What did historical evolutionists such as Charles Darwin and Herbert Spencer have to say about music? What role did music play in their evolutionary theories? What were the values and limits of these evolutionist turns of thought, and in what ways have they endured in present-day music research? Theorizing Music Evolution: Darwin, Spencer, and the Limits of the Human is a critical examination of ideas about musical origins, emphasizing nineteenth-century theories of music in the evolutionist writings of Darwin and Spencer. Author Miriam Piilonen argues for the significance of this Victorian music-evolutionism in light of its ties to a recently revitalized subfield of evolutionary musicology. Taking an interdisciplinary approach to music theorizing, Piilonen explores how historical thinkers constructed music in evolutionist terms and argues for an updated understanding of music as an especially fraught area of evolutionary thought.In this book, Piilonen delves into how historical evolutionists, in particular Darwin and Spencer, developed and applied a concept of music that served as a boundary-drawing device, used to trace or obscure the conceptual borders between human and animal. She takes as primary texts the early evolutionary treatises that double as theoretical accounts of music's origins. For Darwin, music served as a kind of proto-language common to humans and animals alike; he heard the songs of birds and the chirps of mice as musical, as articulated in texts such as The Descent of Man (1871) and The Expression of the Emotions in Man and Animals (1872). Spencer, on the other hand, viewed music as a specifically human stage of evolutionary advance, beyond language acquisition, as outlined in his essay, "The Origin and Function of Music" (1857). These competing views established radically different perspectives on the origin and function of music in human cultural expression, while at the same time being mutually constitutive of one another.A ground-breaking contribution to music theory and histories of science, Theorizing Music Evolution turns to music evolution with an eye toward disrupting and intervening in these questions as they recur in the present.