Lamarckism: Theory, Propositions & Examples

Lamarckism is a biological theory of evolution encompassing a broad spectrum of theoretical approaches to the nature of evolution. Lamarckism is concerned with the genesis of biological forms, as well as their history and alterations. It was proposed by Jean-Baptiste de Monet Lamarck in the year 1744 -1829. According to the theory of Lamarckism, all the physical changes occurring in an individual during its lifetime were to be inherited by its offspring. The theory was criticized by most geneticists in the 1930s, but some of its concepts endured in the Soviet Union until the mid-twentieth century.

Key Terms: Lamarckism, Theory of Evolution, Inheritance of Acquired Characters, Somatic Alterations, Evolution, Offsprings, Genetics, Organisms, Genesis

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Lamarckism

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The theory is based on the principle that physical changes in organisms during their lifetime are inherited by their offspring. For instance, greater development of an organ or a part through increased use could be transmitted to their offspring.

Read More: Darwin's Contributions - Theory of Evolution

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Propositions of Lamarck’s Theory

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Lamarck’s theory involves four main propositions:

1. Change through Use and Disuse​

The organs that are utilized frequently by the organism develop in the subsequent generations, while the traits that are used infrequently are lost.

For example, the giraffe's progenitors were born with short necks and forelimbs so they could consume the leaves. When a giraffe bends its neck to consume leaves, a "nervous fluid" flows into its neck, causing it to grow. And over time, the organs that the organisms have stopped using would shrink.

2. Organisms Driven to Greater Complexity

Organisms tend to become increasingly complex as they adapt to their surroundings from simpler forms. Lamarck was an ardent believer in life's spontaneous generation.

3. Inheritance of Acquired Characters

An individual develops particular characteristics over time as a result of the use or disuse of a part or even as a reaction to an external alteration in the environment. These traits are passed down to their descendants.

The example of a blacksmith was used by him to illustrate his point. The nature of the work of a Blacksmith necessitates strong arms. He proposed that any children born to a blacksmith will inherit the ability to develop strong muscles.

4. Effect of Environment and New Needs​

All organisms are influenced by their environments. Minor changes in the environment result in changes in the organisms. This generates new needs, which in turn paves way for new structures and affect the organisms' behaviours.

Basic Idea of Lamarckism

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Examples of Lamarckism

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The following are some of the examples put forth by Lamarck to support his theories:

• Evolution of Giraffe: The giraffe's predecessors had tiny necks and forelimbs, similar to those of horses. Giraffes lived in those regions where there was no vegetation on the surface. Therefore, they had to elongate their necks and forelimbs to eat leaves from tall plants. As a result, certain parts grew longer. And therefore, this feature was passed down through the generations.
• Aquatic animals with webbed toes: Ducks and other aquatic birds with webbed toes are believed to have arisen from terrestrial species.
• Extinction of Limbs in Snakes: Snakes are assumed to have descended from lizard-like forefathers with two pairs of limbs.
• Flightless Birds: It is thought that the progenitors of birds like the ostrich could fly. They had enough food and were well sheltered due to various environmental modifications. They ceased to utilize their wings, and the wings became vestigial as a result.
• Dwellers in Caves: The progenitors of cave animals are thought to have had excellent eyesight. They lost their ability to see as a result of living in constant darkness.
• Flat-fish: Flat Fish- Deep-sea fishes live at the ocean's bottom, where there is no sunlight. As a result, they were forced to live a sedentary existence. The eye of one side, which is at the bottom, migrates up to the upper side. As a result, both eyes are focused on a single side of the body.
• Whales: Whales lost their hind limbs as a result of the hereditary consequence of disuse.

Example of Lamarckism

Read More: Acquired and Inherited Traits

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Criticism of Lamarckism

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Lamarck’s theory was subject to severe criticism. Cuvier and Weismann were the two scientists who were great critics of Lamarck. The following are some of the counter-arguments to Lamarckism:

• Although there is a propensity for individuals to become larger, they also shrink many a time. Trees that are primordial, for example, are enormous, whereas shrubs, herbs, and grasses that emerged later are tiny.
• A man should have evolved wings by now if new organs were to develop in response to a new need.
•  An organism's descendants cannot inherit changes accumulated during its lifetime. For example, if a person loses an arm in warfare, he does not have children who are born without one. Somatic alterations gained during an organism's existence are non-heritable, according to August Weismann, whereas changes in the germplasm or reproductive cells are passed down to the children.
• The theory of germplasm continuity is known as the Weisman theory. In 1904, August Weismann removed the tails of mice for 22 generations. The kids of the 22nd generation had the same length of tail as their parents.
• Mendel's law of inheritance refuted Lamarck's idea as well.

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Things to Remember

• The theory of Lamarckism states that the physical changes in organisms during their lifetime, such as greater development of an organ through increased use could be transmitted to their offspring. 
• It is referred to as the inheritance of acquired characteristics or more recently soft inheritance.
•  This theory was proposed by Jean-Baptiste de Monet Lamarck in the year 1744-1829.
• The theory involves four main propositions- Change through use and disuse, Organisms are driven to greater complexity, Inheritance of acquired characters, and Effect of environment and new needs.
• Lamarck’s theory was subjected to severe criticism by most geneticists.