Theory of Evolution : Lamarckism and Darwinism

02/01/2021 Vinod 0 Comments

Theory of Evolution :-

Modern theory of evolution is based on Darwin’s work related to the natural selection. It is not a hypothesis, theory of evolution includes Lamarckism, Darwinism.

Lamarckism :-

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Fig. 1. Lamarck ( 1774 – 1829 )

Jean Baptiste de Lamarck ( French ) published a book named Phylosophic Zoologique in 1809. In which he explained the process of evolution by suitable examples. Therefore Lamarckism is also known as first comprehensive mechanistic theory of evolution.

Lamarckism is explained under three heads –

  1. Use and Disuse of Organs.
  2. Effects of environment.
  3. Inheritance of acquire characters.

1. Use and Disuse of Organs :-

Those organs which are used regularly, get more evolved, similarly the organs which are used rarely or not used at all, get degenerated and become vestigial or non-functional.

The presence of vestigial organs in the body can be explained only by Lamarckism.

2. Effects of environment :-

The development of morphological and anatomical features are effected by the environment.

3. Inheritance of acquired characters :-

The characters which acquired by an organism are inherited by the Offspring causing evolution.

Examples in support of Lamarckism :-

( a ) Long neck and fore limbs of giraffe.

lamarckism
Fig. 2. Evolution of giraffe

( b ) wading type legs in ducts.

( c ) Mac Dougall’s experiment in case of guinea pig.

( d ) Kammerer’s experiment in case of salamander.

Neo Lamarckism :-

The new lamarckism such as Spencer, Cope, Packard, Kammerer, Smith etc. were the supports of Lamarckism.

They opposed Darwinism.

Examples against Lamarckism :-

  1. Boring on nose and ear.
  2. Development muscles of black smith is not inheritance by the Offspring.
  3. Poulose experiment which proved that the learning cannot be inheritance.
  4. Weismann’s mutilation experiment which proved the mutilation of tail in guinea pig does not effect in growth and length in the Offspring.
  5. Castle & Phillips physiological experiment which proved that the implantation of ovaries of black guinea pig into the body of white female guinea pig does not resulted in the production of white Offspring.
  6. The Lamarckism was discarded as modern genetics proved that all the acquired characters which are present in the somatic cell, cannot be inheritance.

Darwinism or Darwin Theory of Evolution :-

Darwinism as a philosophical concept started from the ideas of Charles Darwin concerning
Fig. 3. Charles Darwin ( 1809 – 1882 )

Darwinism is the theory of evolution developed by the English Naturalist Charles Darwin. stating that all species of organisms arise and develop through the natural selection of small inherited variations that increase an individual’s ability to complete, survive and reproduce.

  • Natural selection :- Natural selection is the process in which living things with beneficial traits produce more Offspring than others do, this results in changes in the traits of living things over time.
  • It originally included the broad concepts of evolution which gained general scientific acceptance after Darwin published book The Origin of Species in 1859, including Concepts which predated Darwin’s Theory of Evolution.
  • Through his observations and studies of birds, plants and fossils Darwin noticed similarities among species all over the globe along with variations based on specific locations, leading him to believe that the species we know today had evolved from common ancestors.

There are the basic points of evolution by natural selection as defined by Darwin –

  1. more individuals are produced each generation than can survive.
  2. Phenotypic variation exists among individuals and the variation is heritable.
  3. Those individuals with heritable traits better suited to the environment will Survive.
  4. When productive isolation occurs new species will form.
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Fig. 4. Evolution through natural selection.

Neo Darwinism :-

Neo Darwinism is generally used to describe any integration of Darwin’s theory of evolution by natural selection with Gregor John Mendel‘s Theory of genetics. It has been variously modified since it was first proposed.

  • Theory of evolution represents a synthesis of Charles Darwin’s theory in terms of natural selection and modern population genetics. The term was first used after 1896 to describe the theory of Weismann ( 1834 – 1914 ), who asserted that his germ plasm Theory made impossible inheritance of acquired characters and supported natural selection.

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