Here is a fine way to spend 16 minutes. A wonderful (even if simplified) story of a gene at the top of the hierarchy of limb formation in tetrapods, and the identification of a mutation in the gene that causes a dramatic change in fish's morphology. It is remarkable that the mutation doesn't affect the protein sequence but the switch that turns it on or off in different tissues of the developing animal. Why would this be of particular interest to you? Because shown herein is the remarkable correlation with the fossil record of this small fish. So grab some popcorn, or better yet a beer or glass of wine and enjoy yet another page of how scientific research illuminates.