Darwinism:The origin of species by natural selection

In 1831 Darwin got an opportunity to travel on H.M.S. Beagle(a ship in which Charles Darwin sailed around the world) for a voyage of world exploration.The voyage lasted for five year (1831-1836).During this period Darwin explore the fauna and flora of a number of continents and island.Later beagle was sailed to the Galapagos island.Galapagos island consist of 14 main island and numerous smaller island which lie on the equator about 960 km off west coast of south America in the pacific Ocean

Darwin noticed giant tortoises,Metre-long marine and land Iguanas many unusual plants insect, lizard, sea shells and birds on Galapagos island. These giant tortoises may weight as much as 275 kg grow to 183 cm in length and attain an age of 200 to 250 year.

 The principle of Natural selection:

The principal of natural selection stems from five important observation and three inferences which have been mention below

1. Over production(rapid multiplication)

All organism possess enormous fertility. They multiply in geometric ratio. Some example cited below

A cod fish lays several hundred eggs at same time. A female rabbit gives six young one. It assumed that elephant is the slowest breeder;which measures at the age of 30 year and lives for about 90 years. Each female gives rise to about six offspring.

2.Limited food and space:

Despite of rapid multiplication of all types of species, food and space and other resources remain limited. They are not liable to increase.

3. Struggle for existence:

The struggle for existence can be three types.

(A) Intraspecific struggle: 

It is the struggle between the individuals of the same species because there requirements like food, shelter, breeding, places,etc. are similar.

(B) Interspecific struggle:

 It is the struggle between the members of different species. This struggle is normally for food and shelter

(c)Environment struggle:

It is the struggle between the organism and the environmental factors like heavy rain extreme heat or cold,earthquakes,diseases,etc.

 4. Natural selection or survival of the fittest:

The organism which are provided with favourable variation would survive , because they are the fittest to face their surrounding, while unfit are destroyed.It is noted that only survivel od the fittest is not enough. but organism should also adapt or change themeselves according to the environment.

5.Inheritance of useful variations:

The organism after getting fitted to the surroundings transmit their useful variations to the next generation,while non-useful variations are eleminated.

6.Speciation(Formation of new species):

Darwin considered that variation are transmitted to the offspring and appear more prominently in succeeding generation. after some generation these continuous and gradual variations in the possessor would be so distinct that they from a new species.