Here's a breakdown:

* Changes in the structure of organisms: These changes refer to variations in physical traits, like beak shape in birds, or the presence of fur in mammals.

* Over a long period of time: Evolution is a gradual process that unfolds over many generations.

* Helps to explain many differences found in living things: The diversity of life on Earth is a result of evolution. Different species have adapted to different environments through these changes.

Key Concepts:

* Natural Selection: The mechanism driving evolution. Organisms with traits better suited to their environment are more likely to survive and reproduce, passing those traits on to their offspring.

* Adaptation: The process by which organisms evolve traits that increase their chances of survival in a particular environment.

* Genetic Variation: Differences in genes within a population provide the raw material for evolution.

Let me know if you have any other questions about evolution!