Fact 1: Mutations are essential for evolution to occur.

Fact 2: Evolution causes species to change over time.

Given the two facts above, answer the question "The changes in species that have been seen over time required" with the following options: 
- Energy
 - exercise
 - strong microscopes
 - mutations
 - gene splicing
 - warm weather
 - vegetation
 - Energy.


 

    mutations     