Theory of Evolution: Lamarckism

^{Theory of inheritance of acquired characters or Lamarck’s theory of evolution}

^{The theory of evolution given by French   biologist Jean Baptist de Lamarck (1744 – 1829) is called as Lamarckism.}

Lamarck

^{Introduction to Lamarck}    

           

^{—    Jean Baptist de Lamarck was a French naturalist born in 01 August 1744 AD in Bazentin, France and died in 18 December 1829 in Paris, France. He was soldier, biologist and academician.}

^{—    He was first biologist to give the formal theory of evolution.}

^{—    In 1809 AD, He published a book entitled    “ Philosophique zoologique”, Zoological philosophy in English and explained his view on evolution.}

^{Postulates of Lamarckism}

^{This theory can be explained under following headings}

^{—    Effect of environment}

^{—    Use and disuse of organs}

^{—    Inheritance of acquired characters}

^{—    Speciation}

^{Effect of environment}

^{Living organisms are found in some kind of environment which has direct influence on the survival of the organisms. The change in environmental factors results into new needs in living organisms. To fulfil  these new needs organisms have to exert special efforts like change in habitat, habit, behavior etc.}

^{Use and disuse of organs}

^{The new needs involve greater use of some organs while less or no use of some organs. This is called as use and disuse of organs. This directly affects form, structure and functioning of the concerned organs. The continuous and extra use of organs make them more efficient , stronger and larger while continuous disuse of organs make them degenerate and disappear.}

^{Inheritance of acquired characters}

^{Due to use and disuse of organs new characters get developed in organisms and are called as acquired characters. These acquired characters get inherited from parents to their offspring.}

^Speciation

^{As the acquired characters get inherited for many generations new organisms are formed and this process is called as speciation.}

^Examples

^{1.Giraffe:    Long neck and long forelimbs of present day Giraffe from Deer like ancestors is due to continuous use and elongation of them for long period of time. The Deer like ancestors started to stretch their forelimbs and neck to obtain food from the branches of trees as there was scarcity of foods on ground. The  over use of neck and forelimbs resulted in the elongation of them and the stretched  neck and forelimbs get inherited to offspring continuously for many generations and resulted in the formation of present day form.}

^{2. Snakes:- Development of present day limbless and slender body of present day snakes from limbed and short body is due to continuous no use of limbs and stretching of body while creeping through thick vegetation and in the gaps of stones.}

^{3.Aquatic birds:-  Development of webbed hindlimbs is due to continuous swimming and reduced wings is due to less use of wings.}

^{4.Moles:-   Reduction of eyes in moles is due to less use of eyes as they lived in underground.}

^{5. Horse:-   The ancestors of horse had 4 digits and 3 functional toes. As they started to live in hard and dry area there was no use of digits for fast running. Thus, the number of digits was reduced.}

^{Limitations/ Criticism}

^{1.German biologist “August Weishman” performed an experiment in which he cut the tail of mice for 20 successive generations but the mice of 21st generations were also with tail.  on the basis of this experiment he formulated “ Germplasm theory” In 1892. This theory states that two types of cells; somatic cells and germ cells are found in organisms. The environmental factors can bring change only in somatic cells and the change in somatic cells cannot get inherited. Only the changes in germ cells get inherited.}

^{2.Piercing of pinna and nose among Hindu women has been practiced for centuries but their children never born with bored pinna and nose.}

^{3.Powerful muscles in the body of wrestlers do not get inherited to their children.}

             ^{Think further}

^{—    .Though this theory is not accepted nowadays, it is of great importance as it is first formal theory to explain the process of evolution.}

^{—    * It is based on “inheritance of acquired characters” which is the gist of this theory.}

^{—    *The characters developed during life time i.e. after births are called acquired characters.}

^{—  *  The transfer of characters from one generation to another generation is called inheritance.}

^{—   * The idea of changing species was quite different then existing belief of fixity of species.}