In 1809, the French biologist Lamarck published the first modern theory of evolution in his book ‘Philosophie Zoologique’. Lamarck’s evolution theory states that all the traits that an organism acquires by responding to changes in the environment are passed on from one generation to the next. According to Lamarck, although two plants of the same species grow in two different environments, there are considerable differences between them.
Changes in the needs of organisms occur due to environmental changes. Organisms evolve among themselves to meet demand, that is, organisms adopt new methods. As organisms adopt new methods, the use of some organs is reduced and some organs are used in excess. In this way, new organs are developed from the organ that is used more. And unused organs become extinct. Lamarck’s theory is called Lamarckism. Lamarck’s theories are described below (1) & (3).
Lamarck’s theory or Lamarckism
Lamarck’s theories are based on a number of theories.
1. Influence of the environment
Lamarck believed that the change in the size of plants was due to changes in the environment. For example, the leaves in shadow zones (tropical zone) are large in size. When the same plant grows in the sun, the leaves become smaller. On the other hand, the root system of arid plants is more extensive than that of plants in humid regions. If the mesophyte plant is planted in a desert area and if it is able to survive in that environment for some reason, then the characteristics of the desert plant will gradually be revealed in that plant.
According to Lamarck, changes in the environment are directly responsible for changes in plants. But in the case of animals, the environment has an indirect effect. Environmental change causes changes in the structure or shape of the organism. According to Lamarck’s theory, the cause of the reaction between different animals or plants is a change in environmental conditions. From one generation to another, these effects of change accumulated from a new species (3).
2. Law of use and abuse of organs
Lamarck’s theory state that any part of the organism’s body that is constantly in use becomes stronger and well-organized. On the other hand, as a result of prolonged abuse, any organ becomes weak and inactive and eventually becomes extinct. Lamarck said that the use and abuse of the organ cause physical changes. Lamarck gave an example of organ use and abuse.
- Examples in favor of organ use
The neck of the giraffe’s ancestors was as small as a horse’s. But gradually the giraffe’s neck has lengthened in an attempt to collect the leaves of tall trees as food. As a result, their body shape has changed.
- Examples in favor of organ abuse
3. Law of inheritance of acquired characters
According to Lamarckism, the characteristics that an organism acquires under the influence of the environment and through its own efforts are passed on to the next generation of organisms. That is why Lamarck calls the inheritance of acquired traits. For example, the constant use of the neck lengthens the neck of giraffe ancestors. That is, the long neck is an acquired feature. This acquired trait is transmitted to his next generation of giraffes. So the next generation of giraffes also grows with long necks (3).
4. Conscious effort
Creatures are always trying to adapt to the ever-changing environment. It is an innate property of the organism. The organism undergoes various changes to adapt to the naturally changing environment. Lamarck states that organisms can change the course of evolution by continuously trying to grow or decay a particular organ. As the leaves of the small tree ran out, the giraffe continuously began to eat the leaves of the tall tree on its own effort. This conscious effort took place over a few generations. The giraffe’s neck gradually grows longer (3).
5. Origin of new species
New changes occur in the species due to the inheritance of acquired traits and the acquisition of new traits in each generation. And gradually new species are created. According to Lamarck, this is the primary region for evolution. For example, the giraffe’s neck gradually lengthens in each generation. As a result, the giraffe’s neck is much longer than that of its ancestor. And the shorter-necked giraffe gives rise to a new species (the long-necked giraffe) (1) & (3).
Examples in support of Lamarckism
Lamarck gave some examples in support of the theory in order to present his theory.
- According to Lamarck, giraffes originated from horses. The neck of the giraffe’s ancestors was like that of a horse. In the environment in which they lived, the number of leaves on the lower trees was less. So the neck and front legs have been gradually lengthened with each generation to eat the leaves of tall trees.
- Lamarck said in his theory that ostrich ancestors had active wings and could fly in the sky. But due to the environmental changes and the failure to use the wings for generations, the wings of ostrich have gradually become extinct. As a result, their physical constitution has also changed. And now ostriches can’t fly in the sky.
- Lamarck explains with the help of his theory that in the past the ancestors of snakes had four legs like lizards. Since snakes are capable of underground adaptation, they gradually stopped using their legs. As a result, the snake’s legs have gradually disappeared (3).
Criticism of Lamarckism
Lamarck’s theory of evolution is not above criticism. Various scientists have sharply criticized Lamarck’s theory. Two such scientists are Cuvier and Weismann. According to Cuvier and Weismann, Lamarck’s theory had no scientific basis. The critics of Lamarck’s theory are:
- According to Lamarck new organs are created according to the needs of the organism. This information of Lamarck is not scientifically acceptable. Because even if the environment has some influence, no new organ can be created by the inherent needs of the organism. If that were the case then man could create wings to meet his own needs.
- The formula on which Lamarck’s theory is based in the Law of inheritance of acquired characters. Scientists Weismann proved by some experiments that this information is scientifically baseless. Inheritance of acquired traits occurs only when they are transmitted by gametes. In this context, Wiseman has presented two experiments.
- In the first experiment, he cut the tails of a pair of male and female rats for 22 generations. And by breeding between them, he proved that no tailless rats are born.
- His second experiment was to keep drosophila flies in a dark room and breed them for 60 generations, there were no blind flies found. Weismann’s experiments prove that Lamarck’s theory is scientifically baseless.
- Mendel’s law of inheritance does not accept Lamarck’s theory.
- Lamarck’s law of use and abuse of organs is also not scientifically acceptable. This is because Lamarck provided some evidence in this source but did not prove it experimentally. Lamarck describes the tendency of organs to become smaller in the course of evolution. Lamarck did not describe the tendency of organs to grow.
Scientists such as Cope, Packard, Spencer, and Mac Bride slightly changed Lamarck’s theory based on the results of their various experiments and established a new theory called Neo-Lamarckism. In a word, the modern interpretation of Lamarck’s theory of ‘inheritance of acquired traits’ in the context of environmental organism interaction is called Neo-Lamarckism. According to the Neo-Lamarckism-
- The function of an organism and its relationship to the environment is the key to evolution.
- Differences or variations arise in the organism to adapt to the ever-changing environment
- Variants are transmitted through heredity and new species are created.
- Organisms are affected by the environment and the environment changes heredity.
- Of all the changes a person has made, some changes can be passed on to the offspring.
- Evolution is not affected by internal vitality.