And, of course, you are something more than a mere organism. You could not be reading these words unless you were the fortunate possessor of a mind — perceiving and pondering, planning and remembering, imagining, communicating, acting. If your mind failed you — as it can in depression or psychosis or dementia — your life might fail you also. “For seeing we are not maisters of our owne affections, we are like battered Cities without walles, or shippes tossed in the sea, exposed to all matter of assaults and daungers, even to the overthrow of our own bodies”, wrote the 16th-century physician, Edward Jorden. Our lives are guided by the light of our agile minds.

Each of us, then, is a physical system, a living creature, a conscious mind, three in one and one in three — and Hippocrates was right: “to know the nature of man, we must know the nature of all things”. But how are these three great ingredients of ours interrelated?

In the 19th century many thinkers, like Pasteur, the French microbiologist, regarded the emergence of life from matter as an unfathomable mystery, the expression of an élan vital. Nowadays just about everyone accepts that rather than being an irreducible mystery, life is simply the set of processes that allows organisms to use energy from their surroundings to reproduce themselves. Rather than being one unfathomable thing, it is the coherent operation of a great many intricate but thoroughly fathomable things.

Although we mostly accept that life emerged from matter by natural processes, many of us are more reluctant to accept that mind also emerged from living things by natural means. Here the notion of élan vital lives on: we hunt for a magic formula that will conjure “the wine of experience from the water of the brain” — and are somehow perversely consoled by the sense that it won’t be found.