__ causes gradual change in a species and leads to its evolution.

Natural selection:

1. The process by which modern organisms have descended from their ancestors, with changes in their allele frequencies, is called evolution.
2. Mutation, gene flow, genetic drift and natural selection causes the evolution.
3. Natural selection is a slow and gradual process which leads to the changes in the species or the formation of new species.
4. Some individuals with certain traits have higher survival and reproductive rate than others.
5. They pass on these genetic features to their offspring which brings an evolutionary change in the future generations.
6. This selection of the genetic qualities that prove beneficial for survival in future generations is known as natural selection.

Final answer: Natural selection causes gradual change in a species and leads to its evolution.