The title of this book derives from Genesis, which describes how God made the world in a series of steps. The first four are named by Davies as the creation of the universe, the creation of light, the creation of the firmament, and the creation of dry land; the fifth step is the production of vegetation. This enumeration is, it seems, due to a misreading of Genesis, but Davies chooses to use it anyway in constructing his title. This theological introduction to the book might make you suppose that you are in for a concealed religious argument in favour of creationism, but the book is about science, not religion; only at the end does Davies allow a little metaphysics to creep in. He provides, in fact, a good popular up-to-date introduction to the question of how life originated. He is a physicist, not a biologist, but he is following in the footsteps of illustrious predecessors, notably Erwin Schrodinger, whose book What is Life? has had a profound effect on many thinkers. It may be that a knowledge of physics and cosmology provides a wide perspective on the subject that is sometimes lost in discussions of the detailed biochemistry.
Davies starts by considering what life is. This is a surprisingly difficult question to answer, as Schrodinger discovered. Davies concludes that life includes two basic characteristics, metabolism and reproduction. But there is no sharp division between life and non-life. In the past, some biologists and philosophers favoured vitalism—the notion that there is some indefinable essence in living things that distinguishes them from non-living—but this view is now thoroughly discredited within science. Organisms are physico-chemical systems and all their processes can be understood without invoking any metaphysical principles. In particular, they don't contravene the second law of thermodynamics, because they are open systems, not closed. They can reduce entropy (disorder) locally, but they inevitably increase disorder somewhere else to pay for it.
But Davies identifies a deeper puzzle. Living systems are highly organized, which means they embody information. But where does this information come from? There is no agreement about this, or even about whether there is a real problem here, but Davies is sure that there is. The information possessed by organisms must come from somewhere, he argues, but it cannot be local. "We must seek the origin of biological information in some sort of global context. That may turn out to be simply the environment in which biogenesis occurs. On the other hand, it may involve some non-local type of physical law, as yet unrecognized by science, that explicitly tangles the dynamics of information with the dynamics of matter." For Davies, the question of where the information content of organisms comes from is ultimately the same as the question of where the information content of the universe came from. We are coming perilously close to metaphysics again here.
Moving on from these very far-reaching considerations, Davies looks at more detailed questions about how self-reproducing structures might have arisen, including the origin of the genetic code. The central problem concerns the role of chance in this process: is the origin of life supremely improbable or is it something that is pretty much bound to happen, given the right circumstances? Experiments by Urey and Miller in the 1950s showed that amino acids could be easily produced by sending electric sparks through a mixture of methane, hydrogen, and ammonia, which was supposed to be similar to the atmosphere of the early earth. At the time this was thought to be an important advance in understanding how life began, but for various reasons that now seems unlikely to be so. The odds against life arising appear to be colossal, so the challenge is to find ways in which these odds could be shortened.
One proposal is to look to space for the origin of life. Panspermia, the notion that life has been brought to earth in comets or meteors, is an old idea that has recently been favoured by some scientists, including Francis Crick and Fred Hoyle among others, but it doesn't explain how life arose in the first place. But introduction of the material needed for life, as opposed to actual living organisms, is a different matter. Comets are rich in organic substances and during the formation of the earth it was repeatedly struck by comets and other bodies. These could have introduced organic material that might have been the seed of life. Of course, cometary impact might also have been destructive of newly commenced life, and it is therefore possible that life originated more than once, being introduced and destroyed on a number of separate occasions.
Until recently, life was generally supposed to have arisen in a warm pool at the margin of the ocean, but new discoveries have suggested other scenarios. Living organisms have been found in the most unlikely situations: in hot vents called black smokers in the ocean floor, where there is no sunlight and temperatures are up to 110 degrees centigrade, and in rocks at depths of half a kilometre or more. Some microbes may be able to live at temperatures as high as 170 degrees centigrade. It is unclear how bacteria got into these deep areas, but Davies inclines to the view that life was not originally a surface phenomenon at all but arose at depth within the earth, where it would have been relatively protected against impacts from space.
If this idea is right, it sheds new light on the controversy about life on Mars, Life on the Martian surface may well be impossible, but conditions deep within the Martian rocks might not be all that different from what they are on Earth. Planetary cross-contamination, due to impact from meteors, may have happened more than once in the history of Earth and Mars, and other bodies in the solar system could be involved as well. It is unlikely that organisms could survive in interstellar space, even inside rocks, but they might do better inside comets, in which case microbial life, at least, may be widespread throughout the galaxy and even the universe. Davies rightly insists that the discovery of past or present life on Mars would be of the greatest philosophical importance.
Finally Davies touches on the most fascinating but also most difficult question of all. Even if life does occur more or less inevitably given the right circumstances, does it also inevitably evolve to become more and more complex and, ultimately, achieve intelligence? Is mind written into the structure of the universe? Stephen Jay Gould has famously opposed this view, but Davies believes that "the essential architecture of multicellular organisms might well be the product of certain mathematical principles of organization". He admits that here he is following his heart rather than his head. On the one hand we have "the nihilistic philosophy of the pointless universe", while on the other we have "an alternative view, admittedly romantic, but perhaps true nevertheless … a universe in which the emergence of thinking beings is a fundamental and integral part of the overall scheme of things. A universe in which we are not alone." Personally, I'm not sure that I can follow him in this optimism, but the merit of his book is that he presents the evidence fairly and you can make up your own mind.