Evolution - Theories Of Evolution-Mutation Theory| NCERT concept | Neet Concept | Biology

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THEORIES OF EVOLUTION

• Various theories have been put forward to understand and explain the process of evolution by many scientists such as Lamarck , Darwin , de Vries , etc.
• The first theory of evolution was proposed by Jean Baptiste de Lamarck in 1809 and was published in ' Philosophie Zoologique ' . It is popularly known as Lamarckism .
• According to Lamarckism :
• Doctrine of desire- Changing environment gives rise to new needs in an individual .
• Use and disuse of organs - Continuous use of an organ leads to its development and disuse results in degeneration .
• Inheritance of acquired characters means structural and functional changes acquired during lifetime of an individual are inherited by its offspring and by accumulation of acquired characters new species originates . E.g. , disappearance of limbs in snakes , evolution of flightless birds from their flying ancestors , etc.
• Theory of continuity of germplasm- Experiments conducted by A. Weismann discarded the law of inheritance of acquired characters . It proved that only those characters affecting germ cells are inherited . It proved the continuity of germplasm and not the somatoplasm to the next generation .
• According to Neo - Lamarckism , a modified form of Lamarckism , the acquired characters which become incorporated in the germplasm are heritable and accumulation through generation after generation results in the origin of new species .
• The ' Theory of Natural Selection ' was put forward by Charles Darwin in 1858 .
• The main features of the theory of natural selection are :
• Over production : All organisms possess enormous fertility and multiply in geometric ratio .
• Limited food and space : Food and space remain almost constant , so , they affect survival of an individual .
• Struggle for existence : Limited supply of food and space causes struggle for existence either between individuals of same species or different species .
• Appearance of variations : Continuous struggle for existence compels organisms to change according to conditions in order to survive successfully . This produces variations among individuals .
• Natural selection : Organisms with favourable variations survive and are better adjusted to the changing environment . Originally it was an idea of Herbert Spencer who termed it as ' Survival of the Fittest '  Darwin named it as Natural Selection . Organisms capable of adapting to the changing environmental conditions have better rate of survival .
• Inheritance of useful variations : Only useful variations acquired by organism are transmitted to next generation , while non - useful variations get eliminated .
• Formation of new species : Useful variations keep on accumulating and are transmitted to generation after generation and new species is formed .
• Mutation Theory was proposed by Hugo de Vries in 1901. According to this theory new species originates due to discontinuous variations or mutations which appear suddenly . Mutations are subjected to natural selection where mutants found unsuitable are destroyed .

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MANISH MEVADA

M.Sc, M.Phil, B.Ed

GUJARAT BIOLOGY NEET

NEET MATERIAL IN GUJARATI 

KNOWLEDGE ON THE WAY.