I used to enjoy eating barbecued octopus. Peter Godfrey-Smith has spoiled it for me. I know now that an octopus is fearfully and wonderfully made, just as the Psalmist tells me I am, and so to eat it seems like a kind of cannibalism.

It can squeeze through a hole the size of its eyeball. Its oesophagus tunnels through its brain, and the brain is sometimes skewered by a spiky mouthful of food. It smells and tastes with its arms, sees with its skin, plays with toys and craves novelty. It can turn off lights by squirting water at them, negotiate mazes, undo jam jars from the inside, carry round two halves of a coconut shell and assemble a house from them wherever it stops, and recognise individual human keepers, even when the keepers are wearing identical uniforms. In many ways octopuses are like toddlers. They’re even petulant. One captive octopus wanted to demonstrate its resentment at being fed second-rate food. It waited until it knew the keeper was watching before contemptuously dumping the food down the drain.

Yet my qualms about eating octopus cannot stem from biological kinship. The last common ancestor of myself and the octopus lived around 750 million years ago and was, possibly, a small, flattened worm. Cephalopods are a highly successful experiment in the building of large brains, but one wholly independent of that which produced Mozart and partial differential equations. They have radically different kinds of bodies and minds to ours. Evolution decreed that most of our neurons should cluster in a ball in our head, but while cephalopods do have a brain, most of their neurons are in their arms. Those arms are like Wales: they have a mysterious autonomy from the neuronal metropolis. An arm that has been cut off can still reach and grasp. Godfrey-Smith puts it memorably: ‘In the octopus’s case there is a conductor, the central brain. But the players it conducts are jazz players, inclined to improvisation.’ Simple mind–body dualism isn’t a philosophical option if you’re an octopus.

Such wondrous creatures deserve a remarkable chronicler. They’ve found one in Godfrey-Smith, a man who swims elegantly, scuba tank on his back, through neurobiology, philosophy of mind, evolutionary theory and a strange meeting point for octopuses, fifty feet down, off the east coast of Australia.

Other Minds contains the best concise account of the origin of animals I’ve read. His inquiry into the complexity of cephalopod behaviour is a crystalline delight. Yet the clarity that is such a virtue in the early chapters becomes a curse when he starts to grapple with the origin of consciousness. Where the evidence justifies only a verdict of uncertainty, a definite verdict is a miscarriage of justice. It is mere fundamentalism to frame mysteries as certainties and to force ineffabilities into strident propositions.

The fact, embarrassing or exciting depending on your point of view, is that no one has the faintest idea what consciousness is for, and hence why it should have erupted so incontinently throughout evolutionary history. You don’t need it for theory of mind; you don’t need it for the type of communitarianism that plainly confers a selective advantage. It’s apparently useless for anything that is visible to natural selection. Godfrey-Smith is a thinker of great power and intellectual courage. It’s simply not good enough to imply that consciousness is a type of substance that starts to be secreted when you have a critical mass of neurons.

Several passages reminded me of Talmudic discourse. There the overriding concern is to offend neither Torah nor the eminent sages who have opined before. This is often supremely difficult, and the Talmudists’ efforts are exhilarating to watch. So it is here. Godfrey-Smith’s efforts sometimes have a dated and defensive air. He has a Dawkins-esque desperation to squeeze the facts into a neo-Darwinist paradigm and there is a corresponding failure to mention anything that falls outside it. We now know that evolution isn’t just the scream of the prey, the moan of the out-competed and the grunt of completed ejaculation. It’s also the click of genetic switches. Epigenetics has ushered Lamarck back to the platform. He wasn’t invited by Godfrey-Smith, but he deserves to be heard, not in spite of the fact that he makes things messy, but because of it. Epigenetic messiness conforms much more tidily to the contours of the real biological world than do the equations of Ronald Fisher and John Maynard Smith. There’s an even more important uninvited contributor to the debate: wondering, thrilling doubt. It should have been the keynote speaker.

But all this is churlish. Other Minds is a superb, coruscating book. It’s exciting to see bottom-up philosophy – philosophy that starts on the reef and in the sand and then crawls slowly up towards abstraction. That’s how all philosophy should be done. We’d know a lot more about consciousness and the mind–body problem if philosophers could shed their fastidious disdain for facts and get out more, particularly with a diving mask and fins.