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1 Charles Darwin Abstract As early as 6th century BC, the concept of evolution existed. However there was lack of valid explanations to show why species evolved. Charles Darwin contributed greatly in the evolution by proposing the natural selection theory. The theory is based on competition for the limited resources, avoidance of predators, and the ability to attract a reproduction mate. The individual possessing the best traits is able to survive and pass their traits to offspring.

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2 Darwin’s scientific discovery remains the foundation of biology as it gives a logical explanation of the life diversity. After completing his theology course from the Cambridge University, he took up a position as unpaid naturalist on a ship to survey the fauna and flora in the islands of Galapagos. He studied the organisms while there and observed that they slightly differed from those of the American mainland. He inferred that the variations were as a result of the different ecological niches they occupied and concluded that they had a common ancestry. This assay demonstrates Darwin’s contribution to the field of evolution, as well as the impacts of his research.

3 Charles Darwin Introduction Charles Darwin was an English naturalist who greatly influenced the knowledge of life on earth through his theory of natural selection. He was born on 12th February 1809 in Shrewsbury and died on 19th April 1882. Darwin was interested in all living things while young.

He read many books that touched on geology and biology and also collected plant and animal specimens. He went to the University of Edinburgh in 1885 for medical studies but dropped the course after two years. He later on joined Cambridge University in 1828 and graduated with a degree in theology in 1831. Having graduated, he took a position in H.M.S Beagle surveying ship as a volunteer naturalist for five years (Wyne, 2002).

While on voyage to South American and Australian waters, he made a collection of many plant and animal specimens which he observed and studied and laid the foundation of his theory.

He continued with his nature studies on returning to England and in 1844, he started to put together his great ideas in a book called the Origin of Species. In the book, he hypothesized the natural selection theory explaining that life is a continuous struggle for existence whereby only the fittest survives. At this time he also found out that Alfred Russel Wallace (1823-1913) had a similar opinion. Wallace had proposed similar ideas in a paper called “On the Tendency of Varieties to Depart Independently from the Original Type” (Wyne, 2002). They presented their work together in 1858 at a meeting of the Linnaean Society of London. His book, Origin of Species, was published in 1859 and he continued to write on botany, geology, taxonomy, paleontology and zoology until his death.

Why Darwin?

4 As a biologist, I am more interested with studying the life of living organisms. There is a wide variety of living organisms in this world and evolution as a major topic in biology helps me to understand the variety of life better. Evolution enhances the understanding of the life changes and developments as it helps explain the great variations of life. Charles Darwin’s theory of natural selection forms the basis of evolution. Darwin accounted for the great variation of life by proposing the idea of common descent, and the natural selection mechanism. Darwin collected massive evidence to formulate and support his theory on evolution. He was therefore central to the redefinition of evolution, which is the foundation of modern biology (Starr et al., 2008).

Darwin’s Contribution to Evolution The theory of natural selection integrated life sciences by postulating that all living things have the same ancestry and the variations existing result from the colonization of different environment.

“His theory reconciled a host of diverse kinds of evidence such as the progressive nature of fossil forms in the geological record, the geographical distribution of species, recapitulative appearances in embryology, homologous structures, vestigial organs and nesting taxonomic relationships. No other explanation before or since has made sense of these facts” (Wyne, 2002, para 1).

His theory of evolution helped to explain the variations in the population attributing it to competition for the limited resources, reproduction of offspring, genetics, and natural selection whereby those organisms with most favorable traits are able to survive and reproduce. He postulated that the changes in the population are subtle and occur over a long time. The present day species differ from those that lived long time ago and the species differ slightly in form or behavior according to geographic zones. He supported this hypothesis using fossil records (Darwin & Levine, 2003).

5 Darwin observed that speciation in a population with the same ancestor occur over time.

The similarities observed in organisms that are grouped together are because of the traits that are inherited from the common ancestor. Since there was no proper explanation for the sudden appearance of new forms of organisms and the continued variation of organisms in fossil records, Darwin proposed evolution as being a gradual process. He summed up the above arguments in the process of natural selection (Starr et al., 2008).

Natural selection is anchored on variation, inheritance, high fertility rate and the ability of organisms to survive and reproduce. The competition for the limited resources will advantage individuals with variations that are better suited. These results to change in frequency of traits in the population as well adapted organisms are selected. The traits for natural selection must be heritable and confer a competitive advantage (Darwin & Levine, 2003).

Importance of Darwin’s contribution Darwin’s theory of natural selection has been integrated with genetics to advance the field of evolution. The survival and reproduction of certain genotypes and their related phenotypes can be explained by the natural selection mechanism. Variations in a population arise by chance through a change in the genetic code. Natural selection operates on these existing variations within the population, (Wyne, 2002). It is widely known nowadays that evolution involves a change in genetic constitution of a population. Natural selection makes individuals well adapted to pass on their genes to the subsequent generation. Thus natural selection regulates the gene frequency as it favors well adapted individuals.

Natural selection provides explanations for the many variations existing in populations.

For example, it has been used to explain the evolutionary change of moths. Before the industrial revolution, the peppered moth, Biston betularia were typically light in pattern. But after

6 industrialization, smoke and effluents from the industries darkened their habitats. The dark morph became abundant as the light morph disappeared from the industrial areas. This is because the dark morphs were able to camouflage from birds (Starr et al., 2008). Thus natural selection forms the basis of the theory of evolution as results to development of adaptive changes. Natural selection can also be demonstrated in the sickle cell trait, which is a genetic defect affecting the structure of the red blood cells. The red blood cells of individuals with this trait have a reduced capacity to carry oxygen. It has been shown that people with sickle cell trait have increased resistance to malaria. A great majority of these individuals are found in malaria endemic areas, especially in Africa (Fisher, 1930).

While on the voyage of the Beagle, Darwin collected and described different animals and plants. He studied the finches on the Galapagos Islands, about 500 miles from the South American mainland, and realized that although they were unique to the islands they were nevertheless related to the species in the mainland. The Galapagos Finches were of 14 species and their bills were modified to specific diets. Each island was inhabited by slightly different species. Through his idea of inheritance, Darwin concluded that Galapagos Island provided isolation that made the finches to differ from those in the mainland, while the conditions on each specific island led to the specific adaptations. He concluded that the formation of new species was as a result of continuous variation, selection and inheritance in isolation (Darwin & Levine, 2003).

Darwin also carried out many breeding, experiments with animals and plants. He studied dispersal and viability of seeds by soaking different seeds in a tub filled with seawater and planting them to assess which ones were viable. He designed his experiments as a further investigation into his theory of natural selection by focusing on inheritance and variation. He

7 bred pigeons in order to understand the creation of new species from a common ancestor by accumulation of small changes over time.

Conclusion While Darwin’s theory of natural selection helped to explain the variations within a single species, there is no proven scientific evidence of any permanent change in species. Within a population, the genetic make up has been shown to be stable, except for genetic defects such as mutation which are more often fatal and usually lead to death. The variations observed in the populations suit different organisms in different seasons. The same variations can also occur in different generations. Thus the variations are adaptations developed to fit in the environment but they are not permanent changes involving the genetic constitution (Ryan, 2002). I therefore disagree with Darwin’s theory that there are new species that are produced from the existing ones. Whatever is observed are adaptations to the changing conditions and the species can change back to their original state once the conditions are back to normal. Natural selection operates within a species, altering the balance of the populations. However, there is no scientific proof that it can cause a natural population undergo genetic change.

8 References Darwin, C., & Levine, G. (2003). The origin of species. New York, NY: Spark Educational Publishing.

Fisher, R., A. (1930). The genetical theory of natural selection. Oxford: Clarendo Press.

Ryan, F. (2002). Darwin's blind spot: evolution beyond natural selection. New York, NY: Houghton Mifflin Harcourt.

Starr, C., Taggart, R., Evers, C., & Starr, L., (2008). Biology: The unity and diversity of life.

Mason, OH: South Western Cengage Learning.

Wyne, J., V. (2002). The complete work of Charles Darwin online. Retrieved 20 January 2012 from http:// darwin-oline.org.uk