THEORY OF ORGANIC EVOLUTION -
CENTRAL THEME OF THIS THEORY -
1. INTERNAL VITAL FORCE -
Organisms and their organs have a natural tendency to continuously increase in size generation after generation, generally making them large and more complex.
2. DIRECT EFFECT OF ENVIRONMENT -
3. USE AND DISUSE OF ORGANS OR PARTS OF THE BODY -
The structure or organ which is in very frequent use become more prominent and highly functional as compared to the organs or structures that are less used.
The new structures are the acquired characters and less used organs are reduced and ultimately disappeared.
4. INHERITANCE OF ACQUIRED CHARACTERS -
The characters acquired by any species in its lifetime are inherited by the subsequent generations passed thereafter from generation to generations by hereditary factors.
(i) Giraffe -
(ii) Amphibians -
(iii) Birds -
(iv) Snakes -