The title of Garrod’s landmark report on the first of his inborn errors of metabolism was “The Incidence of Alkaptonuria, a Study in Chemical Individuality.”34 By “incidence,” he meant occurrence, and, in the work, he referred particularly to the role of parental consanguinity. In one short work, he identified consanguinity as a prime factor in the occurrence of rare recessive disorders and introduced his concept of chemical individuality.