The theory of evolution explains how life on Earth has changed over time through natural processes. Here are its key principles:

## Core Concepts

**Common Descent**: All living organisms share common ancestors. Life began with simple forms billions of years ago and diversified into the millions of species we see today.

**Natural Selection**: Organisms with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits to their offspring.

**Variation**: Within any population, individuals have different traits due to genetic differences. These variations can be inherited.

**Gradual Change**: Evolution typically occurs slowly over many generations, though rates can vary.

## How Evolution Works

1. **Mutations** create new genetic variations
2. **Environmental pressures** favor certain traits
3. **Successful traits** spread through populations via reproduction
4. **Over time**, populations change and new species can emerge

## Supporting Evidence

- **Fossil record** showing progression of life forms
- **DNA similarities** between related species
- **Observable evolution** in laboratories and nature
- **Anatomical similarities** across species
- **Geographic distribution** of species

The theory doesn't address how life first began (that's abiogenesis), but rather explains how life diversified once it existed. It's the unifying principle of modern biology, supported by evidence from multiple scientific disciplines.
