Evidences from Classification : All the known living animals and plants have been classified into various species, genera, families, order, classes, phyla and kingdoms. The classification of a particular animal is attempted only after its extensive study. It is seen that every living being is related with other living being. The relations may be very close or may be quite apart. On their relationship, they are put under various orders, classes, phyla etc. On the superficial examination one can hardly believe that they are interrelated. But after their careful study they can be arranged in definite order, Protozoa (acellular) being at the base while Chordata at the top. No doubt, there is some sort of gap between chordates and non-chordates today but who known that this gap may be filled some day by some further discoveries. Moreover, the present-day types represent only the terminal twigs of a vast phylogenetic tree and for establishing relationship we should focus our attention on the main trunk. The animals can be classified as described above in a systematic order.

Evidences from Comparative Anatomy : In all the living animals, the basic substance of life is Protoplasm. If the species had been created separately, then there should be no relationship in the various organs and systems of animals. But on the contrary, we see that large number of animals although unlike in appearance show most of the systems and organs made on the same plan. The resemblance are very close in the members of the same group. For example �

(a) Analogy and Homology : While examining the various structures in the bodies of different animals, one may come across certain organs of same origin but of different functions. For example, the forelimbs of salamander, crocodile, bird, bat, whale, and man, all have the same origin and essential structures but different functions to perform. Such structures are called homologous. On the other hand, the wings of insect, pterodactyle, bird and bat perform the same function, though they have different origin and entirely different structures. Such structures are termed analogous.
The homologous structures give us the answer that how the two different types of animals or organs have the same origin and functions to perform; this shows that they have changed themselves according to their different needs.
 Analogous organs are those, which are functionally similar.
 Homologous organs explains divergent evolution.
 Similarity developed in distantly related groups as an adaptation to the same function is called convergent evolution.
 The wings of an insect and a bat exhibit analogy.

If the study of horizontal distribution of animals on the face of this earth is made, it would be seen that animals are not evenly distributed. Two identical places with the same climate and vegetation may not have same sort of animal fauna Alfred Russel Wallace (1823-1913) divided the whole world into six major biogeographical regions or realms. For example, Elephants and Rhinoceros occur in India and Africa only and not in Brazil, although the climatic conditions are alike. Again, members widely separated areas. For example, lung fishes are found in South America, Australia, Africa and nowhere else.

The explanation of this uneven distribution is quite obvious, and can be explained on the basis of organic evolution. A particular species, after arising from one place, migrates to other far off places. While doing so, it has to come across various climatic changes for which it tries to modify it self. In this way, the new species are added. After its dispersal, if some barriers arise, the species becomes confined to that particular region and is isolated from the parent species. This provides a very interesting theory on the mechanism of organic evolution.

Charles Darwin during his voyage around the world studied the fauna and flora of Galapagos islands (off the west coast of south America). Galapagos islands are called 'a living laboratory of evolution'. Darwin studies 20 related varieties of the bird belonging to family Geospizidae different in shape and size of beak. These birds are now called 'Darwin's finches'.

Evidences from Genetics : Johan Gregor Mendel in 1866 published his work on experimental breeding. He bred two individuals differing in certain well-defined characters, and observed the ratio in which various contrasting parental characters appeared in successive generations. Since then, selective breeding has started in the case of domestic animals and plants to obtain the evidences of organic evolution. These furnish the direct evidences of evolution.
Conclusion : According to the above description, we have seen certain evidences in favour of organic evolution. Although the evidences are indirect, merely interpretations based on certain phenomenon, certain organs, systems and other facts but they throw enough light to show us that the present day forms of life have originated from simpler forms in millions and millions of years. The process was continuous gradual, and accompanied by trial and error.
 Recapitulation theory is given by E. Haeckel.
(a) Atavism : Atavism or reversion is the sudden reappearance of some ancestral features. Such as Large canines, thick body hairs, short temporary tails.

(b) Protective resemblance :
(1) A close resemblance with environment for defence and offence is found in many insects.
(2) Some organisms resemble other organisms and thus escape from enemies. This phenomenon is known as 'mimicry'.
(3) Phyllium is the leaf-insect because it resembles leaves. It is an example of mimicry or protective colouration.
(4) Peppered moth, Biston betularia, is found abundantly in industrial cities of Britain.
(5) The change of the lighter coloured variety of peppered moth, Biston betularia, to its darker variety (carbonaria) is due to mutation of a single Mendelian gene for survival in smoke-laden industrial environment.
(6) Phenomenon of "Industrial melanism" demonstrates natural selection.
(7) Biston betularia shows industrial melanism and it is the example of 'evolution taking place before the eyes'.