Introduction to Lamarck's Theory of Evolution
Lamarckism has covered a broad spectrum of theoretical positions on the nature of evolution. Jean Baptiste Lamarck presented theories on Lamarckism. There were numerous explanations given from the 18th century until the early 20th century. Lamarckism is about the succession of life forms, their history, their transformations. Darwin believed that individuals were simply born with different traits and these differences were mostly random. This theory was contrary to Lamarck who said that traits could develop change during an animal's life. The theory is. based on evolution stated that physical changes in organisms during their life-likee, in a part through increased use or greater development of organs could be transmitted to their offspring.
Inheritance of Acquired Characteristics
Characteristics that have been developed by an individual in the course of their life in the body or somatic cells are usually through the use or disuse of part or an immediate reaction to some external modification in the environment. The reappearance of variations from an individual in the next or succeeding generations is known as the inheritance of acquired characteristics. Inheritance of a change can be explained through an example of Blacksmith's arm.
When the arm is used continuously against an external resistance like the weight of the hammer then blacksmith's arm enlarges. At the birth, the smith’s children would have unusually large arms, if the effect were inherited.
Theory of Use and Disuse
Lamarck tried to explain the evolutionary process in his book Philosophic Zoologique. The use and disuse of an organ lead to acquiring changes in the feature of the organ. These changes are also inherited to offspring. ButLamarckismm was very strongly criticized by August Weismann.
Lamark's Theory of Inheritance of Acquired Characteristics
The first theory of evolution is Lamarckism which was proposed by a French biologist. It states that modifications acquired by an organism during its lifetime are automatically handed down to its descendants, and so it becomes part of heredity. His evolution ideas are briefed as follows:
1. The Size of the Organism Tends to Increase with Internal Forces
The internal forces of life tend to increase continuously the size of an organism and its components.
2. The Direct Environmental Effect Over Living Organisms
The organs of an animal show modifications in a way that they respond directly to a changing environment.
3.Use of Disuse
More use of organs greatly improves them and misuse reduces the organs.
4. Inheritance of Acquired Characteristics:
It is the direct transmission of those superficial bodily changes that arose within the lifetime of an individual.
Examples of Lamarckism
Lamarckism explained his theory by giving the following examples
Giraffe- The giraffe’s ancestors were born a small neck and forelimbs to eat the leaves for food, which resulted in the slight elongation of these parts. The acquired characters were transmitted to the next generation.
Aquatic Birds – Evolution of Ducks occurred from terrestrial ancestors. Due to the lack of food on land, these aquatic animals need to go to water. Hence, some web-like structures are developed between the toes in them making their lives easy in the water.
Flat Fish- Deep-sea fishes are found at the sea bottom where no sunlight is present. So, they had to lead an inactive life. The eye of one side which lies on the bottom then migrates towards the upper side. Thus, both eyes are on the single side of the body.
Whales- as an outcome of the inherited effect of disuse, lost their hind limbs.
The Wadding Birds- like Jacana keep their body above the water level by developing long legs through the sustained stretching generation.
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Drawbacks in Lamarckism
Lamarckism is not proved experimentally.
New organs are not formed in organisms as per their wish.
It is not necessary that the acquired characters transmit into the new generation.
1.Compare Lamarck and Darwin Theories of Evolution
Difference between Lamarckism and Darwinism is as follows:
The theory of Lamarck was proposed by Jean Baptiste Lamarck.
The population of individuals has identical characteristics. Individuals are capable of transformation.
Internal run towards the complexity which is greatly modified by the inheritance of acquired characteristics. the direction of variation is towards the organism’s needs.
Giraffe with a long neck is an example of Lamarckism.
Darwinism was proposed by Charles Darwin.
Interbreeding individual populations have had identical characteristics with specific variations at all times. People are unchanging. The population is capable of transformation.
Regardless of the organism's requirements, variations occur. It is not directed toward any purpose.
Hawk with keen eyesight is an example of Darwinism.
2.Explain Darwin’s Theory of Natural Selection
Charles Darwin the Naturalist stated in his theory of natural selection that all species of organisms arise and develop small inherited variations that increase the individual’s ability to compete, survive, and reproduce. The theory has two main points, in which he has explained that all life forms on Earth are related to each other. The diversity in life forms is the result of modifications in populations and due to the process of natural selection. Due to natural selection, some traits could be favored in an environment and others couldn’t be favored. The theory is well known as “ Survival of the fittest ones”. It can be misleading so popular referred fitness not to an organism's strength or athletic ability but the ability to survive and reproduce.