Volotskoi’s ‘Marxist’ critique of Galtonian eugenics, his concept of ‘bio-social’ eugenics, and Florinskii’s ideas that underpinned them. This time, actively popularized by Volotskoi, Florinskii’s treatise proved influential in shaping discussions on the agendas and directions of eugenics and its ‘stepsister,’ genetics, in the Soviet Union, especially the heated debates over the possibility and necessity of creating a distinct ‘proletarian,’ ‘socialist,’ ‘bio-social’ eugenics. It also informed certain policies on marriage and family adopted by the Soviet authorities, including the promulgation of new laws on ‘the protection of health of prospective spouses and their progeny’ and the establishment of ‘marriage consultations.’ If Volotskoi and his like-minded colleagues did not succeed in creating ‘bio-social’ eugenics based on Florinskii’s ideas, it was certainly not for the lack of trying. But just four years after the republication of Florinskii’s treatise, in 1930 eugenics was condemned in the Soviet Union as a ‘bourgeois,’ ‘capitalist,’ ‘fascist’ doctrine. The Russian Eugenics Society dissolved and any references to Florinskii’s treatise vanished from the public scene. A peculiar amalgam of ideas, ideals, concerns, and practices embedded in the very notion of eugenics broke apart. In the next few years, the issues of ‘human perfection’ lost their ‘hereditary component’ and were relegated to the purview of social hygiene, physical and general education, psychology, and pedagogy. At the same time, the problems of ‘human degeneration’ were reduced to ‘hereditary diseases’ that became the subject of a new discipline—medical genetics—established and actively developed by several former members of the now defunct Russian Eugenics Society. During the Great Terror of the late 1930s, however, the institutional base of medical genetics was destroyed. A decade later, in 1948 the entire discipline of genetics was banned in the Soviet Union, as the result of a vicious campaign waged by the notorious agronomist Trofim Lysenko and endorsed personally by the ‘Great Teacher’ Joseph Stalin. In light of these events, it seemed that Florinskii’s treatise was destined to gather dust in some remote library storage forever. But Fate is a fickle mistress. Shortly after Stalin’s death, during the de-Stalinization campaign launched by his successor Nikita Khrushchev in the 1950s and popularly known as the Thaw, medical genetics re-emerged in the Soviet Union. A decade later, both Galton and eugenics were ‘rehabilitated,’ and with them Florinskii and his book re-entered Soviet discourse on human reproduction, heredity, variability, development, and evolution.