Darwin's Sacred Cause

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Adrian Desmond and James Moore, Allen Lane, £25

This year marks the 150th anniversary of the publication of one of the most important scientific works of all time, Charles Darwin's On the Origin of Species. This book transformed the way we see not just ourselves, but all life on earth. There are two "big ideas" in Darwin's theory of evolution. One is that there is a tree of life; according to this idea all the different forms of life on earth have a common ancestor. The other idea is that of natural selection; this is, roughly, the claim that certain characteristics become more prevalent because they make organisms better suited to the environment in which they find themselves.

But how did Darwin come up with these ideas? One view is that he was a hard-headed scientist doing detached hard-headed empirical science. However, in Darwin's Sacred Cause, Adrian Desmond and James Moore (who also wrote the highly acclaimed Darwin) claim that this is not in fact the case.

Desmond and Moore argue that to understand why Darwin started thinking about the origins of species we have to appreciate his moral anchorage in the high tide of the British anti-slavery movement. Darwin's family and many of his friends actively campaigned for the abolition of slavery and Darwin himself abhorred it. The abolitionists argued that blacks were not "subhuman", or beasts to chain, but rather they formed part of the unity of the human race. The anti-slavery tracts that Darwin read and his family distributed implied a single origin for black slaves and their white masters, a shared ancestry.

Desmond and Moore's proposal is a striking one not only because it recognises that a researcher's personal and social milieu affects their findings but also because it suggests that one of the most important scientific theories ever was developed in response to a disgust with slavery and a belief in the unity of humanity.

However, I am not fully convinced by the account offered for two reasons. The first is that if a moral passion was indeed firing Darwin's account of evolution, why then - as Desmond and Moore themselves note - is there next to nothing about human origins in On the Origin of Species? If his abhorrence of slavery is what drove his account of evolution, why does he not mention the unity of humans? The second is that, even if Desmond and Moore are correct, their account offers no explanation about the origins of the second of Darwin's big ideas, namely, natural selection.

In short, Desmond and Moore's proposal is fascinating (if lengthy) but ultimately it is not totally convincing.