Darwin preferred the term natural selection to explain his model of evolution due to the variations in the rates of reproduction exposed by dissimilar variants in the population.
The theory of evolution by natural selection can be summarized into three principles and are as follows:
i. Principle of variation – between the individuals within any population, there is a difference in morphology, physiology and behavior. For instance, the organisms within the population show individual differences like body size, hair color, voice properties, and facial markings etc. In contrast, some traits exhibit little or no difference among individuals such as number of eyes in vertebrates.
ii. Principle of heredity – Offspring look like their parents than they resemble irrelevant individuals. Because some traits are constantly passed on from parent to offspring. Such characters are heritable, other characters are powerfully influenced by environmental conditions and exhibit weak heritability.
iii. Principle of selection – several kinds are more successful at existing and reproducing than other forms in a known environment. Individuals having characters well suitable for the fight for limited resources will exist more and reproduce above others and hence contribute more offspring to the next generation.