Hernán uses a retrospective approach to address a broad range of questions in the evolution of plants and their pathogens. This approach gains its power from obtaining direct observations from the past through sequencing historical and ancient samples, and combining them with present-day genomic information. Hernán has pioneered the use of herbarium specimens and plant archaeological remains for evolutionary genomics studies using standards and techniques akin to the ones that have been successfully used in human ancient genomics. Hernán has studied organisms as diverse as modern humans, ancient hominins, plants, and plant and animal pathogens. Currently, Hernán’s research focuses on three main topics: the dynamics of past plant-pathogen epidemics; the identification and timing of key events in crop domestication and the spread of agriculture; and the colonization of new ecological niches by invasive/introduced species.