Nikolai Ivanovich Vavilov proposed theories of plant genetic diversity and participated in the political debate about genetics in Soviet Russia in the early twentieth century. Vavilov collected plant species around the world, building one of the first and most comprehensive seed banks, and he spent much of his life researching plant breeding and genetics. Vavilov also developed a theory of the historical centers of origin of cultivated plants. Vavilov spent most of his scientific career in Russia, although he studied abroad and traveled extensively. The ascent of geneticist Trofim Lysenko, favored by Joseph Stalin, and Vavilov's public criticism of him lead to Vavilov's arrest in 1940 and his death in prison three years later.