On 5 April, Darwin sent Murray the first three chapters, and a proposal for the book's title. An early draft title page suggests "On the Mutability of Species". Murray cautiously asked Whitwell Elwin to review the chapters. At Lyell's suggestion, Elwin recommended that, rather than "put forth the theory without the evidence", the book should focus on observations upon pigeons, briefly stating how these illustrated Darwin's general principles and preparing the way for the larger work expected shortly: "Every body is interested in pigeons." Darwin responded that this was impractical: he had only the last chapter still to write. In September the main title still included ""An essay on the origin of species and varieties"", but Darwin now proposed dropping "varieties".