Mendel's Demon: Gene Justice and the Complexity of Life [Paperback]

In this superbly written account, Ridley clearly explains the advantage sex has in the evolution of life. He uses the children's game of Chinese Whispers [called Gossip in my childhood] to explain how evolution operates. In Gossip [forgive the chauvinism], a group of children whisper a message from one to another. Record the original message "when the tiger comes, freeze." Compare it with the version expressed by the final child. There will certainly be changes. In almost all occurrences, the errors are in misunderstood whole words, not just letters - "freeze" becomes "wheeze." The "words" of life are our genes. Acting as instructions to forming a new individual, the message must be clear enough to build the organism. That organism must survive to produce another. Sex provides ways of assessing the message to assure its validity before generating an offspring.

Ridley goes on to discuss how complex life forms emerged. The most important steps were the protecting of DNA in a cell nucleus and the addition of mitochondria. Mitochondria are the energy modules of cells - chloroplasts in plants probably being the best known. Their joining the nuclear cell provided a trade-off. Mitochondria were given a place to live, paying rent by transferring much of their DNA to the cell's nuclear version. Once these two changes had been achieved, sex evolved with mechanisms to overcome the problems of DNA playing Gossip. Ridley shows how the processes surrounding sex overcome the mistakes that inevitably occur in the copying process. Gross errors don't survive - indeed they rarely achieve the development level of a fetus. The apparent dichotomy here is that while reducing errors may mean conserving an organism's traits, it may also reduce the diversity necessary to survive in a changing environment. The balance is delicate, as the fact that 99.9 per cent of all species having gone extinct over time testifies.

Ridley sensibly brings each detailed description of the cell's processes back to how it relates to humans. This ploy is highly successful in making the book readable and focussed. It also builds a framework for the concluding chapters. After his thorough analysis of the procedures of reproduction and evolution, Ridley goes on to some highly speculative notions about the future. He notes that our species carries more genetic errors across generations than any other species. Could this error rate lead to what he calls "mutational meltdown"? Possibly, but not likely. Having speculated on conditions of life on alien worlds, he uses those ideas to suggest future scenarios to prevent that "meltdown." That bugaboo of today's society, cloning, Ridley dismisses as too vulnerable to natural selection. Instead, he sees gradually improving methods in using genes for therapy, organ replacement or repair, possibly even a drastic change in gender identity.

Ridley's almost anecdotal style makes this overview of a complex topic an absorbing read. Reaching from deep history to a plausible future he covers much ground. His imagery retains your attention and he carefully builds your knowledge as you follow his lead. He's also careful with his science. No assertions are put forward without good foundation, and where the evidence is lacking or slim, he cautions us about coming to conclusions. The balance is so carefully maintained that this book might be considered a call for research in particular areas. Formidable and challenging, this is a delightful book for countless reasons. Intriguing questions, bold but realistic speculation, sound science vividly presented. A rich treasure, this book will be valuable until all Ridley's questions are resolved. [stephen a. haines - Ottawa, Canada]