For years scientists have recognized that the Sea of Cortez, the long sea that sits between mainland Mexico and the Baja California peninsula, has been home to many species of marine animals that are found nowhere else on earth. I'm interested in how and why this relatively small area of the ocean is home to so many unique species. In order to learn more about this, I study a type of fish called a mudsucker to see how its genes have changed over time. These changes can be caused either by natural selection or from the physical separation of different individuals of the same species. To figure out which processes may be most important in the Sea of Cortez, my work looks at patterns in the DNA sequence of mudsucker genes to see how and when different species of mudsucker have formed over time.