Biology · Chapter 19
Study notes aligned to the official NEB syllabus.
The process of organic evolution has been explained by different scientists by formulating different theories. The main theories are:
One of the first theories of evolution was published by Jean Baptiste Lamarck in 1809 in the book called Zoological Philosophy. His idea of evolution was based on the observation that changes in the environment lead to changed patterns in the species. His conclusions about evolution are as follows.
The internal forces of life tend to increase the size of an organism, i.e. the whole body and also its different parts, up to a limit which it brings about itself.
The production of a new organ in an animal body is the result of a need or want which has arisen and continues to be felt by the organism.
The continuous use of an organ makes it functional and strong and thus leads to its better development, while continuous disuse makes the organ undeveloped, weakened and finally disappeared. Example: giraffe.