Capel is a leader in the field of vertebrate sex determination. She pioneered the bipotential gonad as a model for studying cell fate commitment and organogenesis. She discovered that in mammals, canalization of testis versus ovary development depends on the balance between two antagonistic signaling pathways. She was the first to trace the origin of somatic cells in both organs and to show that the vascular supply regulates testis morphogenesis. Recently, she established a direct link between epigenetic regulation and temperature-dependent sex determination in reptiles. She has a distinguished track record in promoting basic research to the lay public.