Why do humans have precisely 5 fingers and toes? How does a bone know to stop growing when it reaches the appropriate length? What controls our biological sex? While the human genome successfully encodes the information required to produce a “normal” human being, genetic variation dictates the subtle and not so subtle differences that make us each a unique individual. “Mutant” humans throughout history have provided insights into how genetics underlie development by showing us what can happen when the delicate balance of genes and their proper expression is perturbed. This course will focus on the history and the science behind some of the more pronounced human “mutants” including conjoined twins, dwarfism and giantism, and progeria (rapid aging), to name a few.