Process of evolution is the slow and gradual modification of organisms by which a primitive form of organism modified through descend and transformed into advanced so as to reached at the present day conditions. Mechanism of evolution can not be experimented within the short life span of a man. So there is no remarkable experimental evidence to explain the mechanism of evolution, it can be studies on the basis of observed facts and theoretical concepts.
Lamarckism refers to the theoretical concept that proposed by Lamarck to explain the mechanism of evolution is called lamarkism. Lamarck’s theory of evolution explains how evolution takes place by inheritance of acquired characters.
Lamrack’s Theory of Evolution:
Jean Baptist Lamarck known to history as chevalier de Lamarck, a French naturalist, former professor of zoology at jardandes plantes in Paris. In 1809 he published his theory regarding organic evolution in the book entitled philosophique zoologigue which later become well known as Lamarckism.
Principles of Lamarckism: Principles of Lamarckism or Lamarckian theory were based on four theoretical aspects of evolution of organisms. These are:
i. Internal urge of organisms
ii. Environmental change and new needs
iii. Use and disuse of organs
iv. Inheritance of acquired characters.
i. Internal urge of organisms:
Lamarck had the concept that:
i. Simple forms of living organisms are succeeded by more complex forms.
ii. The environment controls the organisms tending to made response to it.
iii. Organs vary in proportionality to the degree of its employment in which they are put.
Usually plants and animals tend to grow and increase in size. Not only the whole body but its each and every part increase in volume and size. According to Lamarck this increase in size is due to an urge or internal force of life and due to an inherent ability of organism itself. On the other hand it is due to desire or some sort of internal urge.
ii. Environment change and new needs:
On close examination of inter – relationship between organism and environment Lamarck understood that:
i. Environment is always in a state of change.
ii. The change in environment creates a new habitat.
iii. This new habitat exerts a profound influence on the body of organism, both in physiology and morphology.
iv. It brings about new needs for organisms which tend to survive in changed environment leading to new habit.
v. Thus change in environment brings about the development of new characters which results structural modifications and behavioral change in the organism, so that one organism develop adaptive features to co-op with new environment.
iii. Use and disuse of organs:
Lamarck was in the view that the organs of body which put to greater and more frequent use has tendency to grow and develop efficiently. Where as the organs which are less used or become use less in changed environment are reduced or vanished or remain vestigial.
For this concept Lamarck cited very good examples in various group of animals.
i. Lengthening of fore limb and long necking of giraffe due to its rapid grazing habit and gradual limitation of herb population tend to feeding on leaves of tall trees by extending the neck.
ii. Presence of vestigial limbs in python indicates the loss of preexisting limb in snakes.
iii. Degeneration of eyes in salamander and cave fish, proteus.
iv. Flightlessness in kiwi due to reduction of feathers and wings.
v. Wedded foot in aquatic birds is due to developing swimming habit.
vi. Biceps in hands in blacksmiths which put their hands constant to heavy hammering.
vii. Presence of appendix post anal tail and trace of nictitating membrane in man.
In this concern no examples implant was cited by Lamarck but reduction in different plant parts shows vestigeality and due to disuse. These include the following:
i. Reduction in number of petals and sepals in angiosperms.
ii. Reduction and modification in number of stamens and production of less number of pollens.
iii. Reduction introduction spores in bryophytes.
iv. Loss of motility structures like glagella in the gametes of higher plants.
v. Loss of flagella in unicellular algae like chlorella which present in chlamydomonas.
vi. Reduction in number of ovules and retaintion of single viable ovule in ovaries of gymnosperms and angiosperms.
iv. Inheritance of acquired character:
i. Environmental response leads to development of new adaptive characters in an organism through internal urge or through use and disuse of organs.
ii. Such characters are developed during the life time of an organism are called as acquired characters that not found in its immediate ancestors.
iii. Lamark was in the belief that the characters which are acquired by parental generation can be transmitted to the felial generations in the process of heredity.
iv. Therefore acquired characters are inherited leading to morphological and anatomical changes in a species lead to be evolved.
Thus Lamarckism holds the view that evolution taking place by the cumulative effect of environment on organism in relation to heredity over a long period of time.
This view of Lamarck was supported by some experimental evidences.
Criticism to Lamarck’s Theory:
i. Civier (1769 – 1832) who believed in theory of special creation, disapproved lamarkian theory demonstrating order changes in fossil.
ii. Weisman (1904) defines lamark’s view and rejected lamarkism by introducing germ plasma theory and he totally rejected use and dis-use of organ has any effect on evolution of species.
iii. Darwin did not considered Lamarckism but put emphasis on Mendelism and variation.
Taking to the views of the opponents of Lamarckism professor Giard and Cope (1840 – 1897), put Lamarckian theory into a new form called neo – Lamarckism. According to neo Lamarckism.
i. New needs create a new habit and the new environments create a new need, which play as the key point of evolution.
ii. Evolutionary changes involves the inter play of environmental factors, activity of organisms and inherited determiners.
iii. Evolution is the direct results of action of environment or the structure of organs and their relevant functions.