Lewis I. Held, Jr is a fly geneticist who has taught human embryology for 30 years. He studied molecular biology at the Massachusetts Institute of Technology (BS, 1973), investigated bristle patterning under John Gerhart at the University of California, Berkeley (PhD, 1977) and conducted postdoctoral research with Peter Bryant and Howard Schneiderman at the University of California, Irvine (1977–86). Deep Homology? is his fifth scholarly monograph, following Models for Embryonic Periodicity (1992), Imaginal Discs (Cambridge, 2002), Quirks of Human Anatomy (Cambridge, 2009) and How the Snake Lost its Legs (Cambridge, 2014).