Central to their argument is a re-reading of Darwin's over-looked and misunderstood The Descent of Man, published in 1871. Buoyed by the success of the Northern States in the recent Civil War, it was only now that Darwin finally felt able to publish compelling evidence that the "separate races" theory, which had under-written African slavery on American soil, was bunkum. Far from being a distinct, and potentially inferior, species, the black man (and, indeed, the brown, yellow and red one too) was the literal brother of the top-hatted Anglo-Saxon.

Ironically, the Anglican clergy who had been so appalled by the way that Origin of Species had dismantled Genesis over a decade earlier had been closer to the evolutionary truth than they might have liked to believe. We were all, it turned out, descended from a metaphorical Adam and Eve.

Desmond and Moore have written a stunning book, deftly incorporating new sources without becoming clunky. Just as importantly, they demonstrate biography's usefulness as a way of understanding the history of ideas as an embodied phenomenon. For all that "Darwinism" had become an over-arching system by the 1930s, it was still the product of one man's mind, a man with a bad stomach, a cultural aversion to slavery, and a lapsed Anglican's belief in the spiritual equality of all men. It was out of this particular nexus that Darwin pursued his investigations into the origins of life, and it is only by paying proper attention to it, suggest the authors, that we can avoid the kind of ahistorical fallacy in which a man born 200 years ago somehow becomes a cheerleader for Hitler's Final Solution.