In this chapter you will learn:
Definition of evolution
Concept of variation and its causes
Role of environment in variation
Important characteristics of Lamarck’s theory of evolution (Lamarckism)
Salient features of Darwin’s theory of evolution (Darwinism)
Comparative anatomy and artificial selection as evidences in support of evolution.
Almost two and a half million known kinds of organisms live on the earth today. Each others do not. A horse and donkey are similar in many ways, but each has some features not found in the other. Many of their features are not found in a dog, and each is very different from a frog or a lizard. The great variety of organisms leads to many questions, such as;
1. Why are organisms different? How did organisms obtain different features?
2. How can many different plants and animals live in the same environment?
3. Was the environment always same as it is now?
4. If each organism is suited to its environment; what happens if the environment changes?
5. Can organisms change along with their environment to survive?
6. Were the organisms existing today present in the same form in the remote past?
7. Will today’s organisms exist thousands of years after?
Because no one has direct knowledge about these questions, answers to them vary. Biologists attempt to find answers to such questions by using scientific methods that is investigations by means of observations, interpretation, hypothesis formation and experimentation.
As a result of scientific investigations biologists conclude that all the diverse forms of life that are now in existence have come into being through a gradual and continual process of modification of modification of ancestral forms. This “descent with codification” is known as evolution. Evolution does not lead to finished final product. The evolution modifies all living things and will continue to produce changes in the future also as it has in the present and past.
Category: 9th 10th