Charles Darwin and another scientist Wallace worked together and in 1858, Darwin published his famous book The Origin of Species by means of ‘Natural Selection’. In his book, he proposed the theory of evolution. The theory explains the origin of species and hence the evolution. Followings were the main postulates of the theory:
- Struggle for existence
- Survival of the fittest or natural selection
- Structural modification
- OVER PRODUCTION
Darwin pointed out that all the living organisms have a high rate of reproduction. Each and every living organism produces more individuals that can survive. For example, the codfish lays 5-7 million eggs and if all eggs developed into fish then oceans of the world would soon be chocked with codfish only. Another example is that the elephant is the slowest breeder. It reaches reproductive age at 30 and continues to produce off springs till the age of 90. During this period, a single female produces six young ones. Darwin concludes that after a period of 750 years, a single pair of elephant can produce nineteen million descendents.
- STRUGGLE FOR EXISTANCE:
The tendency of organisms to produce greater number of offspring than the number of organisms that can possibly survive in severe competition for food, for space, and other essentials of life; this struggle is known as the struggle for existence. There are three types of this struggle
- Interspecific Struggle: It is the competition between different species to get available benefits.
- Intraspecific struggle: It is the competition between the members of the same species. It is much more fierce and dangerous than interspecific struggle.
- Environmental struggle: it is the struggle of survival against the catastrophes, seasonal changes, environmental horrors and climatic factors.
Organisms of the same species are not completely similar to each other; instead, they are slightly different; this is called variation.
- NATURAL SELECTION or SURVIVAL OF THE FITTEST:
Some species possess more useful variations and characteristics. Such species are better adaptive to their environment than others are. This individual advancement, by Darwin, is called the survival of the fittest or natural selection.
- STRUCTURAL MODIFIUVATIONS:
Individual with usual variations i.e. fittest live to maturity and transmit their favorable variations its off springs. The selective process continues generation to generation and in the course of a very long time, these favorable variations accumulate to such an extent that a new specie is modified. This is called origin of species. Hence the gist of Darwin theory is;