3. __INTRODUCTION__
• 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.
5. 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.
6. 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.
7. 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.
8. EXAMPLES OF LAMARCKISM
• 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.
9. NEO- LAMARCKISM
• IT IS A MODIFICATION OF THE ORIGINAL THEORY OF LAMARCK IN ORDER TO
MAKE IT MORE SUITABLE TO MODERN KNOWLEDGE
• THE THEORY STRESSES ON THE DIRECT EFFECT OF CHANGED ENVIRONMENT ON
THE ORGANISMS.
• ONLY THOSE MODIFICATIONS ARE TRANSFERRED TO THE NEXT GENERATION
WHICH INFLUENCE GERM CELLS OR WHERE SOMATIC CELLS GIVE RISE TO GERM
CELLS.
• NEO-LAMARCKISM DOES NOT GIVE ANY IMPORTANCE TO THESE FACTORS.
10. THE VARIOUS PROPOSITIONS OF NEO-
LAMARCKISM ARE
THE DRIVING FORCE FOR EVOLUTION IS THE ENVIRONMENT.
CHANGE IN THE ENVIRONMENT BRINGS ABOUT CHANGES IN THE HEREDITY OF
THE ORGANISMS.
A NUMBER OF VARIATIONS APPEAR IN THE ORGANISMS. AT LEAST SOME OF THE
VARIATIONS ARE TRANSFERRED TO THE NEXT GENERATION.
VARIATIONS PASSED ON TO THE PROGENY ARE THOSE WHICH INFLUENCE GERM
CELLS OR THE GERM CELLS ARE FORMED FROM THE AFFECTED SOMATIC CELLS.
