In this article, I am concerned with the public engagements of Julian Huxley, Lancelot Hogben, and J. B. S. Haldane. I analyze how they used the new insights into the genetics of heredity to argue against any biological foundations for antidemocratic ideologies, be it Nazism, Stalinism, or the British laissez-faire and class system. The most striking fact—considering the abuse of biological knowledge they contested—is that these biologists presented genetics itself as inherently democratic. Arguing from genetics, they developed an understanding of (...) diversity that cuts across divisions of race, class, or gender. Human diversity rightly understood was advantageous for societal progress. Huxley, Hogben, and Haldane did not hold identical political ideals, but they all argued for democratic reforms and increased planning geared toward greater social equality, and they did so under the label of scientific humanism. Huxley took issue with the notion that evolutionary history does not carry any moral lessons for human societies. Rather than being its antithesis, evolution was the basis of human sociality. In fact, the entire future progress of individuals and communities toward a democratic world order needed to be founded on the cosmic principles of evolution—a process that had to be guided by the biological expert with a strong sense of social responsibility. (shrink)