The evolution is explained by principles of the natural selection is as follows:
1. Resources are scarce
2. There is a biological variation within all species.
3. There are more born that the available resources, hence competition.
4. Adaptation to the environment will likely aid survival
5. Environment will decide which is deemed fit
6. Those who are considered fit will have offspring, and those who arent will die out.
7. As time goes on, those with more successful adaptation will develop more mutation, later becoming a new specie.
When applied to the theory of evolution, our primate ancestors have developed mutation that were deemed more fit, thus creating a separate species that evolved to human beings.