Lamarkism Theory of Evolution
Definition : Theory of inheritance of acquired characters by ham ark can be defined as the variations/changes, developed in an organism (from normal characters) may be due to change in its surrounding environment or in the functioning (use or discuss) of organs, in its lifetime, to fulfill its new needs.
Or
As the time evolves, the organism changes and acquired certain new characters due to change in its environment organism also uses or discuss its organs in order to fulfill its new needs.
Introduction : Lamarkism also called “ Theory of inheritance of acquired characters”. It was proposed by Lamark – a fresh evolutionist (1744-1829) He published his theories in 1809, in his book ‘Philosophique Zoologique’
Postulates/essentials of his theories are :
- Growth : Every living organism tends to increase the volume of its body and hence the size upto a certain limit.
- Production of a new organ as a result of need : This production occurs as a result of a new need inside the body that is felt continuously by the animal.
- Use and disuse : The development of an organ is directly proportional to its use. It an organ is used continuously and constantly, it will tend to become highly developed whereas continuous disuse brings about its extinction.
Also called Lamarkin Doctrine.
- Inheritance of Acquired Characters : All the changes and modifications are acquired by individuals during the lifetime of an individual are transmitted to its offspring i.e. are inherited. These inheritable characters accumulate over a period of time resulting in a formation of new species (speciation).
‘Lamarkism’ was exemplified by studying stages in the evolution of present-day giraffe. Development of present day-long – necked and long for – limbed giraffe from the deer-like ancestor by the gradual elongation of neck and forelimbs in response to the deficiency of food on the barren ground in the dry deserts of Africa. These bodies were elongated so as to eat the leaves on tree branches. This shows, how giraffe elongated his neck by extra use of the organ.
OBJECTIONS :
Weismann’s mutilation experiment :
Weismann mutilated/cut the tails of white mice but their offsprings did not show any reduction of tails – he performed this act for five successive generations, in all 901 mice’s tails were cut – but none had a vestigial tail.
This shoved that every change in body organ is not inherited.
Indian Tradition :
Piercing of ears and nostrils has continued since continues in human beings, but never have the offsprings born with any holes in their ears/nostrils
Conclusion : Objections and evidence confirm the theory on the inheritance of acquired characters as unconvincing and unsatisfactory. So Lamarkism was rejected.