The first chapter is about the notoriously difficult problem of the origin of life. Lane finds that the most likely setting for this is the deep-sea hydrothermal vents. We usually think of these in terms of "black smokers", which in spite of their high temperature are home to an astonishing variety of life. These vents are volcanic, but there is also a second type of vent which is less well-known and is not volcanic, therefore cooler. These are called alkaline vents (black smokers are acidic).
Lane favours alkaline vents as the likely sites for the origin of life, both because of their chemistry and because their microscopic structure, with numerous interconnecting compartments, provides "an ideal hatchery for the origin of life". They are also long-lived—40,000 years or more—and were more plentiful on the early earth.
The second chapter takes these ideas further as Lane considers the origin of DNA from RNA, its likely precursor. This, it seems, could have happened surprisingly easily in the alkaline vents. But much uncertainty remains. "There is much in this tale left unsaid, many puzzles skipped over in an attempt to reconstruct a story that makes some kind of sense, at least to me."
The next topic is photosynthesis. This evolved in bacteria, in two stages, and was the main source of oxygen in the early atmosphere, as it still is today. The process both provides energy by splitting water into hydrogen and oxygen and allows the synthesis of organic compounds. As an aside, Lane notes that if current attempts to find a way of doing this in the laboratory succeed we will have access to a boundless supply of non-polluting energy and no increase in atmospheric carbon dioxide.
For most of the time that life has existed on this planet it was microbial. Nothing more complicated evolved until the arrival of the complex (eukaryotic) cell. Crucial to this was the incorporation in the cell of bacteria, which became our mitochondria (energy-producing organelles). There seems to have been nothing inevitable about this; the world might quite well still be home only to prokaryotes (bacteria).
So much for the inevitability of complex life on earth or of human consciousness. The world is split in two. There are the eternal prokaryotes and the kaleiodoscopic eukaryotes. The transition from one to the other seems not to have been a gradual evolution, no slow climb to complexity as limitless populations of bacteria explored every conceivable variation. Certainly vast populations of bacteria explored all feasible avenues, but they remained forever bacteria, stymied by their inability to expand in size and energy at the same time. Only a rare and fortuitous event, a collaboration between two prokaryotes, one somehow getting inside the other, broke the deadlock. An accident.
Once complex cells appeared they rapidly acquired sex. The well-known puzzle about this is that it ought to be disadvantageous, since asexual reproduction by cloning should quickly outstrip it. So why does it exist? A popular theory is that it provides genetic variety that is needed to resist parasites, but Lane thinks this is only part of the story. Whether sex will be beneficial or not depends on a variety of factors, which is why some organisms vary their reproductive strategy between cloning and sex. But very few are wholly asexual.
Animals differ from plants in being able to move about. In many cases this is enabled by muscles and Lane has a chapter on the evolution of muscle contraction. This depends on structural and chemical mechanisms that Lane describes in some detail and which have their roots far back in evolution. "The ancestor of all living eukaryotes was motile."
Sight, as opposed to the mere ability to detect light, appeared fairly suddenly in the fossil record, about 540 million years ago. More than one type of eye has evolved. The human eye is often said to have design flaws when compared to the eyes of octopus and squid: in our case the light has to pass through a layer of nerve fibres before reaching the light-sensitive cells of the retina, and there is a blind spot where the optic nerve exits the eye. But Lane thinks there may be advantages to our arrangement that are not obvious and we should be cautions in making assumptions. He quotes Leslie Orgel's dictum: "Evolution is cleverer than you are."
Later developments in evolution discussed by Lane include warm-bloodedness, a characteristic of mammals and birds and possibly of the dinosaurs, and consciousness, which he thinks is probably present to some extent in all animals with brains.
The final chapter, 'Death', considers the possibility of extending human life, and especially healthy human life. Lane is optimistic about this. Sometimes an apparently trivial genetic variation can have astonishing effects. Researchers in Japan found that people with a change in a single letter of their mitochondrial DNA had only half the normal chance of developing any age-related illness and were twice as likely to live to 100. He says he knows of no other fact as shocking as this in all medicine.
Some readers may be put off by the amount of biochemistry that is discussed in the book, even though there are no chemical equations or structural formulas. But Lane is a stimulating writer who is adept at dealing with complicated and contentious ideas in a way that makes sense to non-specialists,
24-05-2016