William Ernest Castle was one of the earliest experimental geneticists. Castle helped extend the application of Mendel's Laws to mammals, and was one of the first to link Mendel's ideas with Darwinian natural selection. While he often found himself on the losing side of scientific debates, Castle's straightforward and honest approach to the new science of genetics made him well respected by colleagues and students.

From his early days growing up on a farm, Castle showed a strong interest in natural history. He collected wild flowers, learned to graft trees, and to identify the bones of various animals. Castle's first degree, from Denison University in 1889, was in Classics. However, his interest in biology was furthered by a teacher who taught him Darwin's theories of evolution, despite strong theological opposition to such classes. Upon graduation, Castle became a Classics teacher at Ottowa University, Kansas, but also published his first...