Explain why fossils are important as evidence for the theory of evolution by natural selection. Include in your answer a reason why the fossil record is incomplete.

Fossils are the preserved remains of organisms that lived millions of years ago, so they give a direct record of past life.
They show how organisms have changed over time – for example, the gradual change in the shape of the horse’s teeth and limbs, which demonstrates evolutionary change.
However, many organisms do not become fossils because soft bodies decay completely or do not leave hard parts that can be preserved.
Because of this, the fossil record is incomplete, making it difficult to trace the full evolutionary history of all species and leaving some transitional forms missing.