Desmond and Moore's earlier biography, "Darwin", is one of my favourite books, so I was really looking forward to reading "Darwin's Sacred Cause". But I have to say that I am not convinced by the central thrust of this book.
Charles Darwin was very strongly opposed to slavery, and he argued, quite rightly, that all human beings are of one species with a common ancestry. He was very critical of the mistaken theory that the different "races" of humans came into existence separately as separate species.
What Desmond and Moore claim is that Darwin's theory of common HUMAN origins inspired the development of his view that ALL LIFE is related by common descent through evolution. The "sacred cause" of opposition to slavery inspired Darwin's science.
But in his autobiography, which was initially written for private, family consumption, Darwin nowhere says anything about his anti-slavery views influencing his evolutionary theories. In fact Darwin explicity says that it was the distribution of fossil and living species which he encountered on the Beagle voyage that first got him seriously thinking about evolution. (Though I suppose that Desmond and Moore would say there was an underlying, unstated influence.)
There is also the fact that even if Darwin's anti-slavery views influenced his theory of the common origins of all life, it certainly was not a factor in inspiring him to come up with his theory of natural selection as the mechanism for evolution. It was natural selection that was Darwin's most important idea, and both he and, later, Wallace were inspired to come up with the theory by reading Malthus on population. (It is ironic that Malthus could be so reactionary and wrong about human population and society, and yet inspire a correct theory of natural selection.)
I find it quite plausible that Darwin's anti-slavery views were ONE influence on his evolutionary theory of life's common ancestry. But Desmond and Moore are overstating their case when they argue that it was THE influence on his theory.
In their earlier biography Desmond and Moore did a wonderful job of putting Darwin in the context of Victorian society. In this book they have homed in on one aspect of Darwin's social and political world, made a lens out of it, and then looked at everything through that lens, thus giving a distorted picture of a more complex reality.
This book is certainly worth reading - but with a critical eye. And for an alternative view of how Darwin's ideas developed, I recommend Niles Eldredge's book, "Darwin: Discovering the Tree of Life".
Phil Webster.