This metaphoric, metabolic, river of life flows forward and is continually splitting up into separate streams, those of the newly evolving species, as it advances; likewise we see countless such specific streams in the past becoming less and less, mere trickles, and eventually drying up as this or that rarity becomes extinct. In spite of these losses the advancing stream has extraordinary powers of building itself up. Life, if unchecked and with sufficient food to nourish it, would in all too short a time smother the world. We see it pushing itself into all kinds of unlikely corners and parasitically into the bodies of other forms of life. Far back in the fossil record of the Paleozoic age, we see branches of the stream leaving its original home in the sea and advancing upon the newly raised continents of the land, first the plants derived from the marine algae and then the animals feeding upon the plants.
When we look at the life that has invaded the land and consider it as a floral and faunistic layer, the biosphere as it is sometimes called, covering the earth, we realise how thin a film it is compared with the bulk of the globe; it is like a mould growing on the surface of a cheese, or like the bloom on the surface of a plum. We ourselves are part of that film; how insignificant it might seem to a distant observer from another world...
...is it entirely folly to compare this living stream with a physical river system? We see that as it flows in time it is indeed like a river flowing in space,
but in reverse.
A physical stream always runs downhill, rarely divides into branches, but is fed by little tributaries - just the opposite of our stream of life.
The fact is so obvious...
Like the rest of the universe, a physical stream of water is obeying the second law of thermodynamics; manifesting the property we term entropy.
Erwin Schroedinger, in his remarkable little book "What is Life" and also in his "Science and Human Temperament" suggested that one of the characteristics distinguishing a living organism from the rest of the material world is the fact that it feeds upon "negative entropy". He explains what he means as follows:
It is by avoiding the rapid decay into the inert state of "equilibrium", that an organism appears so enigmatic; so much so, that from the earliest times of human thought some special non-physical or supernatural force (vis viva, entelechy) was claimed to be operative in the organism, and in some quarters is still claimed.
How does the living organism avoid decay? The obvious answer is: by eating, drinking, breathing and (in the case of plants) assimilating. The technical term is metabolism. The Greek word means change or exchange.
Exchange of what?
Originally the underlying idea is, no doubt, exchange of material. That the exchange of material should be the essential thing is absurd. Any atom of nitrogen, oxygen, sulphur, etc., is as good as any other of its kind; what could be gained by exchanging them?
What then is that precious something contained in our food which keeps us from death? That is easily answered. Every process, event, happening - call it what you will; in a word, everything that is going on in Nature means in increase of the entropy of the part of the world where it is going on. Thus a living organism continually increases its entropy - or as you might say, produces positive entropy - and thus tends to approach the dangerous stat of maximum entropy, which is death. It can only keep aloof from it, i.e. alive, by continually drawing from its environment negative entropy - which is something very positive as we shall immediately see. What an organism feeds on is negative entropy. Or, to put it less paradoxically, the essential thing in metabolism is that the organism succeeds in freeing itself from all the entropy it cannot help producing while alive.
... it is clear that throughout the whole organic progression from the simpler molecules up to the more advanced animal structures we see higher and higher levels of integration being developed... It is the simpler side of it, that of the living stream "marching up hill" that I find interesting in relation to the analogy of a river in reverse. This idea may be thought just too naive to be considered, but sometimes the simple hides the more profound.
Of course I realise that any animal goes up hill by using fuel just as does a man-made engine - and as a rule it may be driven up mountains, or from the sea on to the land (or in the reverse direction) by competition for food; and further that it is the great reproductive pressure, driving its stream forward, together with new adaptations fitting the animal to more and more difficult terrains, that we are considering, and not simply upward locomotion. Nevertheless out of this process of evolution, from somewhere has come the urge, or love of adventure, in Man, that can drive him to risk his life in climbing Everest or in reaching the South Pole or the Moon. Is it too naive to believe that this exploratory drive, this curiosity, has had its beginnings in something that is fundamental to the stream of life? ...
I think it likely that the "forces" of curiosity, love and the numinous also belong to the part of the Universe that is consciousness but that they are somehow experienced not by means of the ordinary bodily sense organs...