The theory of evolution says that living things change over generations, and that all species are related through common ancestry.

The basic ideas are:

- **Variation:** Individuals in a species are not exactly the same. They differ in traits.
- **Inheritance:** Some of these traits are passed from parents to offspring.
- **Natural selection:** If a trait helps an organism survive or reproduce, individuals with that trait are more likely to leave offspring. Over time, that trait can become more common.
- **Mutation and other genetic changes:** New variations arise through mutations and genetic processes.
- **Descent with modification:** Over long periods, small changes accumulate. Populations can become so different that new species form.

So evolution does **not** say that one modern species “turns into” another modern species overnight. Instead, it says populations gradually change over many generations, and different species can share common ancestors.

For example:
- Humans and chimpanzees did **not** come from each other.
- Rather, they share a common ancestor that lived long ago.

In short, evolution is the scientific explanation for the diversity of life on Earth: life changes over time, species arise from earlier species, and all organisms are connected by branches of common descent.
