The Fifth Miracle: The Search for the Origin of Life by Paul Davies Allen Lane, The Penguin Press 260pp £18.99 in UK
Does life hold any real meaning? Are we here for a reason or are we simply the product of fortuitous but wholly directionless chemical reactions which occurred billions of years ago and eventually led to life?
The answer to this question, grist for the philosopher's mill for generations, lies not on Earth but in the immensity of outer space, argues Professor Paul Davies. Find alternative life by identifying one truly unique Martian microbe, locating slime mould growing under the frozen oceans of a Jovian moon or by reconstituting freeze-dried bacteria hitchhiking on the back of a comet and you go a long way towards providing answers, he believes.
Davies dives headlong into these murky philosophical waters in his latest book, The Fifth Miracle, taking the reader along for the ride as he grapples with the very basis of human existence. Yet we are not flung on to a whiteknuckle, white-water ride but rather launched on a gentle, slowboat journey of discovery as he teases out the complex science that is life.
His title is taken from the Book of Genesis but the book's subtitle better explains his purpose - "The Search for the Origin of Life". Life for Davies, however, is not limited to what one might find knocking about the Earth. What if life actually originated on Mars and then made its way here? What if we live on one of many waystations dotted across the universe where life forms flourish? And, more fundamentally, he asks what if the convoluted laws that dictate the operation of the universe actually ensure that life occurs. Is this a bio-friendly universe where life is inevitable?
"If it transpires that life emerged more or less on cue as part of the deep lawfulness of the cosmos - if it is scripted into the great cosmic drama in a basic manner - it hints at a universe with a purpose. In short, the origin of life is the key to the meaning of life," he says.
Professor Davies is an engaging writer, gently coaxing understanding and comprehension in the reader no matter how complex the subject matter. This latest offering is no exception as he tours such exotic territory as the Second Law of Thermodynamics and entropy, self-replicating organic molecules, and the biochemistry of the genetic code.
Yet he skilfully avoids expecting too much from the non-scientific reader. There are no formulas, no mathematical jigs and reels, and although the science is real there is nothing of the "boring but worthy" about it.
He is fully in his stride, for example, when he examines evidence that Earth life might after all have originated on Mars, to be sent earthward after a collision with an asteroid or comet. This is not fanciful conjecture: there are logical and scientific reasons to believe this might have happened and to suppose that Mars might have been better favoured to serve as the cradle of Earth life. "It is hard to avoid the conclusion that if there was life on Mars between 3.5 and 4 billion years ago, then live Martians will inevitably have taken up residence on Earth."
He is also wholly convinced that there was life on Mars in the past and there may still be life deep beneath the Red Planet's desiccated surface today. His confidence is again based solidly in science and the chain of discoveries of Earth-bound microbes that can withstand extreme conditions. They have been discovered at depths, pressures and temperatures which only a few years ago would have been thought impossible to allow life. Yet there they are, thousands of feet under the seabed, or living in the boiling waters of underwater volcanic vents.
He is perhaps most powerful, however, when he allows philosophy to drift back into his arguments about life's origins and the possibility that the universe might in fact be structured in such a way that life wasn't chance, but inevitable. "For 300 years science has based itself on reductionism and materialism, leading inevitably to atheism and a belief in the meaninglessness of physical existence. A bio-friendly universe would mark a decisive shift."
Life is about chemicals and DNA and genetic codes, but it is also about information, he argues. A chemical formula such as DNA is information rich, not simply complex. "The secret of life lies not in its chemical basis, but in the logical and informational rules it exploits. Life succeeds precisely because it evades chemical imperatives."
He finds possible answers in a merger between poorly understood yet compelling laws of complexity theory and the Darwinian engine that powers evolution. "A blend of molecular Darwinism and laws of organisational complexity could offer a way forward. In such a scenario, relatively small replicator molecules form by chance and start to evolve by Darwinian means, but the process is sometimes aided, and even overridden, by organisational principles that confer specificity and information. These organisational principles served to amplify greatly the selectivity of the evolutionary process, and lead to sudden jumps in complexity rather than the incremental advance expected from Darwinian evolution acting alone."