Explain through Darwin's Theory of evolution how species become better adapted to their environment.

Darwin's Theory suggests that all populations have variation between them, this variation is primarily caused by mutations in DNA. If an individual within a species gains a beneficial mutation it will be more likely to survive when competing against others of it's own species e.g. for food. Those that survive will be able reproduce, passing on the beneficial mutation to it's offspring, so this mutation becomes more common in the following generations and the species as a whole becomes better adapted to competing in its environment.