each species, more individuals are produced than can be supported by nature’s limited resources. Therefore, the organisms struggle naturally for survival with the available resources. There are many spontaneous variations within each species. Some of the variations allow organisms to survive better as they are useful for adaptation to the environmental conditions. The organisms with these adaptive variations survive to the next generation and pass their genes to their offspring. Darwin and Wallace viewed the variations arising by chance.

Discussion

Population genetics use the gene pool to study variations within a population modern biologists view each individual as a single vessel hosting a fraction of the gene pool, which is a fraction of the total population’s genetic variation (Hartl & Clark, 1997). Population genetics is concerned with the variations existing between communities of reproducing individuals within a local population. The one gene model of population genetics postulates that each of the species has a set of genetic loci that influence the development of a particular trait. It assumes that an individual has a single locus, with only two allelic expressions. Hardy-Weinberg discovered that allelic and genotype frequencies characterizing a population do not change from generation to generation in sexually reproducing populations, if some conditions remain constant. The population remains stasis if the alleles at a locus are stable (no mutations), neutral (no selection occurs in favor of one allele), the population is effectively closed (no migration) and finally if the population is infinitely large and panmatic.

Microevolution refers to genetic change over time, through changes in allelic frequencies within a single population between successive generations. According to this theory, the process of evolution occurs whenever there are changes in hardy-Weinberg law during mutation, relocation, genetic drifts and the process of natural selection. These theories relate to the original Darwin- Wallace model as they describe the evolution as changes in allelic frequencies, in a gene pool, between successive generations. A population is genetically stable over time, and evolution only occurs when the genetic equilibrium is disturbed.

Punctuated equilibrium suggests that Darwin’s theory of evolution is wrong since the process of evolution occurs as rapid bursts. It predicts the process of evolution occurs very fast tied to speciation events. Speciation takes place in two major ways. The first way occurs when a single species changes over time to a new species through the process of anagenesis. The second is the sympatric speciation process where a population of species sharing the same ecological habitat becomes reproductively isolated from each other. This process occurs through processes such as polyploidy. A small population remains isolated with distinct selection, through rapid environmental changes. Genetic drift influences the process of evolution based on the model of peripatric speciation. In this case, there are no fossils representing transitional forms due to relatively small size and the rapid changes in their isolated ecological niches. Similar to Darwin’s theory of evolution, there is gradual non-punctuated evolution in the fossil records.

Conclusion

Natural selection is significant in modern biology because it is analogous to artificial selection process used by breeders to select plants or animals with desirable traits for breeding. The interaction between the concepts of natural selection coined by Darwin’s evolutionary model with discoveries in molecular genetics has led to the development of further theories. However, natural selection remains the primary rationalization for adaptive evolution. The impact of the Darwin –Wallace model is huge as it brought two major contributions to the scientific world. The model provided carefully organized biological data to support their theories and a clear explainable mechanism of natural selection through which the process of evolution operates.

References

Williams, G. C. (2008). Adaptation and natural selection: a critique of some current evolutionary thoughts. Princetons University Press.

Hartl, D. L., & Clark, A. G. (1997). Principles of population genetics (Vol. 116). Sunderland: Sinauer associates.