Topic Darwin’s Theory of natural selection There are a few theories that attempt to explain or show how organisms change (evolve) over time .ee
1.The Branching Theory.
2.The Theory Of Spontaneous Generation.
3. Use And Disuse.
4.The Theory Of Natural Selection.
Darwin’s theory of natural selection proposed that nature(the environment) is a major contributing factor of evolution.In other words organisms with traits that help them survive in a changing environment ,will reproduce and pass on their traits to the next generation.A logical sequence of ideas explain this theory.
the power point presentation will help you understand how species change over time
Also you may read about the other proposed theories,check these links:
you know that ,Darwin could not explain the genetic basis of variations.