Question
Describe the Lamarkism in relation to organic evolution.
✓
Answer
Lamarck was one of the most brilliant stars on the horizon of the history of evolution.
He was the first naturalist to put forward a general theory of evolution in his famous book Philosophic Zooligique published in 1809. His evolutionary theory may be summarised in the form of following laws :
(1) The internal forces of life tend to increase the size of an organism.
(2) The necessity in animals produces new structures.
(3) The effect of use and disuse of organs.
(4) Inheritance of acquired characters.
(1) The internal forces of life tend to increase the size of an organism : Lamarck believed that there is some kind of internal force which is constantly working in living beings. It tries to make the animal bigger in size.
(2) The necessity in animals produces new structures : According to this law, each organ and structure is the product of some continuous necessity in the animals to develop it. He believed that it was not due to the direct influence of the environment but acted through the nervous system, the process being very slow. The plants, he said, were directly influenced by their environmental conditions.
(3) Effect of use and disuse of organs : Lamarck thought that the continuous use of a particular organ or structure tends to increase its size and its development. On the other hand, disuse results in disappearance of that structure, the process being slow and gradual. He supported this by a number of well-known examples. The long neck giraffe was the result of continuous stretching to obtain food from the trees (long neck was acquired due to excessive use) The wings of certain birds Ratitae were not used for long, as there were no formidable enemies and food was available in abundance. So they did not fly, consequently lost the power of flight. Their wings became rudimentary (flightless condition acquired due to the disuse of wings.)
(4) Inheritance of acquired characters : Lamarck in 1815 stated that all the characters, which are acquired in one's own lifetime are inherited by its offsprings.
He was the first naturalist to put forward a general theory of evolution in his famous book Philosophic Zooligique published in 1809. His evolutionary theory may be summarised in the form of following laws :
(1) The internal forces of life tend to increase the size of an organism.
(2) The necessity in animals produces new structures.
(3) The effect of use and disuse of organs.
(4) Inheritance of acquired characters.
(1) The internal forces of life tend to increase the size of an organism : Lamarck believed that there is some kind of internal force which is constantly working in living beings. It tries to make the animal bigger in size.
(2) The necessity in animals produces new structures : According to this law, each organ and structure is the product of some continuous necessity in the animals to develop it. He believed that it was not due to the direct influence of the environment but acted through the nervous system, the process being very slow. The plants, he said, were directly influenced by their environmental conditions.
(3) Effect of use and disuse of organs : Lamarck thought that the continuous use of a particular organ or structure tends to increase its size and its development. On the other hand, disuse results in disappearance of that structure, the process being slow and gradual. He supported this by a number of well-known examples. The long neck giraffe was the result of continuous stretching to obtain food from the trees (long neck was acquired due to excessive use) The wings of certain birds Ratitae were not used for long, as there were no formidable enemies and food was available in abundance. So they did not fly, consequently lost the power of flight. Their wings became rudimentary (flightless condition acquired due to the disuse of wings.)
(4) Inheritance of acquired characters : Lamarck in 1815 stated that all the characters, which are acquired in one's own lifetime are inherited by its offsprings.
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