Edmund Beecher Wilson (19 October 1856 – 3 March 1939) was a pioneering American zoologist and geneticist. He wrote one of the most famous textbooks in the history of modern biology, The Cell.[1][2] Wilson was born in Geneva, Illinois, and graduated from Yale in 1878. He earned his doctorate at Johns Hopkins in 1881. He was a lecturer at Williams College in 1883–84 and at the Massachusetts Institute of Technology in 1884–85. He served as professor of biology at Bryn Mawr College from 1885 to 1891. He spent the balance of his career at Columbia University where he was successively adjunct professor of biology (1891–94), professor of invertebrate zoology (1894–1897), and professor of zoology (from 1897). Wilson is credited as America's first cell biologist. In 1898 he used the similarity in embryos to describe phylogenetic relationships. By observing spiral cleavage in molluscs, flatworms and annelids he concluded that the same organs came from the same group of cells and concluded that all these organisms must have a common ancestor. He also discovered the chromosomal XY sex-determination system in 1905—that males have XY and females XX sex chromosomes. Nettie Stevens independently made the same discovery the same year. In 1907, he described, for the first time, the additional or supernumerary chromosomes, now called B-chromosomes. Professor Wilson published many papers on embryology, and served as president of the American Association for the Advancement of Science in 1913. The American Society for Cell Biology annually awards the E. B. Wilson Medal in his honour.[3] 1902–1904: Theodor Heinrich Boveri (1862–1915), a German biologist, in a series of papers, drew attention to the correspondence between the behaviour of chromosomes and the results obtained by Mendel.[4] He said that chromosomes were "independent entities which retain their independence even in the resting nucleua... What comes out of the nucleus is what goes into it". In 1903 Walter Sutton suggested that chromosomes, which segregate in a Mendelian fashion, are hereditary units.[5] Wilson, who was Sutton's teacher, called this the Sutton–Boveri hypothesis.