Thomas Hunt Morgan was born on September 25, 1866, in Lexington, Kentucky. As a child growing up in rural Kentucky, he was surrounded by nature and wildlife. Perhaps that environment contributed to his intense interest in biology, for Morgan later majored in zoology at State College of Kentucky. After his graduation in 1886, he investigated chemistry and morphology (the study of organism development to better understand evolutionary relationships) at Johns Hopkins University, completing his doctorate in 1890. From his graduate days on, Morgan believed that eredity was in some way central to understanding all biological phenomena--especially development and evolution. His persistence in trying to prove and develop heredity theories led to his winning the Nobel Prize for physiology or medicine in 1933.

In 1903, there were several attempts to explain variations in plants and animal species. One was Charles Darwin's theory of natural selection, a process by which organisms best adapted to local environments...