Theories of Evolution for Competitive Exams

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Image of Theories of Evolution

Theories Of Evolution: (Lamarckism) By Jean Baptiste de Lamarck (Anthropology)

  • The problem of origin and evolution of man, strictly in its biological view point, needs the review of the origin of life in its broadest sense and of the different explanations.

  • Paleontology is one of the sciences which have made the greatest contribution to the knowledge of the genesis of life on earth and of its gradual evolution and complication.

  • Many theories were floated to explain the concept of evolution.

  • Let’s study some theories of evolution

LAMARCKISM

Image of LAMARCKISM

Image of LAMARCKISM

  • Lamarckism is the truly comprehensive theory of evolution. It was proposed by a French born biologist, Jean Baptiste de Lamarck (1744-1829). This theory is also called Inheritance of Acquired Characters and explains the origins of new species.

Image of Jean Baptiste de Lamarck

Image of Jean Baptiste De Lamarck

Jean Baptiste de Lamarck

  • In 1809, Lamarck put forth a complete thesis of evolution in his master work and classic book ‘Philosophie Zoologies’. The book included his theory explaining the changes.

Salient Features of Lamarckism

There are three salient features of Lamarckism

  • species change under changing external influence.

  • there is a fundamental unity underlying the diversity of species

  • the species progressively develops.

Lamarckism consists of four principles which are briefly discussed:

  • INTERNAL URGE: The internal forces of life tend to increase the size of an organism, not only as whole, but in every part as well up to the limit of their function.

  • DIRECT ENVIRONMENT AND NEW DESIRE: Each organ or part is the outcome of a new movement which in turn initiated by a new and continuous desire or want.

  • USE AND DISUSE: The development of an organ is in direct proportion to its use. Continued use strengthens the organ little by little until its full development is attained, while disuse has the opposite effect.

  • INHERITANCE OF ACQUIRED CHARACTERS: All that has been acquired or altered in the organization of individuals during their life is preserved and transmitted to new individual who proceed from those who have undergone these changes.

In support of his theory, Lamarck cited the following examples such as:

  • Development of strong biceps muscles in blacksmith.

  • Elongated body and loss of limbs in snakes due to continuous creeping through the holes and crevices.

  • Migration of both the eyes towards the upper side in fiat-fishes which are lying on the bottom of sea.

  • Lengthening of neck in giraffe due to its continuous use in reaching to leaves and fruits of high-rise trees.

  • Development of opposite digits, claws and muscular system to facilitate perching in birds.

Evidences and Experiments Against Lamarckism

  • Mutilation Experiment: Weismann was the main opponent of Lamarckian theory. He mutilated (cut) the tails of white rats and mated them but found no loss of tail in succeeding generation.

  • Artificial Parthenogenesis: Loeb produced artificial parthenogenesis in the Sea-Urchin eggs with the help of chemical stimuli. However, adults developing from such parthenogenesis need normal fertilization by sperm for development.

  • Boring of ears and nose: It is common practice in many societies. Many primitive societies mark their members with cuts on head, body and limbs. But such alteration in body is not transmitted to other generation.

  • Wearing of iron shoes by females in china: It is a practice to reduce size of their feet but their female child is born only with normal feet in the next generation.

Such practices and experiments prove that acquired characters are not inherited.

Criticism of Lamarckism

Lamarckism faced severe criticism and Lamarck had to defend them until his death. Some of the objections raised against the Lamarckism theory are as follow:

  • The first principle on the tendency to increase in size is true in case of many organisms. However, this is not universally accepted and there are instances to show reduction in size of the organs also.

  • The second principle ‘new organs develop upon new desires’ is also not true. If every human being who desires who desires to fly in the air s strong should develop wings, but such is not the case.

  • The third principle of Lamarckism, the use and disuse theory, has met with strong objections. If this theory is correct then the size of the eyes of person should also increase with age

  • The fourth and final principle ‘the inheritance of acquired characters’ has met with much contradictions.

Conclusion

  • In conclusion, rise and growth of Darwinism and Mentalism provided a scientific base for explaining process of evolution and Lamarckism was put in the background because it had no scientific base and its propositions were mostly make-believe.

  • On the other hand, mutation, recombination, hybridization, polyploidy, structural changes which produce variations are all scientifically testable.

  • Natural Selection, Isolation, Gene-flow, Genetic drift that shape variations into adaptive types and effect evolution are all corroborated by evidences and experiments.

#THEORIES OF EVOLUTION (LAMARCKISM)

#Lamarckism

#Jean Baptiste De Lamarckism

#Salient features of Lamarckism

#Principles of Lamarckism

#Evidences and Experiments against Lamarckism

#Criticism of Lamarckism

#Conclusion

#Physical Anthropology

#NET

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