Darwinism

Achievements of Darwin

 Charles Darwin while on voyage abroad "The HMS Beagle (ship)" made observation about the great variety of birds and reptiles on Galapagos Island and their relationship to similar groups on the Ecuadorian mainland.

Charles Darwin

Charles Darwin was greatly inspired by the work of his geologist friend Charles Lyell whose major thesis was that geological forces produce a constant changing environment. Darwin also came across by a clergyman and an economist Thomas Malthus, who maintained that human population tend to increase at a much greater than does the food supply necessary to sustain the population. 
Darwin studied an essay outlining a similar theory of evolution by another naturalist, Alfred Russel Wallace, who observed diversity in plants and animals and their peculiar distribution in South America, Malaya and Indian archi-pel-ago. He also knew about the practices of plants and animal breeders producing in a new generation, the desired traits in domestic animals and plants by selective breeding. All the above knowledge helped Charles Darwin, to propose a theory of evolution by natural selection, he proposed his theory at a scientific meeting of Linnean Society in London in 1858 and published his famous book, named "The origin of species by means of natural selection" in 1859. The salient features of Darwin's theory of evolution : 

 Over production 

All organisms tend to reproduce in geometrical progression (1,2,4,8, ,2n).It means organisms multiply very rapidly. If all the organisms produced remain alive would result in Million of organisms of a single species on earth in a matter of a century even in case of slow breeders, such as elephants. One bacteria can produce two million ton bacteria within 24 hours.

 Heritable Variations

Darwin noticed that all the individual of a species are not alike at the time of birth. He realized that some of the variations were useful for the individuals as they carry them comfortably to live in that environment. These individuals could adapt to their environment more than the individuals which did not possess these useful variations. Competition for Survival: The available resources of the environment such as food, water, shelter, etc. are limited. Food can increase in arithmetic fashion (1,2,4,6,8,10,......). It means food can be increased slowly. 
We have seen that population of organisms increases in geometric progression (2n). Therefore the ratio of organisms to food reach unmanageable proportion and leads to a struggle for survival. The individuals of a species compete with each other and with the individuals of other species to get their food. 

Natural Selection:

 In the competition for survival and struggle for existence the individuals that are better adapted to the environment are successful and continue to produce 'offspring with their adaptive characteristics. The characteristics which provide adaptiveness or fitness come to accumulate in the population than those characteristics which decrease fitness.
 The greater reproductive success of the better adapted from constitute the natural selection. 
Explanation of Darwinism with Example
 According to Darwin the ancestors of modern giraffe's had various lengths of necks, some had long and some had short necks. The long necked giraffes were able to eat the leaves of the trees as well as grass. 

Ancestor's of modern giraffe

When the grass became short, the long necked giraffe could obtain more food from the top of trees than short-necked giraffe and were more likely to survive and reproduce. This favourable variation of long neck was inherited by offspring generation after generation. The present long necked giraffe is the result of this type of evolution. Modification The theory of evolution proposed by Darwin has been modified in the light of modern evidence from genetics, molecular biology, paleontology, ecology and ethology (the study of behavior) and is known as neo Darwinism or synthetic theory of evolution.