Strands of Life

Ronald Bailey from the August/September 2000 issue

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"What is truly strange," writes Ridley, "was that each of the eight genes affected a different part of the fly and they were lined up in the same order as the part of the fly they affected. The first gene affected the mouth, the second the face, the third the top of the head, the fourth the neck, the fifth the thorax, the sixth the front half of the abdomen, the seventh the rear half of the abdomen, and the eighth various other parts of the abdomen." To appreciate how odd this was, explains Ridley, one must appreciate how random the locations of genes usually are: "[T]here is very little rhyme or reason for where a gene lies. Sometimes it needs to be close to certain other genes. But it is surely rather literal of Mother Nature to lay these homeotic genes out in the order of their use."

As important, it turns out that each of the genes contains the same bit of a "text" that is always 180 "letters" long. Now known as the "homeobox," this information "is the bit by which the protein made by the gene attaches to a strand of DNA to switch on or off another gene. All homeotic genes are genes for switching other genes on or off," explains Ridley. Such genes essentially tell other genes to get to work on making heads, abdomens, and tails. If the head homeotic gene fails to switch on the cascade of genes that construct the head, then the animal won't develop a head.

Having identified the homeobox segment, researchers searched for it in other organisms. Mice, it turns out, have 4 clusters of Hox genes, which are laid out in the same head-to-tail way as they are in the fruit fly. Humans have the same Hox clusters as mice, one of which is located on chromosome 12. Interestingly, the first gene in line is the first one to be expressed followed in temporal order by the others. "All animals develop from the bow to stern ...At the level of embryology we are glorified flies," jokes Ridley. "The evolutionary implication is that we are descended from a common ancestor with flies which used the same way of defining the pattern of the embryo more than 530 million years ago, and that the mechanism is so good that all this dead creature's descendants have hung onto it."

Ridley explores how genomic research will eventually help doctors treat heart disease, cancer, dementia, arthritis, diabetes, and other diseases. For example, a defect in the ADA gene on chromosome 20 causes severe combined immune deficiency (SCID), which renders the sufferer incapable of fighting off infections. Originally, researchers thought that SCID could be cured if the normal gene could somehow be inserted into a patient's genome. In a pioneering experiment in 1990, French Anderson and Michael Blaese used genetically engineered retroviruses to deliver normal ADA genes to a 3-year-old girl. Her immune response improved somewhat, though not completely. In late April, French scientists reported that two infants suffering from another type of SCID were developing normal immune systems after normal genes were introduced into their bone marrow using genetically modified viruses. Gene therapy may have its first unqualified success.

Ridley is not only good at explaining the science, but is also sound on policy. Unlike so many other authors of books on genetic science, he doesn't waste a lot of time decrying the supposed ethical conundrums posed by scientific progress. He crisply dismisses ethical concerns about the type of gene therapy that cures diseases like SCID. "It is just another form of therapy and nobody who has watched a friend or relative go through chemotherapy or radiotherapy for cancer would begrudge them, on far-fetched safety grounds, the comparatively painless possibility of gene therapy instead," he asserts.

Ridley also investigates the long, sorry history of eugenics. He documents not only well-known Nazi attitudes on the subject but also those of the Fabian socialists, including H.G. Wells, John Maynard Keynes, and George Bernard Shaw. They all believed, notes Ridley, in "the urgent need to stop stupid or disabled people from breeding." H.G. Wells was particularly creepy, writing, "It has become apparent that whole masses of human population are, as a whole, inferior in their claim upon the future. To give them equality is to sink to their level, to protect and cherish them is to be swamped by their fecundity." Wells did have a touch of compassion in him, however. "All such killing," he insisted, "will be done with an opiate." Ridley concludes his discussion of eugenics by insisting on a distinction ignored by many who indiscriminately inveigh against all forms of genetic manipulation. "Many modern accounts of the history of eugenics present it as an example of the dangers of letting science, genetics especially, out of control," he writes. "It is much more an example of the danger of letting government out of control."

Such clear thinking is particularly valuable on a topic that often gives rise to muddy arguments. Indeed, Genome disappoints on only one count: It was written at the dawn of an enormously important era. As exciting as the news about genetic research has already been and will certainly be later this year, it will be even more breathtaking over the next few decades. According to Steve Fodor, president of the biotechnology company Affymetrix, "Ninety-nine percent of people don't have an inkling about how fast this revolution is coming." To Matt Ridley's credit, readers of Genome will have far more than an inkling.