EVIDENCES OF EVOLUTION
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Evidences for
evolution come from different lines of biological studies. These are palaeontology,
biogeography, morphology and comparative anatomy, embryology and genetics.
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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.
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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.
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Divergent evolution or adaptive radiation is the development of different functional structures from
a common ancestral form. It is based on homologous organs.
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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.
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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.
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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.
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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.
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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.
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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.
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Evidences from connecting link a connecting link demonstrates the characteristics of more
than one groups. These are as follows
|
Viruses |
Living and Non-living |
|
Euglena |
Animal and Plant |
|
Proterospongia |
Protozoa and Porifera |
|
Peripatus |
Annelida and Arthropoda
|
|
Neopilina |
Annelida and Mollusca |
|
Balanoglossus |
Chordates and Non-chordates |
|
Chimaera |
Bony fishes and Cartilaginous
fishes |
|
Lung fishes |
Fishes and Amphibians |
|
Archaeopteryx (also called missing link) |
Reptiles and Birds |
|
Duck-billed platypus |
Reptiles and Mammals |
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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.
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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.
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Geological time
scale represents the complete lifespan of earth, i.e. 4600 million years
arranged into ears, periods and epochs on a time scale
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Evidences from biogeography the study of patterns of distribution of animals and plants
on earth provides evidences of evolution.
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Evidences from taxonomy during taxonomic classification, organisms are grouped
according to their resemblance and placed from simpler organisms towards the
complex.
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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.
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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.