Why do we look like our parents? We inherit particular versions of genes that shape our growth. For a long time these genes were unknown and it was suspected that each class of animals would have distinct “designer genes.” Explosive progress has identified hundreds of genes that work together to shape animal growth, sculpting their tissues and organs, even the instincts embedded in brains. Surprisingly, scientists have found that many designer genes have been highly conserved during evolution. Some genes play similar roles, like controlling heart or eye development, in diverse animals. Different animals use related genes for related purposes because their common ancestors did. Damage to the designer genes can lead to birth defects, cancer, and neurodegeneration, so exploring how body-shaping genes function leads to new types of medical diagnosis and treatment.