Many secondary students hold misconceptions about evolution, even after instruction, that are often inconsistent with what is accepted by evolutionary biologists. Understanding evolution is difficult due to major conceptual difficulties concerning variation, differential survival, adaptation, and natural selection. In this article, the author discusses a specific pencil-and-paper activity which help students recognize the two distinct process in evolution by natural selection--the random production of variation and the nonrandom aspects of survival and reproduction. Thus, this activity is expected to help students combine their previous knowledge and build their own understanding of how evolution proceeds.