Lamarckism: The theory of inheritance of acquired characters

Lamarck proposed his theory inheritance of acquired characters to explain the origin of new species through the process of evolution. This article deals with the main assumption of Lamarck's with example and the criticisms of Lamarckism and Neo-Lamarcksim.

Introduction

The study of different kinds of pieces of evidence of organic evolution confirms that evolution has definitely taken place in the organism. To explain the evolution in the organism, Lamarck proposed the theory of inheritance of acquired character which is known as Lamarckism. He wrote the book "Philosophic Zoologique" in which he elaborated on his doctrine of evolution. Lamarck is the first scientist who has made the first attempt to explain the origin of species and their adaptation to the environment. He was the first naturalist to conclude that evolution is a general fact covering all forms of life. Lamarckism states that changes which the organism acquires in adaptation to the environments which it meets during its whole life are automatically transferred to its descendants and so become part of the inheritance.

Assumptions of Lamarckism

The theory of inheritance of acquired characters is comprised of the following four assumptions:

Origin of needs due to t internal vital forces

Direct environmental effect over living organisms

Use and disuse of organs

Inheritance of acquired characters

Origin of needs due to internal vital forces : The internal forces of the body tend to increase continuously the size of organisms and their component parts.

Direct environmental effect over living organisms: Environment play a vital role in influencing the form of the living organism. The influence leads to a change in their habits or behaviour of the organism. These changes in habits or behaviour result in the unusual activity of an organ or structure. Thus, any change or changes in the organs or structures, form or function of the animal body are brought about in order to meet the needs, introduced by the changes or changed environment.

Use and disuse of organs: The constant use of organs enhances its efficiency and size leads to its better development. The Organs which are more extensively used would enlarge and become well developed. Conversely, an organ or organs, no longer used, would be degenerate and atrophy. The doctrine of desires is called appetency.

Inheritance of acquired characters: The changes brought about by use and disuse of organs and by the influence of environmental factors in an individual during its lifetime are called acquired characters. All those changes which are acquired by the organism during its lifetime due to direct or indirect influence of the environment are preserved by the generation and are transmitted to the next generation. Even in offspring these modifications become more and more pronounced if they are exposed to similar stress of the environment as was faced by their parents. Such cumulative effects will ultimately result in the formation of new species.

Examples of Lamarckism

The following examples are given in favour of Lamarckism:

Evolution of long-necked Giraffe

Giraffe is a mammal with a very long neck and long forelimbs. Lamarck presumed that the ancestors of giraffe lived in Africa were deer-like with a short neck and both fore and hind limbs were equal in size. They lived in places where the ground was almost invariably parched and without trees. When these ancestors were transferred to an area where there were only trees and no grass, they were continuously stretch their necks to reach the leaves of trees, high above the ground. The 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 a long neck in giraffe.

Snakes

Present-day snakes with the long slender body are evolved from a limbed lizard-like ancestors. Due to continuous disuse of limbs and stretching of their body to suit their creeping mode of locomotion and to accommodate their body in narrow space out of fear of larger and more powerful animals, the present-day snakes have been evolved.

Aquatic Birds

Ducks and other aquatic birds have been evolved from terrestrial ancestors. Since they had invaded water from land in search of enough food because enough food was scared on land and these birds did not have the power to fly. The duck would stretch its toes apart to provide more push during swimming in water. This led to the development of webbed toes so that they could live in water easily.

Criticism of Lamarckism

The greatest drawback in Lamarck's work was that it was too theoretical and there was no proof to support it. His ideas were based on theory but practically they had no standing. He met severe criticism from various scientists:

The most serious criticism came from Weisman who put his theory of continuity of germplasm, According to his theory, heredity is the sole concern of germ cells. Characters introduced in the germ cells will only be transmitted and not those which are present in somatic cells.

If the acquired characters were to be inherited, as Lamarck said, the world would have been full of cripples, blinds and deformed persons, as most of these characters are acquired.

Some workers have practically proved that mutations are not inherited by offsprings even if practised for a generation.

Neo-Lamarckism

Many evolutionists were found to be supports the theory of inheritance of acquired characters. These come under the heading of Neo-Lamarckism. These evolutionists are Cope, Giard, Spencer, Mc. Bride, T.H. Morgan, etc. Neo-Lamarckism states that:

Adaptation is universal. It arises due to the causal relationship of structure, function and environment.

Germ cells are also affected by environmental changes.

Environment influences the organism and change its heredity.

The variations acquired by an individual can be transmitted to the next generation.

Germ cells may carry acquired characters or somatic variations to the offsprings.

Internal vital forces do not have any role in evolution.

Conclusion

The main error in Lamarckian thought and Neo-Lamarckism is that both assumed the inheritance of acquired characters. In Lamarckism, the acquired characters result from needs while according to Neo-Lamarckism these will be induced due to environment and habit. Use and disuse of Lamarck's thought were retained in Neo-Lamarckism.

Lamarckism and Neo-Lamarckism were not accepted by the scientists and after some years Darwin proposed the theory ofnatural selection to explain organic evolution.

Lamarckism: The theory of inheritance of acquired characters

Introduction

Assumptions of Lamarckism

Examples of Lamarckism

Evolution of long-necked Giraffe

Snakes

Aquatic Birds

Criticism of Lamarckism

Neo-Lamarckism

Conclusion

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