A backwards book? Eugenics and the evolution of R. A. Fisher’s <i>The genetical theory of natural selection</i>

R. A. Fisher’s 1930 book The genetical theory of natural selection has a mixed legacy. Its opening chapters are widely celebrated today for their role in revivifying Darwinism and laying the theoretical foundations of the so-called ‘modern synthesis’. Its closing chapters, meanwhile, are notorious. Across more than 100 pages, Fisher provides an extended meditation on eugenics and the decay of civilizations, past and present. The present article asks how this book of ‘two halves’ came to be. Drawing upon previously unstudied archival evidence, it reconstructs the authorship of this classic scientific text, overturning long-held ideas about the timing and order of the book’s composition. In so doing, the article sheds new and urgent light on a decades-long dispute regarding the relationship between Fisher’s eugenical commitments and his scientific contributions, at a moment in which his legacies are being actively debated once more.