Species categories are not simply an invention of the human mind. Plants, animals, fungi, and viruses engage in "species making" by mingling and separating.1 Yet, at the same time, the boundaries that define or differentiate species are not simply "natural"; they are actively made, maintained, politically charged, and fashioned to serve some needs more than others, inviting new essentialisms even as they alert us to important differences. Like other rubrics for organizing social worlds—race, ethnicity, gender, age, ability—the concept of species and the alternative classifications it invites are complicated and controversial. Whether wild or domestic, pet or pest, such categories are subject to temporally fluctuating human motives, shifting values, and cultural diversities.