Lamarckism was proposed by Jean-Baptiste de Monet Lamarck in the year 1744-1829. This theory was based on the principle that all the physical changes occurring in an individual during its lifetime are inherited by its offspring. For eg., the development of an organ when used many times. This theory has been explained here.
Lamarck’s theory includes four main propositions:
Change Through Use And Disuse
The organs which are used frequently by the organism develop and the characteristics that are used seldom are lost in the succeeding generations. For eg., a giraffe stretches its neck to eat leaves, a “nervous fluid” would flow in its neck and it enlarges. The organs which the organisms have stopped using would shrink with time.
Organisms Driven To Greater Complexity
As the organisms adapted to their surroundings, they became increasingly complex from the simpler forms. Lamarck believed in the spontaneous generation of life.
Also read: Evolution
Inheritance of Acquired Characters
An individual acquires certain characteristics during its lifetime. These characters are inherited by their offspring as well. He explained this with an example of a blacksmith. A blacksmith has strong arms due to the nature of their work. He proposed that any children a blacksmith conceives will inherit the development of strong muscles.
Effect of Environment and New Needs
The environment influences all the organisms. A slight change in the environment brings about changes in the organisms. This gives rise to new needs which in turn produces new structures and changes the habits of the organisms.
Examples of Lamarckism
Few of the examples of Lamarckism are mentioned below:
Evolution of giraffe
The ancestors of the giraffe looked like horses with small necks and forelimbs. They lived in areas where there was no surface vegetation. Therefore, they had to stretch their neck and forelimbs to eat leaves from tall plants. Consequently, these parts got elongated. This trait was transmitted in the successive generations.
Aquatic Birds with Webbed Toes
Aquatic birds such as ducks are believed to have evolved from terrestrial animals.
Extinction of Limbs in Snakes
The snakes are believed to have evolved from lizard-like ancestors that have two pairs of limbs.
It is believed that the ancestors of birds such as Ostrich were able to fly. Due to some environmental changes, they had a lot of food and were well protected. They stopped using their wings and as a result, the wings became vestigial.
The ancestors of the animals living in caves are believed to have powerful eyesight. Due to living under continuous dark conditions, they lost their power to see.
Lamarckism v/s Darwinism
Lamarck proposed theories like the inheritance of acquired characters, use and disuse, increase in complexity, etc. whereas Darwin proposed theories like inheritance, different survival, species variation, and extinction.
Darwin did not completely believe in his theory of acquired characters and proposed that the complexity in the organisms arise by the adaptation to the environment for several generations. Whereas Lamarck proposed that complexity arises due to usage or disuse of particular characters.
As the environment of an organism changes, so does his basic needs. The behaviour of the individual changes that eventually change organ usage and organism development. This gradual change in the species in response to the environment is known as “transmutation of species”.
Lamarckism was reformed by Giard and Cope by incorporating a few points of the opponents. This theory is known as Neo-Lamarckism.
Further reading: Natural Selection and Biological Evolution
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