Of the endless variety of behavior that has evolved to assist animals in finding and securing mates, one of the most unique adaptations is monogamy, a mating system characterized by prolonged pair-bonds and often, bi-parental care of offspring. While common among birds, monogamy is rare (but present) in fishes, mammals, non-avian reptiles and amphibians, and even some invertebrates. In our lab, we try to understand the proximate and ultimate forces that have driven the evolution of monogamy and how these forces continue to act. Specifically, we study how inter- and intra- sexual selection interact in the formation of pair bonds and what role steroid hormones play in this process.