• Inheritence of Acquired Characters: The characters acquired by one generation are transmitted to the new generation and subsequently newer characters are added in next generation to acquire perfection.

This, lemarcks proposed that evolution is a slow process where characters are acquired over the course of time in various generations.  
Explanation of theory with observed evolution:  Lemarck inhis book explained the evolution of various animals to elaborate the proposed hypothesis.

1. Giraffe: Lemarck uses his hypothesis to explain the appearance of Giraffe with long neck and forelimbs. The different evolutionary stages of present giraffe is explained as per lemarck theory in figure 7.1. As per the theory, the giraffe is evolved from the short height deer like ancestor. These ancesters are living in the barren place with leaves on the trees available to them for eating. In order to reach the leaves on tree, it streacted its neck and forelimbs. As a result, these organs get elongated. These acquired character in first generation passed on to the subsequent generation and continuous streatching accumules this character over the course of few generations to evolve giraffe with long neck and forearms.

 

Figure 6.1: Event in the evolution of giraffe from deer link ancestor.