Symbiogenesis, a term first coined by the Russian botanist K.S. Merezhkovsky in the late 19th century, is the evolution of new life forms, from the physical union of different, once-independent partners. In this book Liya Khakhina traces the development of the concept in Russian and Soviety scientific literature, reviewing the contributions of Merezhkovsky, A.S. Famintsyn, B.M. Kozo-Polyansky and other prominent Russian scientists, to theories of symbiosis in evolution. This book provides further information to English-speaking scientists on the history of the early development of symbiosis theory. The editors have written an introduction to Khakhina's book (published in the Soviet Union in 1979) and have also included an appendix by Donna Mehos about the American anatomist Ivan E. Wallin, whose theory of symbionticism - species origin by the acquisition of microbial symbionts - resembled the theories of the Russians.