Ridley concentrates on understanding Darwin's most important books, On the Origin of Species and The Descent of Man, but he also examines a sample from one of Darwin's other works on the emotions, as one representative from Darwin's lesser-known works that ranged from flower pollination to coral reefs, from animal domestication to landscaping by earthworms.

Mark Ridley works in the Department of Zoology, Oxford University. He previously held posts at Emory University in Atlanta and at Cambridge University in England. His books include the standard college text Evolution and Mendel's Demon. He has also edited anthologies on Evolution and A Darwin Selection.