Brief Essay on the Darwin’s Theory of Natural Selection

Charles Robert Darwin (1809-1882) an English naturalist is a remarkable figure in the evolutionary history. He was associated with the Christ College, Cambridge where he joined a team of scientists for exploring the world. He undertook a global voyage for a period of five years in a ship H.M.S. Beangle and discovered Galapagos Islands of South America. During the journey Darwin collected flora and fauna from different part of the world. After returning home, he spent nearly 20 years in analysing the collected materials while preparing a theory of natural selection. Darwin received a correspondence from another scientist A.R. Wallace (1958) working on the flora and fana of malyan archipelago. Incident the views of Darwin coincided with that of Wallace and he was prompted to write a book “Origin of species” in which he was vividly explained “Theory of natural selection”. Popularly his theory is known as “Darwinism”.

Darwin’s theory is based on the following fundamental facts:

(1) Over production

(2) Struggle for existence

(3) Variation

(4) Survival of the fittest and

(5) Natural selection

(1) Over Production:

Every plant and animal has a tendency to produce in geometrical progression (Malathian concept). If all the offsprings of an organism survive, then in a few generations the whole earth will be occupied by the individuals of a single species. Some example of over production can be cited as:

i. A bacterium can give rise to millions of new bacteria in a single day it produced by binary fission.

ii. A fern plant produces millions of spores and it all of them germinate and produce new plants, they will cover the earth in few years.

iii. An evening primerose plan produces 118000 seeds per year. In this rate the number will be enormous in few generations.

iv. Elephant is the slowest breeder among animals. In its 100 years life span and 60 years of reproductive capacity, it produces maximum six offsprings. At this rate couple of elephants will produce 15 million elephants in 500 years.

With such extraordinary productivity of living things an effective check upon every species of plant and animal is inevitable. This check was recongnised by Darwin as struggle for existence.

(2) Struggle for existence:

The immense power of reproduction ensures a competition among the offsprings for food, shelter clothing light mating partner and all other necessities of life. This competition is refereed to as struggle for existence which operated in three ways.

i. Intraspecific struggle: It is a struggle between the individual of the same species. This is most severe competition as the needs of all members are same.

ii. Interspecific struggle: The struggle taking place between the different species of living beings is called interspecific struggle. This is very common because some living beings are food for others.

iii. Environmental struggle: It is the struggle of living organisms against the physical environments like cyclone, earth quake, flood, drought, extreme heat and cold etc. the Mesozoic reptile dinosaur became extinct as a result of this environmental struggle.

(3) Variations:

The differences of offsprings from their same species are called variations. These are the most important aspects of evolution. No two individuals were exactly alike. Such variations were of two kinds, some were inheritable while others were not inheritable. Darwin was not aware of the principles of heredity and hence could not explain satisfactory the causes of such variation. Further, the variation may be beneficial, harmful or neutral. The beneficial variations help the organisms to survive while the harmful variations hinder and handicap the organisms for survival. Neutral variations have no role in evolution.

(4) Survival of the fittest:

The organisms with useful variations have an upper hand in the struggle for existence and they come out successful. They win the struggle, survive and propagate the variation to the next generation. Others with harmful variations perish, while variations give rise to new characters, heredity passes them to the next generation.

(5) Natural selection:

According to Darwin nature selects the fittest ones to survive and rejects the unfit ones as a former selects the seeds for the next year’s crop artificially. In nature, only those organisms which are best adapted to a given set of conditions are most likely to survive.

Due to natural selection the organisms with better suitable characters get more chances of reproduction and these with less advantage characters get less chance. In this way, in species advantageous characters are increasingly accumulation generation after generation and disadvantageous characters gradually disappear.

Criticism:

In spite of its world wide acceptance, Darwin’s theory has been subjected to certain objections. There are:

i. The theory explains only the survival of the fittest but not the arrival of the fittest.

ii. Darwin believed in inheritance of acquired characters which has not been proved by genetics.

iii. Darwin did not accept the discourteous or mutations as the basis of evolution.

iv. The theory does not explain the presence of vestigial organs.

v. The theory fails to give reasonable explanation of the process of mimicry.

vi. Darwin’s theory of pangenesis is completely discarded.

On the basis of these objections and other scientific researches it can be said that natural selection is not the only chief cause of evolution. Darwin himself said that, “The natural selection is an important cause of variation but not its sole reason. “Recently the theory has been modified and known as Neo-Darwinism.