Reviewed by Kelly A. Hogan, University of North Carolina at Chapel Hill

From a BBC show called Bang Goes the Theory ( and shown on YouTube at

5 min and 28 seconds

A clever and simple analogy is made by Dr. Yan to show how evolution produces large scale diversity. Dr. Yan draws a perfectly straight line on a tablet computer. He then asks people at a large fair to trace the line with the computer pen. Each person that traces only sees the line that the previous person traced. Over time, the original straight line looks less like a line. He also shows how different branches of an evolutionary tree arise with the same line analogy.

I found Dr. Yan’s personality and entire video really engaging. The simple demonstration will stick with your students because it is a memorable analogy that is easily understood. This would make an excellent in-class activity too with stacks of tracing paper!

Do you think this is a useful analogy and would you show it to your students?