Within biology, the idea that a species or a type of organism a contains an “essence” that makes them what they are (e.g., that dogs are all dogs because they carry the essence of “dogness”). Since essences don’t change over time, essentialist perspectives don’t cohere with evolutionary history, in which the traits of lineages change over time and single-celled ancestors evolved into multi-celled microrganisms, and these in turn diversified into the wide variety of species that have inhabited Earth over life’s history.