A scientific theory is a well-substantiated explanation of some aspect of the natural world that is based on a body of evidence and has stood up to repeated testing and scrutiny. It is more robust than a hypothesis and provides a framework for understanding observations and making predictions.

Evolution is the process through which species of organisms change over time through variations in their genetic makeup. These changes can lead to the development of new species.

Descent with modification explains that species change over time, give rise to new species, and share a common ancestor. This concept accounts for the similarities (shared traits from a common ancestor) and differences (adaptations to different environments) among species.