Darwin’s Theory of Natural Selection (Essay Sample)

Darwin’s Theory of Natural Selection
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DARWINS THEORY OF EVOLUTION BY NATURAL SELECTION
Charles Darwin took interest in natural history while studying for theology degree at Cambridge University. He spent most of his time collecting specimens of living organisms from many parts of the world and making observations. From these observations, he gave an explanation on the origin of plant and animal life forms found here on earth, based on a concept he referred to “Natural Selection”. In his explanation he suggested that;
* Variations occur within members of a population; these variations emerge by chance from within the individual. They are passed on to successive generation through sexual reproduction. Some of the characteristics are advantageous to the individual while others confer limitations.
* In a population, the number of young ones is larger than the number of parental generation but only a small number survive to adulthood and give rise to young ones. Others die young due tp environmental pressure such as competition for food, shelter, mates and shortage of water. The numbers of the population is therefore relatively constant. This shows that competition among members of a population is constant in an attempt to survive, what is called struggle for existence.
* In the struggle for existence, members with advantageous variations are well suited to the environment. They exploit resources, survive and breed in the prevailing environmental conditions. Members with disadvantageous characteristics are poorly adapted; they do not transmit their variations since they die young. This is referred to as survival of the fittest.
According to Darwin, direction of change in an organism is neither controlled by the surrounding nor the individual. It happens by chance. It is by chance that a certain organism is well adapted to a particular environment or environmental changes. Individuals selected for reproduction pass on the variations to their young ones. The stepwise accumulation of small variations from generation to generation over a long period of time leads to emergence of new forms of life
How Darwin’s theory was a major advance over prior ideas as to how organisms changed over time
Lamarck and others had proposed evolutionary theories, they depended on speculation to give explanation on how evolution took place, and there was no evidence. Darwin offered evidence that favored the evolution of plants and animal species. He offered a valid mechanism by which life might evolve. Darwin referred variations as the raw materials for the process of evolution. These variations have now been traced to changes that the gene or chromosomal level. These changes occur randomly and are called mutations. Organisms with advantageous mutations are able to transmit them to their offspring through sexual reproduction. This important since meiosis lead to new recombination while fertilization spreads the gene highly in a population. Transmission of such mutation through many generations could lead to emergence of new species. The emergence of new species requires a long time and is also affected by the rate of mutation that a particular species undergoes. Experimental evidence has shown that most mutations whether advantageous or disadvantageous result in the variation of an already existing structure leading to modification of organs and appendages.
Evidence in support of evolution and the driving forces for evolutionary change
Industrial Melanism
The peppered moth is found in many parts of England and naturally rest on the tree trunks and tree branches. It exists in two varieties; a normal or wild type variety that is speckled white and a mutant variety that is darker. Before industrial revolution almost all the peppered moths were the wild type variety. However since the industrial revolution the numbers of the melanic forms have been increasing steadily in some areas particularly around industrial cities. Fifty years late , about 90% of moth populations in industrial cities such as Manchester were melanic forms. Oppositely the wild forms dominated the rural countryside.
Before industrial revolution, the whole of England was covered with green and fresh vegetation. Due to luxuriant growth of lichens, the trunks and branches of trees were white, the white moth that rested on trees were effectively camouflaged by the white background hence protecting them from being preyed on by birds. After industrial revolution, factories started dumping black soot and other pollutants that darken the trees in areas surrounding the industrial cities.
This proved advantageous for the dark melanic forms, which were now camouflaged by the dark background and thus protected from preying birds. The White wild type moths were easily picked up and eaten by the birds as they