Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck, popularly known as Lamark was a french naturalist who proposed the first theory of evolution in 1801 even before Darwin’s theory of natural selection was introduced (1859). Lamarck’s theory is commonly known by names such as Lamarck’s theory of evolution, use or disuse theory, the theory of acquired characteristics, Lamarckism, Lamarckian evolution etc. His theory was mainly based on the interaction of an organism with its environment, the frequency of use or disuse of an organ and inheritance of the acquired characteristics into the next generations. He believed that evolution is a preplanned process and the results have been concluded already. Now let us try to understand Lamarck’s theory and his beliefs step by step.
Main points of Lamarck’s theory
- Lamarck believed that an organism adapts itself with the environment. These adaptations are transferred to the next generation up to the point when no further adaptations (improvements) are needed.
- He said that the environment plays a crucial role in forming the shape and structure of an organism.
- Therefore according to Lamarck, interaction with the environment and use and disuse of an organ plays a crucial role in evolution.
- He believed that if an organism is bringing any change in its characteristics during its lifetime to adapt to the environment, these changes will be transferred to the next generation.
- Lamarck said that these characteristics that are being adopted by organisms with environmental interactions and use and disuse of organs and are then being inherited into the next generation are known as acquired characteristics.
- Acquired characters are those changes that are acquired in the body of an organism during their lifecycle in the somatic cells, mainly in order to adapt to the environment. He believed that these changes (acquired characters) if displayed by one or more organisms of a population, will be displayed/transferred in the next generation of the organisms.
- Lamarck said that these acquired characters are developed by the use and disuse of the organs. That is the organs that are used frequently by an organism become the acquired characters (hence transferred to the next generation) and those organs that are not used become vestigial and are ultimately vanished from subsequent generations. Therefore this theory is also known as the theory of use and disuse.
Laws of Lamarckism
There were two laws proposed by Lamarck in his theory that simplified what is explained in the above points. These two laws are:
First Law: Use and Disuse of Organs
In this law, Lamarck simply explained that those organs that are frequently and continuously used will be transferred to the next generation. These organs will become stronger, develop rapidly and enlarge in each generation. In contrast to this, those organs that are less used will slowly lose their functionality and will ultimately vanish from future generations. For example, the vestigial organs and human tail can be the example given to support this law.
Second Law: Inheritance of Acquired Characters
The characters which are developed by the environmental interaction and use and disuse of organs will ultimately lead to the formation of certain characters called as acquired characters and these characters must be inherited to the young ones for the evolution to take place. The acquired characters are only transferred to the next generation if both the mating partners have the same set of acquired characters or at least the one producing the offspring. This law by darwin
Examples Supporting Lamarck’s Theory
- Giraffe Neck
One classical example used to explain the Theory of Lamarckism is the neck of Giraffe. According to Lamarck, Giraffe had a short neck initially but when the resources became limited to the tall trees, in order to reach for the tall branches, Giraffe grew longer necks gradually in the next generations.
- Elephant Trunk
Initially, the trunks of the elephants were short but when the resources started vanishing from the ground and were limited to the tall trees, with the frequent and continuous use, they grew longer trunks in their future generations.
- Webbed toes of Aquatic birds
The aquatic birds are evolved from the terrestrial ancestors and therefore developed webbed toes in order to swim underwater.
- Limbs in snake
Snakes are believed to have evolved from lizards and had two pair of limbs. But during the course of evolution, those limbs got disappeared therefore pointing towards the theory inheritance of acquired characters.
- Flightless Birds
Flightless birds like Ostrich, have evolved from birds that were able to fly. But due to abundance of the resources on the ground, these birds lost their ability to fly and ultimately loss of function occurred in their wings.
Evidence opposing Lamarck’s Theory
Lamarck’s theory of use and disuse of organs and inheritance of acquired characters is the most criticised evolutionary theory. Many biologists later proved this theory wrong by giving counter theories and examples in real life. Darwin’s theory of natural selection was the most accepted theory and later on Darwin’s theory was improved by connecting it with Mendelian principles and it was given the name, Neo-Darwinism. Neo-Darwinism is currently the most accepted theory of evolution.
The biggest criticisers of Lamark’s theory were Mendel and August Weismann. Mendel’s law of inheritance discarded Lamarck’s theory of inheritance of acquired characters, while August Weismann’s theory of Germplasm discarded Lamarkism concept.
- Theory of Germ Plasm
The theory of Germ Plasm was given by a German Biologist, August Weismann in 1894. This theory is also known as continuity of germplasm because according to Weismann the characters are transferred to the next generation by the germ cells. He discarded Lamarck’s theory as he said that only those changes that will happen in the germ cells will be inherited into the next generation while the changes in the somatic cells will not be transferred.
To understand this more clearly, let us quickly try to understand the concept of Germ cells and Somatic cells.
These are the cells of the gametes containing chromosomes that fuse with the similar kind of cells of the opposite gender and form a zygote which leads to the development of a whole organism. Therefore these cells are also known as sex cells and any change in the DNA of germ cells will be carried forward to the offspring (Continuity of Germplasm).
These are the cells of the whole body other than the germ cells. These cells do not take part in fertilization but in the development of the body of an organism. Therefore any change in the DNA of somatic cells won’t cause any change in the offspring. Another major difference between somatic and germ cells is that while dividing, somatic cells will only undergo mitosis while germ cells undergo both mitosis and meiosis.
To prove the theory of Germplasm, Weismann experimented on rats. He cut off tails of rats for 22 generations but after every generation, no rat was born tailless hence completely discarding the Lamarck’s theory of inheritance of acquired characters.
Other common examples that oppose Lamarck’s theory are:
- Boring of the ear pinna
The ear pinna is bored by many Indian women, but their daughters are born with normal ears.
- Small feet of Chinese women
Chinese women used to wear tight iron shoes to compress their feet size in order to look attractive. But this character was never inherited in their offsprings.
- Wearing rings around the neck
The women of Kayan Lahwi tribe (Mayanmar) wear brass coils around their neck in order to look attractive and exhibit sexual dimorphism. This compresses their shoulders downwards giving an illusion of long necks. This character of longer necks is also never inherited into their daughters.
- European Corset
European women used to wear tight corset tops in order to have their waist thin but their daughters were born with normal waists.
- Human eye
Considering the theory of use and disuse of organs, the human eye is an example that disproves this theory. Humans use their eyes the most but with age it gets dysfunctional. Also, the offsprings are never born with extra strong eyesight but with a normal vision.