Lamarckism

Theory of Lamark (Lamarkism)

• French naturalist Lamark said that evolution of life form had occurred but driven by and disuse of organ.

• Book- philosophae Zooiogique

• Actual theory of Lamark- Inheritance of acquired character and was based on use and disuse     of organs.

• Lamark explained his theory on following points-

                (a) Tendency to increase in size

                (b) Direct effect of environment

                (c) Use and disuse of organs

                (d) Inheritance of aquaired character

Examples for Support of His theory

(I) African Giraffe- Elongation of neck and passing this acquired character to succeeding generation

(ii) Snakes- Gradual degeneration and disappearence of Limbs.

Supporter of Lamarkism

   (i) Exp. of Sumner on Rat- He reared and domesticated rats for many generation in two different environmental condition -

• Rat of Hot environment- Tail and ear pinnae enlarged and this acquired character passed in to next generation (Inherited)

         • Rat of cold environment- Tail and ear pinnae shortened and this acquired character passed in to next generation (Inherited)

   (ii) Exp. of Kammerer on Salamander -    Salamander is a tail less amphibia (Apoda) with black-    yellow patches on skin. Cammerer reared and domesticated in two different environment.

          • Salamander of Dark environment- Black patches of skin enlarged and this aquaired character passed on succeeding generation.

          • Salamander of yellow environment illuminated by yellow light- Yellow patches of skin        enlarged and this acquired character Passed on next generation.

         • Specific- Once Kingsle Nobel visited to Kamerer lab and after inspection he found that Kamerer injected yellow dye bellow the skin of salamander. That was the reason to enlarge yellow patches. Because of shame and guilt he finally commit to suicide.

(iii) Exp. of Mc. Dougal on Rat- He trained rats to move through particular path and need of training gradually become insignificant in successive generation

(iv) Exp. of Pavlov on Dogs- Same as conditional reflex experiment.

Criticism of Lamarkismi  (by Weismann)

1. Weismann was the great criticizer of theory of use and disuse or inheritance of acquired   characters

2. Germplasm Theory given by Weismann in order to disprove the theory of use and disuse or  inheritance of acquired characters.

         Germaplasm (Immortal) — Sperm+ova (changes Reaches to next generation)

         Somatoplasm(Mortal)— Either than gametic cells (Changes will  reach to next generation)

 3. Experiment: Weisman experimented on white mouse he continued cutting the tile of new born mice for many generations, yet there was no hereditary effect even upon the length  of tail.

                                                Neo-Lamarkism

Some modification made in Lamarkism and represented as following—

"Genetic or chromosomal changes may occurs due to change in environment or use and disuse. There changes effects some physical and chemical changes in germplasm means to leads to change in genes of germplasm and reaches to next generation."

Ex. Potato Beetle           ^X-rays          Change in genetic material of germplams such  changes passes to next generation       ^Cosmicrays