Proc. Natl Acad. Sci. USA doi: 10.1073/pnas.0803851105 (2008)

Why haven't oncogenes — genes that cause cancer — been eliminated by natural selection? André Fernandez and a colleague from Ohio University in Athens believe they have found a possible answer. In a species of swordtail fish, Xiphophorus cortezi, the oncogene Xmrk also causes a dark pattern on male fish's tail fin that females in two out of three populations studied found attractive. Indeed, fish that have developed cancer had the largest patterns and were able to mate for many months before the disease killed them.