Archibald Garrod (1857–1936) was a British physician who became interested in a rare but harmless disease called alkaptonuria. A unique characteristic of this condition is that the patient’s urine turns black when exposed to air. Previously, physicians thought the disorder was due to a bacterial infection; however, Garrod observed that the disorder was more common in children of first-cousin marriages and followed the Mendelian description of an autosomal recessive disease. Garrod, a follower of the then fledgling science of biochemistry, suspected that the urine turned dark because patients lacked the enzyme to break down the protein that caused the urine to darken. He referred to alkaptonuria as an inborn error of metabolism. Unfortunately, very few people understood metabolic pathways at that time, so his contributions remained largely unnoticed. By the 1950s his work was verified, earning Garrod the title of “father of chemical genetics.”