When people hear the phrase "evolution is a theory," many assume it means evolution is a mere guess or speculation. This is a misunderstanding of what a scientific theory actually is. In science, a theory is not a guess, it is a comprehensive explanation of natural phenomena, rigorously tested and supported by a vast body of evidence. The evidence for evolution is overwhelming. Fossils embedded in layers of rock reveal a chronological record of life on Earth, showing gradual changes in species o