A key figure in the field of evolutionary biology, William Bateson (1861–1926) revived Mendelian methods of analysis to develop Darwin's theory of evolution, thereby pioneering the study of genetics. In these lectures, published at Yale in 1913, Bateson systematically chronicles the era's conflicting and developing theories on taxonomy, speciation, variation and hybridisation, and includes his own thoughts on continuous and discontinuous variation and its causes. Drawing on the comparative physiology and anatomy of species that he knew from his wide experience, citing detailed examples from across the taxonomic kingdoms, Bateson brings to life this exciting time in biology. Because the theories central to the modern understanding of genetics, heredity and evolution were formed at this time, this work remains valuable and relevant to students of biology and the history of science.