Our unprecedented times go by various names—posthuman, post-postmodern, the Anthropocene—each of which breaks decisively with the alleged stupidities of the nineteenth century and its dreams of human mastery and progress. In response, this book excavates from nineteenth-century British thought various “subversive humanisms” that complicate the intellectual genealogy of critical posthumanism without losing sight of historical context.Using new and neglected sources, it brings together well-known figures such as the liberal utilitarian John Stuart Mill and the positivist Henry Buckle, as well as lesser-known philosophers, scientists, and poets, including Constance Naden, Julia Wedgwood, May Kendall, Henry Stephens Salt, and Edward Carpenter. In different ways, these thinkers subverted from within the epistemological, ontological, and historical premises of nineteenth-century humanism. Their reflections on evolutionary becoming, anthropocentrism, scales of historical time, and humanity’s relationship to the natural environment demonstrate the ways in which thinking about time ontologically constituted “the human”—a question that is central to today’s posthuman predicament.By tracing these debates in their unfolding complexity, the book demonstrates that critical posthumanism cannot and should not attempt to transcend humanism entirely. Instead, it must deconstructively inhabit humanism’s troubled and elastic history, finding unexpected resources in the very historical moment—the nineteenth century—that it seeks to escape.