On the Origin of Species in its 6th edition, earning Darwin nearly £3000.) 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
On the Origin of Species America, Africa, and Australia all have regions with similar climates at similar latitudes, but those regions have very different plants and animals. The species found in one area of a continent are more closely allied with species found in other regions of that same continent than to species found on other continents. Darwin noted that barriers to migration played an important role in the differences between the species of different regions. The coastal sea life of the Atlantic and Pacific sides of Central America had almost no species in common even though the Isthmus of Panama was only a few