Konstantin Sergeevich Mereschkowski (; – 9 January 1921) was a prominent Russian biologist and botanist, active mainly around Kazan, Tatarstan, whose research on lichens led him to propose the theory of symbiogenesis – that larger, more complex cells (of eukaryotes) evolved from the symbiotic relationship between less complex ones. He presented this theory in 1910, in his work, The Theory of Two Plasms as the Basis of Symbiogenesis, a New Study of the Origins of Organisms, although the fundamentals of the idea had already appeared in his earlier 1905 work, The nature and origins of chromatophores in the plant kingdom. Biography Early life Konstantin was born in Saint Petersburg, one of six sons and three daughters in the Mereschkowski family. His father Sergey Ivanovich served as a senior official in several Russian local governors' cabinets (including that of I.D. Talyzin in Orenburg) before entering Alexander II's court office as a privy councillor. His mother Varvara Vasilyevna (née Tcherkasova) was a daughter of a senior Saint Petersburg security official, and was fond of arts and literature. The writer Dmitry Merezhkovsky (1866–1941) was one of his younger brothers. From 1875 to 1880 he worked for his degree at the University of Saint Petersburg, travelling north to the White Sea to examine marine invertebrates and discovering a genus of Hydrozoa. On graduating he travelled to France and Germany, meeting famous scientists; he published on anthropology and animal pigments while in Paris. Career In 1883 he married Olga Petrovna Sultanova, and became a lecturer at the University of Saint Petersburg. In 1886 they emigrated from Russia for unexplained reasons, possibly connected to the acts of paedophilia for which he was later prosecuted. The family set up home in Crimea, where he found work as a botanist looking at varieties of grape; he also created a substantial collection of diatoms from the Black Sea. In 1898, he left his wife and young son in Crimea and emigrated to America, where he took the name "William Adler". He worked in California as a botanist at Los Angeles and University of California, Berkeley, devising a new system of classification of the diatoms based on the internal structures of the specimens in his Black Sea collection. In 1902, he returned to Russia to become curator of zoology at Kazan University; he became a lecturer there in 1904, and started to develop his ideas on the symbiotic origins of