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Origin and Evolution of Life

Origin and Evolution of Life Synopsis

Synopsis

 

Evolution

  • Evolution can be defined as the formation of more complex organisms from pre-existing simpler organisms over a certain period. It is a slow, but progressive, natural, sequential development or transformation of animals and plants from ancestors of different forms and functions.     
  • Variation and heredity are the two basic factors of evolution. The selection of variants by the environmental factors forms the basis of evolutionary processes.



Speciation

  • All living organisms, including plants and animals, exist in the form of different species. 
  • A species is a group of organisms consisting of similar individuals which can breed together and produce fertile offspring.  
  • In plants, a vast diversity is observed with respect to the shape of leaves, colour of flowers etc. Despite this diversity, different plants, e.g. wheat, paddy, sunflower, lotus etc., are considered species of the Plant Kingdom. 
  • In human beings, although diversity is observed with respect to body features such as height and colour, all human beings belong to the same species Homo sapiens.
  • The process by which a new species develops from the existing species is known as speciation.
  • The biologist Orator F. Cook coined the term speciation.

Important Factors which Contribute to Speciation

 

  • Of these several factors, geographical isolation is the major factor in the speciation of sexually reproducing animals because it interrupts the flow of genes. However, it may not have any effect for self-pollinating or asexually reproducing plant species because they do not depend on other organisms for reproduction.

Evolution by Stages 

  • The number of plants and animals on planet Earth is enormous.  This great variety of organisms existing on the Earth initially was quite different from the one present now. They have modified themselves in response to their environment. These changes have occurred gradually in stages and have resulted in the evolution of a new species. The occurrence of different stages of evolution in a species is not because of a single DNA change.

Evolution of Eyes

  • The eye is an example of a complex homologous organ. It has been created in stages over generations. The primitive organisms which existed on the Earth were slow moving and smaller in size. They did not require a specialised organ for observing any object.




  • Consider the example of flatworms. Flatworms are small invertebrates. The eyes of flatworms are simple and exist in the form of eyespots. Eyespots are light-sensitive cells which can detect light. As evolution progressed, comparatively larger and mobile organisms evolved. Most of them were predators and required better vision for predation. Hence, from the basic design of eyes, more complex forms evolved. Insects, octopuses and invertebrates have eyes. However, the structure of the eyes differs in each of these organisms. This suggests that they have a separate evolutionary origin. The evolution of eyes is an example of evolution by stages.                                         

Evolution of Feathers

  • Birds make use of their feathers for flying. However, feathers did not evolve for flight. They evolved as a means of providing insulation to the body in cold weather.



  • Scientists have discovered fossils of dinosaurs which had feathers for insulation against cold weather. Because the dinosaurs were reptiles, it implies that birds evolved from reptiles.

Evolution by Artificial Selection

  • Artificial selection is the process in which human preferences have a significant effect on the evolution of a particular species. Example: Humans cultivate wild cabbage as a source of food and have produced different varieties of it by artificial selection. Common vegetables such as cabbage, kale, broccoli, cauliflower and kohlrabi are descendents of wild cabbage.