Classroom lecture on LamarckismTopic: Lamarckism
Today we are going to understand the theory of Lamarck about the origin of species. As you have learnt about organic evolution in which new and complex organisms are formed from simple organisms in a long period of time by the sequential and gradual change. We have already studied the proof of organic evolution. In today's lecture, we will study Lamarck's theory.
Lamarck made the first attempt to explain the origin of species in his theory which is known as the inheritance of acquired characters.
The theory of Lamarck can be explained in the following four steps:
1. All living organisms and their parts tend to increase continuously due to internal forces to meet their need.
2. Lamarck believed that environment plays a vital role in influencing the form of living organisms. The influence leads to change in their habits. The change in habits results in unusual activity of an organ or structure. Thus any change or changes in the organ or structures, forms or function of animal bodies are brought about in order to meet the needs, introduced by the changed or changing environment.
3. The efficiency, structure and development of an organ or organs are directly proportional to its use. It means the use of an organ enhances its efficiency and size leads to its better development. On the contrary, if any organ is not used by the possessor for a pretty long time it leads to the reduction in the efficiency and size of the organ and ultimately leads to its degeneration. The use and disuse of organs can be explained by taking an example of Giraffe. Lamarck presumed that the ancestors of giraffe had a short neck and both fore and hind limbs were equal in size. They used to live in grassy plains. When their ancestors were transferred to an area where there were only trees and no grass, they had to stretch their neck to reach the leaves of the trees high above the ground. Thus, more and more use of neck and forelegs resulted in the lengthening of these organs. The continuous stretching for several generations resulted in the appearance of long neck in the giraffe.
4. All those changes which have been acquired by the organisms during its lifetime due to the direct or indirect influence of environment are preserved by the generation and transmitted to the offsprings. Even in offsprings these modifications become more and more pronounced if they are exposed to the similar stress of the environment as was faced by their parents. Such cumulative effects will ultimately result in the formation of new species. For example, aquatic birds like ducks have been evolved from terrestrial ancestors. Since they had to go to water in search of food, a web-like structure developed between the toes, so that they could live in water easily.
So, this was the theory of Lamarck about origin of species. Tomorrow we will learn some criticisms of Lamarckism and a new theory of evolution.
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