Warner joined the WildCru in 1987, as part of the Wytham radio-tracking team. Originally carrying out field research on African elephant projects with Dr Malcolm Coe, and another with Prof. Phyllis Lee and Cynthia Moss, he ultimately pursued his DPhil with Prof David Macdonald on evolutionary epidemiology, cooperation, and communal care in animals, primarily through a long-term investigation of sexual selection and reproductive tactics of free-ranging, group-living domestic cats. He connected WildCru to Dr. Stephen J O’Brien and the National Cancer Institute, USA, pursuing DNA fingerprinting to identify paternity, disease dynamics, and felid reproductive physiology. He also helped develop an evolutionary theory that became known as the ‘immunocompetence handicap hypothesis’. Since 1992, he has been engaged as a leader in international humanitarian management.