Clicker Question Considering only vertebrate animals, evolution by natural selection can occur on which of the following time scales? A) Decades B) Centuries C) Millennia D) All of the above E) B and C only Answer: D This is an optional pre and post assessment clicker question that can be integrated into the main PowerPoint. This question addresses the common misconception that natural selection only works on longer time scales. This case study is a dramatic example of evolution occurring over a 30 year period.