Origin and Evolution of Life: Organic Evolution and Theory of Organic Evolution (For CBSE, ICSE, IAS, NET, NRA 2022)

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Organic Evolution

The formation of complex organisms through gradual change from simple ancestral types over the course of geological time is known as Evolution or Organic evolution.

Theory of Organic Evolution

The various present-day organisms were not created in the same form in which they exist today but gradually evolved from many simple ancestral forms from a common ancestor. The characteristics of organisms had been changing in the past, today and in future also. This is happened because the environment in which organisms live is also changed and organisms need to adapt to the changed environment to survive. Several living organisms of the past have become extinct. The origin of the various forms (species) found on earth has been a gradual and extremely slow process and requiring hundreds or even thousands of years. The process of slow and gradual change is called Organic Evolution.

Evidences of Organic Evolution

The evidences supporting organic evolution are derived from a number of fields of Biology such as: Morphological evidences, Embryological evidences, Paleontological evidences and Molecular evidences

Evidences from Morphology

Yet organisms of different species and groups are quite different from each other but still have common features. The comparative study of various organs in different groups of vertebrates exhibit common features which show that they evolved from a common ancestor. Morphological evidences for evolution are derived from

Homologous and analogous organs

Have same structure and origin but different look and different function in homologous organs.

Homology and Adaptation in Bones of the Fore-Limbs …

In analogous organs, functionally similar but structurally different.

Analogy between Wings of Insects and Different Vert …

Vestigial organs

small degenerate or imperfectly developed organ/part which have been complete and functional in some ancestor.

Some Vestigial Organs in Human Body

Connecting links

Animals or plants have the characters of two different groups of organisms, e. g. Archaeopteryx a fossil bird which is a connecting link between reptiles and birds.

An Extinct Bird - Archeopteryx
  • Evidences from Embryology: Embryology is the study of development of an organism. In embryology all the different aspects support strongly the fact that vertebrates of different classes had common ancestors and by evolution process, differentiated from one to another.
  • Evidences from Paleontology: The study of fossils is called Paleontology. Fossils are the remains or traces of animal and plant life of the past, found embedded in rock either as petrified hard parts or as molds, casts or tracks. In earliest era the fossils are seen in bacteria, invertebrates and then fishes, amphibians, reptiles, birds and mammals and most recently primitive fossils of humans (mammals) are seen.
Series of Vertebrate Embryos in Comparable Stages O …
  • Molecular Evidence of Evolution: All organisms have the basic unit of life is cell and is made of biomolecules common to all organisms. Ribosomes are the cellular organelles of universal occurrence in organisms. DNA is the hereditary material of all organisms, except for some viruses. For biological process ATM molecule is stores and release energy. The central dogma of molecular biology explains the flow of genetic information in cells and protein synthesis basic steps transcription and translation in all organisms is the same.

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