Important Notes Of Evolution For NEET


        Evidences for evolution come from different lines of biological studies. These are palaeontology, biogeography, morphology and comparative anatomy, embryology and genetics.

        Evidences from morphology and comparative anatomy it is seen that inspite of a large number of organisms unlike in appearance they show most of the systems and organs made on the same plan. This provides evidence of common ancestry.

        Homologous organs are those organs, which have same embryonic origin and basic structure, they may or may not perform the same function and this phenomenon is known as homology, e.g. forelimbs of vertebrates.

        Divergent evolution or adaptive radiation is the development of different functional structures from a common ancestral form. It is based on homologous organs.

        Analogous organs are the organs which are different in their basic structure and developmental origin, but appear similar and perform similar functions. This phenomenon is known as analogy, e.g. wings of insects and wings of birds.

        Adaptive convergence or convergent evolution is a phenomenon when separate lineages show similar morphology under the influence of similar environmental factors. It is based on analogous organs.

        Vestigial organs are rudimentary non-functional organs in the possessor, but were functional in their ancestors and in related animals, e.g. nictitating membrane, coccyx (tailbone), vermiform appendix, etc.

        Atavism or reversion is the sudden reappearance or refunctioning of some ancestral organs, which have either completely disappeared or present as vestigial organs, e.g. long and dense body hair power of moving pinna, etc.

        Evidences from embryology Von Baer is known as father of embryology. He put forward Baer’s law that revealed the fact about the sequence of development of structures in organisms. It says that more general features appeared first then came less general features and lastly came specialised features in an organism.

        Biogenetic law or recapitulation theory was postulated by Ernst Haeckel by combining the ideas of Darwin’s evolution and Baer’s law. It states that ontogeny recapitulates phylogeny.

        Evidences from connecting link a connecting link demonstrates the characteristics of more than one groups. These are as follows


Living and Non-living


Animal and Plant


Protozoa and Porifera


Annelida and Arthropoda


Annelida and Mollusca


Chordates and Non-chordates


Bony fishes and Cartilaginous fishes

Lung fishes

Fishes and Amphibians

Archaeopteryx (also called missing link)

Reptiles and Birds

Duck-billed platypus

Reptiles and Mammals


        Evidences from palaeontology the study of fossils and their interpretations from one of the great evidences of evolution. Fossils are the material remains (bones, teeth, shells) or traces (physical or chemical) of ancient organisms. These are found preserved in earth’s sedimentary rocks. The age of the fossils or rocks can be determined by radioactive carbon (C14) dating method, radioactive clock method or electron spin resonance method.

        Living fossils are the organisms that are similar in appearance to their fossilised distant ancestors and usually have no extinct close relatives, e.g. Neopilina, Nautilus, Tuatara, etc.

        Geological time scale represents the complete lifespan of earth, i.e. 4600 million years arranged into ears, periods and epochs on a time scale

        Evidences from biogeography the study of patterns of distribution of animals and plants on earth provides evidences of evolution.

        Evidences from taxonomy during taxonomic classification, organisms are grouped according to their resemblance and placed from simpler organisms towards the complex.

        This provides us an idea about which animal came first according to the evolutionary point of view. Also it tells us about resemblance between two different animals.

        Evidences from biochemistry and physiology biochemical and physiological analysis of organism suggest a common origin for living things. The biochemical differences between the living organisms make it possible to measure the relatedness of different groups of organisms by the amount of differences between specific molecules such as DNA, proteins and enzymes.

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